C++ Language

First Post:

2020-02-24

Last Update:

2023-03-15

Word Count:

16.6k

Read Time:

86 min

C++ language

Learn：

https://www.programiz.com/cpp-programming/variables-literals

Keywords of C++

alignas(c++11)	 //声明结构体或类的对齐数
alignof(c++11)	 //查看结构体或类的对齐数
and				 //等价于 &&
and_eq			 //等价于 &&=
asm				 //汇编语句
auto			 //自动类型
bitand			 //等价于  &
bitor			 //等价于　|
bool			 //bool类型
break			 //跳出当前循环,或switch
case			 //结合switch使用
catch			 //捕获异常
char			 //1字节变量
short			 //2字节变量
signed			 //声明为有符号类型
unsigned		 //声明为无符号类型
char16_t(c++11)  //常使用于Unicode字符
char32_t(c++11)	 //常使用于Unicode字符
int				 //默认４字节
long			 //不比int类型小的类型
class			 //类,或者声明模板类型
compl			 //等价于 ~
concept(概念Ts)	 //专家级别使用
const			 //声明常变量
constexpr(c++11) //用作函数时,是在编译是进行函数调用的,类似与宏
const_cast		 //常变量强制转化为其他变量类型
continue		 //结合循环来使用	
decltype(c++11)  //与auto差不多,可以用于某个不确定多个参数类型的模板函数
default			 //结合switch来使用
delete			 //释放new出来的东西
new				 //开辟内存
do				 //配合 while构成循环
explicit		 //不能隐式构造
export			 //专家级别使用...
extern			 //改变某个变量的作用域,常用在不同文件中使用同一个变量
float			 //4字节的浮点类型
double			 //８字节的浮点类型
for				 //for循环
goto			 //跳转
if				 //判断
friend			 //给类中的一些函数使用,可以访问类中的私有成员变量
inline			 //内联声明, 编译器对该函数进行优化,类中函数和模板函数默认代这个参数
mutable			 //在lambda表达式中使用表示为传递进来的变量可以被赋值
namespace		 //声明命名空间　
noexcept(c++11)  //声明为不抛出异常,利于编译器的优化 
not				 //等价与 !
not_eq			 //等价于 !=
nullptr(c++11)	 //c++11以后声明空指针类型,主要解决模板函数中的参数问题
operator		 //操作运算重载
or				 //等价与 |
or_eq			 //等价于 |=
private			 //声明成员为私有的
public			 //声明成员为公共的
protected		 //声明成员为保护的
register		 //声明在寄存器里的变量
reinterpret_cast //常用在　一个类型的指针转化为另一个类型的指针
requires(概念TS) //一个概念,目前还没有编译器实现
return	 //函数的返回
static	 //声明变量为静态的
sizeof	 //获取某个变量的大小
static_assert(c++11) //静态断言, 常用
static_cast //静态转化
struct	 //结构体类型
switch	 //switch分支判断结构
template //声明模板
this	 //this指针, 常用在class和struct
thread_local(c++11)  //结合线程来使用
throw	 //抛出异常
true	 //bool类型的真
false	 //bool类型的假
try		 //异常尝试
typedef	 //改变变量名称
typeid	 //获取类型的id号
typename //声明模板类型
union	//联合体
using  //可以替换typedef的功能
virtual //虚函数
void   //空类型
volatile //直接声明为定死的常量
wchar_t //表示宽字符的
while   //循环
xor		//异或 ^
xor_eq  //　^=

实例

#include <iostream>
#include <typeinfo>
#include <cassert>
#include <map>
//#include <algorithm>
//#include <vector>
//#include <list>
//#include <stack>
//#include <future>
//#include <functional>
using namespace std;
//---------------------------------------------------------------
//alignas
struct alignas(8) S {};
struct alignas(1) U {S s; }; //bad
struct Foo {
	int i;
	float f;
	char c;
};
struct Empty {};
struct alignas(64) Empty64 {};
struct alignas(1) Double { double d; };
struct Obj {char a; int b;};
//sizeof(Obj) == 8
//alignof(Obj) == 4
void alignInfo() {
	cout << "Alignment of" << endl
		<<"_char			 : " << alignof(char) << endl
		<<"_pointer          : " << alignof(int*) << endl
		<<"_class Foo        : " << alignof(Foo) << endl;
}
//---------------------------------------------------------------
//and
void showAnd() {
	int a = 3;
	int b = 4;
	if(a == 3 && b == 4) {
		cout << "&& a = 3, b = 4";
	}
	if(a == 3 and b == 4) {
		cout << "and a = 3, b = 4";
	}
}
//---------------------------------------------------------------
//and_eq   <=>  &=
void testAnd_eq() {
	bool a = false;
	bool b = true;
	b = b and_eq a;
	cout << b << endl;
	bool c = true;
	c and_eq a;
	cout << "c: " << c << endl;
}
//---------------------------------------------------------------
//not <=> !
void testNot() {

	bool a = true;	
	bool b = not(a);
	cout << b;
}
//---------------------------------------------------------------
//not_eq <=> !=
void testNot_eq() {
	bool a = true;
	a not_eq(a);
	cout << a;
}
//---------------------------------------------------------------
//or <=> |
void testOr() {
	int a = 3;
	cout << a or 2;
}
//---------------------------------------------------------------
//or <=> |=
void testOr_eq() {
	int a = 3;
	a or_eq 4;
	cout << a;
}
//---------------------------------------------------------------
void showAsm() {
	asm (
	"movq $60, %rax\n\t" //the exit syscall number on linux
	"movq $2,  %rdi\n\t" //this program returns 2
	"syscall"
	);
}
//---------------------------------------------------------------
int get_fun(int x) {
	return x + 1;
}
double add(double a, double b) {
	return a + b;
}
void showAuto() {
	auto a = 1 + 2;
	cout << "type of a: " << typeid(a).name() << endl;
	auto b = add(1, 1.2);
	cout << "type of b: " << typeid(b).name() << endl;
	auto c = {1, 2}; //初始化列表
	cout << "type of c: " << typeid(c).name() << endl;

	auto my_lambda = [](int x) { return x + 3; };
	cout << "type of my_lambda: " << typeid(my_lambda).name() << endl;

	auto my_fun = get_fun;
	cout << "my_fun: " << my_fun(3) << endl;

	cout << "type of my_fun: " << typeid(my_fun).name() << endl;

}
//---------------------------------------------------------------
void showBitAndOr() {
	auto a = 3l; //long int
	auto b = 4;
	auto c = a bitand b;
	auto d = a bitor b;
	cout << "c: " << c << "d: " << d;
}
//---------------------------------------------------------------
void testBool() {
	bool a = true;
	bool b = false;
	*(reinterpret_cast<char *>(&a)) = -1;
	cout << a << " " << b << endl;
	if(a == true) {
		cout << "i'm true";
	}else if(a == false){
		cout << "i'm false";
	}else {
		cout << "What?";
	}
}
//---------------------------------------------------------------
void testBreak() {
	int a = 10;
	for(;;) {
		for(;;) {
			++a;	
			if(a > 1000) break;
		}	
		if(a > 100000000) break;
	}
}
//---------------------------------------------------------------
void testCompl() {
	int a = -3;
	int b = compl(a); // compl(a) <=> ~a
	cout << b;
}
//---------------------------------------------------------------
int fact(int n) {
	return n < 1 ? 1 : (n * fact(n - 1));
}
constexpr int factorial(int n) {
	return n < 1 ? 1 : (n * factorial(n - 1));
}
template<int N>
struct NN{
	void print() { cout << N << endl;}
};
void testConstExpr() {
	auto a = fact(4); //运行时计算
	auto b = factorial(4); //编译时计算, 类似于宏定义计算
	cout << "a: " << a << " b: " << b << endl;
	char group[factorial(5)];
	NN<factorial(8)> nn;
	nn.print();
}
//---------------------------------------------------------------
/*
void testThread(const int &a) {
	cout << "thread"	
}*/
void testConst_cast() {
	const int i = 3;
	//const int*
	int *p = const_cast<int*>(&i);
//	std::thread aa([&i](){ testThread(i); });
	*p = 5;
	cout << p << endl << &i << endl;
	cout << i << "  " << *p << endl;
}
//---------------------------------------------------------------
//decltype 与 auto 十分相近
struct A {A(int n) : x(n) {} double x;};
void testDecltype() {
	const A* a = new A(0);
	auto aa = a->x;
	decltype(a->x) y; // 相当于auto  aa = a->x
	decltype((a->x)) z = y; //相当于 auto & z = y, 引用
	y = 3;
//	z = 4;
	cout << y << endl << z;
}
// 写一个相加函数, 实现不确定类型相加的函数
template<typename T, typename U>
auto add(T a, U b) -> decltype(a + b) { //decltype(a + b) 推导出返回值类型
	return a + b;
}
/*
//陷阱: auto 
template<typename T, typename U>
auto add(Ta, Ub) {}
	return a + b;
	// return a + b 与 return (a + b) 可能表示的意义不同, 后者可能代表引用
}*/
//---------------------------------------------------------------
struct Base { virtual ~Base() {} };
struct Drive : Base {
	virtual void name() {}
};
void testDynamic_cast() {
	Base *b1 = new Base;
	//这里会调用不成功
	if(Drive *d = dynamic_cast<Drive *>(b1)) {
		std::cout << "downcast from b1 to d successful" << std::endl;	
		d->name(); //safe to call
	}
	
	Base *b2 = new Drive;
	//这里会调用成功
	if(Drive *d = dynamic_cast<Drive *>(b2)) {
		std::cout << "downcast from b2 to d successful" << std::endl;	
		d->name(); //safe to call
	}
	//对于dynamic_cast转换引用,若转化失败,则会抛出异常
	//dynamic_cast 在运行期进行检查 
	/*
	Base bb; 
	Drive& cc = dynamic_cast<Drive&>(bb);
	*/
}
//---------------------------------------------------------------
enum Color { red, green, blue };
//老的版本中,若出现 enmu Color2 {red, green, blue}; 就会出先重复的元素,就会报错
void testOldEnum() {
	Color r = red;
	switch(r) {
		case red:
			std::cout << "red" << std::endl;
		break;
		case green:
			std::cout << "green" << std::endl;
		break;
		case blue:
			std::cout << "blue" << std::endl;
		break;
		default:
			std::cout << "what ?" << std::endl;
	}
}
enum class NewColor {red, green, blue = green + 12};
enum class MyColor : short {black}; //通过short指定元素的类型为short

//若以bool作为函数参数, 建议使用enum来代替bool参数.
enum class IsGood {Yes, No};
enum class IsOk {Yes, No};
void enumBoolTest(IsGood isGood, IsOk isOk) {
}

void testNewEnum() {
	NewColor r = NewColor::blue;
	switch(r) {
		case NewColor::blue: {
			cout << "new blue" << endl;						 
		} break;
		case NewColor::red: {
			cout << "new red" << endl;						 
		} break;
		case NewColor::green: {
			cout << "new green" << endl; 
		} break;
		default:
			cout << "new what?" << endl;
	}

	int i = static_cast<int>(blue) + static_cast<int>(NewColor::blue);
	cout << "blud + NewColor::blue = " << i << endl;
	enumBoolTest(IsGood::Yes, IsOk::No);
}
//---------------------------------------------------------------
//test explicit
struct AA {
	AA(int) {}
	AA(int, int) {}
	operator int() const { return 0; } //AA可以默认的转化为int类型
};
struct BB {
	explicit BB(int) {}
	BB(int, int) {}
	explicit operator int() const { return 0; }
};
void testExplicit() {
	AA a1 = 1; //等价于 AA a1 = AA(1);
	//而BB就不能 BB b = 1;
	AA a2 = {3, 5}; //等价于 AA a1 = AA(3, 5);
	BB b2 = {3, 5}; //BB中B(int, int)没有加explicit
	int i = a1; //能通过
	//而BB就不能 int i = b2;
	//将BB强转.
	int na2 = static_cast<int>(a1);
	int nb2 = static_cast<int>(b2); //强转explicit　可以
	AA a4 = (AA)3;
	BB b3 = (BB)4; //通过C语言方式强制转换, 可以
}
//---------------------------------------------------------------
//friend
class MyClass {};
class Friend {
	private:
		int data; //private member
	friend std::ostream &operator << (std::ostream &out, const Friend &o);
	//Mycla　类是Fried类的好友, 只是单向
	template <typename T> friend class MyCla;  //every MyClass<T> is a friend of Friend
	template <typename T> friend void f(T) {} //every f<T> if a friend of Firend
	public:
	Friend(int x) : data(x) {}
	operator int() const { return this->data; }
};
//这样可以拿这个函数当公共函数访问私有成员
std::ostream &operator << (std::ostream &out, const Friend &f) {
	return out << f.data;
}
//若发生继承关系, MyCla不是, Friend2 的好友.
class Friend2 : public Friend { };

void testFriend() {
		Friend a = 44;
	cout << a;
}
//---------------------------------------------------------------
//goto
void testGoto() {
	auto i = 0;
NO:
	if(i < 5) {
		cout << i;
		i ++;
		goto NO;	
	}
}
//---------------------------------------------------------------
//inline
//尽量的减少栈空间开辟和回收操作
//类和模板函数,默认会加上inline进行优化.
//但不一定快
//inline 也可以与 namespace一起用， inline namespace
inline int plus(int a, int b) {
	return a + b;
}
class Inline {
	//在类中的函数里,编译器会默认加上inline进行优化
	public:
		void Member() const { std::cout << "hello\n"; }
		int vlaue() const { return this->m_value; }
	private:
		int m_value;
};
//---------------------------------------------------------------
//namespace
namespace XGroup {
	class A_ {
		int value;	
	};
}
namespace YGroup {
	class A_ {
		int value;	
	};
	class B_ {
		int value;	
	};
}
void testNmaespace() {
	XGroup::A_ a;	
	YGroup::A_ b;	
}
void testNamespace2() {
	using namespace XGroup;
	A_ a;
	using namespace YGroup;
	B_ b; //可以不用写 YGroup::B_
}
void testNamespace3() {
	namespace CGroup = XGroup;	
	CGroup::A_ a;
	using YGroup::B_;
	B_ b;
}
//没有名字的namespace
namespace {
	std::string astring("long"); //相当于　static std::string astirng
}
void testNamespace4() {
	cout << astring; //打印astring
}
//---------------------------------------------------------------
//noexcept
void noexCept() noexcept { //声明确定不会抛出异常,可以减轻编译器压力,利于优化代码.
	std::cout << "hello" << std::endl;
	//std::terminate(); abort(); exit(0);
}
void noexCept2() noexcept(false) { //等价于没写
	std::cout << "hello" << std::endl;
}
//---------------------------------------------------------------
void nullPointer(int *a) {
}
template<typename T, typename U>
void func(T t, U u) {
	t(u);
}
void testNullPointer() {
	//三者直接调用,结果一样
	nullPointer(0);
	nullPointer(NULL); //(void*)0
	nullPointer(nullptr); //std::nullptr_t 在c++11中有专有的类型
	//利用模板函数之后, NULL 模板函数推导为int
	func(nullPointer, nullptr);
	//不能调用　
//	func(nullPointer, NULL);
//	func(nullPointer, 0);
	//若想调用,需要强制转换　
	func(nullPointer, (int*)0);
	func(nullPointer, (int*)NULL);
}
//---------------------------------------------------------------
//operator
struct Operator {
	public:
		Operator(int x) : data(x) { }
//	operator int() const { return this->data; }
	int operator << (Operator const& o) const {
		return data + o.data;
	}
	int operator & () const { return data; }
	private:
	int data;
};
void testOperator() {
	Operator a = 10;
	Operator b = 5;
	Operator c = a << b; //实际实现相加
	cout << &c << endl; //采用去地址符号实现返回里面的值
}
//实例应用:
/*
struct AClass {
	~AClass() { delete m_value}
	AClass() : m_value(new int()) {}
	private:
	int *m_value;
}
void test() {
	Aclass A;
	Aclass B;
	A = B; //这种情况,里面的值m_value,会发生直接赋值,A和B直接指向同一块内存,
	//会发生两次析构,内存会错误.
	
} */
//使用操作符重载 = 来避免:
struct AClass {
	~AClass() { delete m_value;}
	AClass(const AClass& rhs) : m_value(new int(*(rhs.m_value))) {}
	AClass& operator = (const AClass& rhs) {
		*m_value = *(rhs.m_value);
		return *this;
	}
	private:
		int *m_value;
};
//---------------------------------------------------------------
//reinterpret_cast
void testReinterpret_cast() {
	//reinterpret_cast
	//static_cast
	//const_cast
	//dynamic_cast
	//c like cast　可以实现以上的大部分, 而dynamic_cast c语言这种方式不能实现的

	int a = 1;
	// 也相当于 char* p = (char*)&a;
	auto p = reinterpret_cast<char *>(&a); //转化为char*
	//不能char* b = static_cast<char*> &b;
	if(p[0] = 1) {
		std::cout << "the system is little endian\n";
	}else {
		std::cout << "the system is big endian\n";
	}
}
//---------------------------------------------------------------
//sizeof, before c++11
struct SizeofEmpty {};
struct SizeofBase { int a;};
struct SizeofDerived : Base{ int b;};
struct SizeofBit {unsigned bit : 1;};
void testSizeof() {
	SizeofEmpty e;
	SizeofDerived d;
	SizeofBase b;
	SizeofBit bit;
	cout << "sizeof empty: " << sizeof e << endl;
	cout << "sizeof derived: " << sizeof d << endl;
	cout << "sizeof base: " << sizeof(b) << endl;
	cout << "sizeof bit: " << sizeof(SizeofBit) << endl;
//	cout << "szieof void" << sizeof(void) << endl;
//	cout << "szieof int[]" << sizeof(int[]) << endl;
}
//---------------------------------------------------------------
//static
//最好要这么用
static int globalA = 0;
void printInfo() {
	static int localStatic = 0; //多线程不要这么用
	++ localStatic;
	cout << "globalA: " << globalA << " " << "localStatic: " << localStatic << endl;
}
struct Static {
	static int s; //注意: sizeof(Static) == 1, s的空间已经分配
};
int Static::s = 10;

struct HeHe {};
struct Static2 {
	static int a[];
	static HeHe foo;
	static Static2 ss;
};
//对成员进行实例化
int Static2::a[10];
HeHe Static2::foo;
Static2 Static2::ss;

//---------------------------------------------------------------
//static_assert c++11的一个宏, 在编译期进行检测
//assert 是在运行的时候进行检测
void testStaticAssert() {
	static_assert(sizeof(int) == 4, "only work for int of 32bit");
	static_assert(sizeof(long) == sizeof(long long),
			"only work for int of 32bit");
	int a = 5; //判断变量 a == b 采用assert
	int b = 5;
	assert(a != b && "error"); 
}
template<typename T>
void static_assertFun() {
	static_assert(alignof(T) ==4, "only for alignof 4");
}
//---------------------------------------------------------------
//typedef , 换名称
typedef unsigned long ulong;
class Comp {
	typedef std::map<int, ulong> Group;
	Group a; //相当于 std::map<int, ulong> a;
	void aa() {
		//std::map<int, ulong>::iterator iter = a.find(10)
		Group::iterator iter = a.find(10);
		//也可以使用: auto iter = a.fine(10);
	}
};
//---------------------------------------------------------------
//using 
//可以使用与namespace,也可以替换typedef
using newGroup = std::map<int, ulong>;

//using namespace std;

//---------------------------------------------------------------

int main(void) {
//	showAuto();
//	showBitAndOr();
//	showAsm();
//	testAnd_eq();
//	testNot();
//	testNot_eq();
//	testBool();
//	testBreak();
//	testCompl();
//	testConstExpr();
//	testConst_cast();
//	testDecltype();
//	testDynamic_cast();
//	testOldEnum();
//	testNewEnum();
//	testExplicit();
//	testFriend();
//	testGoto();
//	testNamespace4();
//	testOperator();
//	testReinterpret_cast();
//	testSizeof();
	testStaticAssert();

	return 0;
}

Class

C++析构函数中抛出异常问题

注意: 不要在析构函数中抛出异常

析构函数调用规则

先调用成员析构
再调用派生类析构

问题代码

分析代码如下

#include <iostream>
class A {
	public:
		A() {}
		~A() { std::cout << "A析构了.." << std::endl; }
};
//析构函数绝对不要抛出异常
class B : public A{
	public:
		B() {}
		~B() { std::cout << "B析构了.. " << std::endl; 
		throw std::string("B error"); } // 编译器默认析构函数: inline ~B() noexcept {}
	//编译器默认析构函数实现:
	/*
		inline ~B() noexcept {
			try {
			
			} catch(...) {
				std::terminate();	
				//析构函数绝对不要抛出异常
			}
		} 
	 */
	private:
		std::string m_value;
		/*
			在掉~B() 析构时候, 先调用 m_value的析构,再调用派生类 ~A();
		 */
};
void testClass_1() { //测试析构
	B *b = new B;
	delete b;
}
class EvilB : public B {
	public:
		~EvilB() noexcept(false) { throw std::string("error"); }
};
void testEvilB() {
	try {
		EvilB *b = new EvilB();	
		delete b;
		
	} catch(std::string e) {
		//没有捕获到异常,编译器已经调用std::terminate(),且程序崩溃
		//因为编译器为析构函数默认加入关键字 noexcept,可以加入关键字 noexcept(false) 
		//问题1 : 派生类虽然能够析构,若派生类析构函数也抛出异常,则程序就挂.
		//出现抛出两个异常, 则无法捕获.
		//问题2 : 若声明两次EvilB对象,析构两次时,则程序就会崩溃.
		std::cout << "catch your evil: " << e <<  std::endl;
	}
}
int main(void) {
	testEvilB();
	return 0;
}

正确做法

建议: 在类的构造函数中抛出异常

代码如下

#include <iostream>
#include <fstream>
#include <vector>
#include <cassert>

class A {
	public:
		A() {}
};
class B : public A {
	public:
		B() {}
		~B() { /*std::cout << "byebye B\n";*/ }
	private:
		std::string m_value;
};
class GoodB : public B {
	public:
		GoodB() : m_v(new char(10000000)) {}
		GoodB(const char* f) : m_file(f, std::ios_base::in) {
			//在构造器里进行抛出异常,而不是一直判断是否有错误来避免错误.
			if(!m_file.is_open()) throw std::string("Couldn't open file..\n");

			std::string line;	
			while(std::getline(m_file, line)) {
				m_info.push_back(line);
			}
		}
		void doIt( GoodB const&b) {
			if(b.isOpen()) {
				//do	
			}
		}
		//通过析构来提示.
		~GoodB() { assert((!isOpen()) && "open file: "); }
	private:
		char *m_v;
		std::fstream m_file; //外部文件 
		std::vector<std::string> m_info;
		//若作为状态判断,一般声明为私有函数, 通过assert来提示.
		bool isOpen() const { return !m_info.empty(); }
};
//循环构造, 内存崩溃
//想实现一个 std::out_of_memory 异常
void test() {
	int i = 0;
	for(;;) {
		try {
			++i;	
			if(i % 10000 == 0) std::cout << "count i: " << i << std::endl;
			GoodB b;	
		} catch(...) {
			return ;	
		}
	}
}
void test2(char *filename) {
	try {
//在构造时候进行抛出异常,重复抛出, 不会出现问题, 而在析构函数中抛出,程序则会崩溃
		GoodB b(filename);
		GoodB d(filename);
		b.doIt(b);
		//std::swap(b, d) //也不要抛出异常
	} catch(std::string msg) {
		std::cout << msg;
	}
}
int main(int argc, char** argv) {
	if(argc <= 1) return 1;
//	test();
	test2(argv[1]);
	std::cout << "exit!!!\n";
	return 0;
}

管理内存的几种方式

#include <iostream>
#include <memory>

static void versionOne();
static void versionTwo();

using namespace std;

int main(void) {

	versionOne();
	versionTwo();
	versionThree();
	return EXIT_SUCCESS;
}
void versionOne() {
	//c语言方式开辟内存
	int *ageC = (int*) malloc(sizeof(int));
	if(argC) {
		free(ageC);
	}
	char *c = (char*) malloc(100);
	free(c);

	//c++ 开辟内存方式
	int *age = new int(25);
	int *height = new int(160);
	//缺陷,容易忘掉free 或 delete
}

void versionTow() {
	//智能指针
	std::shared_ptr<int> age(new int(28));
	std::shared_ptr<int> height(new int(160));

	std::cout << "VersionTwo: you age is " << *age << ", and your height is "
		<< *height << std::endl;
	//不需要做任何事情, 内存会自动的释放掉
	//基本上,不会造成内存泄露问题
}

逐渐退化的虚函数

#include <map>
#include <iostream>
/*
	类虚函数遇到构造和析构就退化了
 */

class Event; //类的前置声明
class Event {};
class Base {
	public:
		virtual ~Base() {} //why? virtual
		Base(int _id) : m_id(_id) {}
		virtual void act(Event const&) = 0;
		virtual void print() const = 0;
		int id() const { return m_id; } 
	private:
		int m_id;
};
class Drived : public Base { //why public?
	public:
		void act (Event const&);
		void print() const;
		Drived(int id);
		~Drived();
	private:

};
class Grouped : public Base {
	public:
		void act(Event const&);
		void print() const;
		void addBase(Base* b);
		void removeBase(int id);
		Grouped(int id);
		~Grouped();
	private:
		std::map<int, Base *> m_info;
};
void test() {
	//int a = 1;
	/*
	Drived *info = new Drived(1);	
	Grouped *group = new Grouped();

	group->print();
	group->act(ev);
	group->addBase(info);
	group->removeBase(info->id());
	group->id();

	Base *baseGroup = group;
	baseGroup->act(ev);
	baseGroup->print();
	baseGroup->id();
	//removeBase()
	//addBase()
	//而基类的指针baseGroup中强制把派生类转换,而基类在虚函数中干的事,与派生类的一样
	//相当于派生类来实现函数,而不是基类.这就实现了指针对接口进行编程.
	delete group; //delete baseGroup;没有内存泄露,　与delete group等价
	delete info;
	*/
}

int main(void) {
	test();
	return 0 ;
}

虚函数几种实现方法

#include <fstream>
#include <iostream>
#include <string>
#include <vector>

struct Base {
	virtual void f() { std::cout << "base" << std::endl; }
	virtual void init() {}
	Base() {
		init();	
	}
};

struct Derived : Base { //结构体默认为public 继承, 类默认为 private
	void f() override { //加入override关键字,表示重写基类的f()虚函数
		std::cout << "derived overide" << std::endl;
	}
	void init() override { std::cout << "virtual init" << std::endl; }
} ;

struct Derived2 : Derived {
	public:
		void f() {}
		void init() {}
};

Base* factoryBase(int type) {
	Base* ret = nullptr;
	if(type == 0) {
		ret = new Base();	
	}else if(type == 1) {
		ret = new Derived();	
	}else if(type == 2) {
		ret = new Derived2();	
	}

	if(ret) ret->init();
	return ret;
}

void testVirtual() {
	//Base b;
	//Derived d;
	////虚函数调用通过引用
	////virtual funciton call through reference
	//Base& br = b;  //the type of br is Base&
	//Base& dr = d;  //the type of dr is Base& as well
	//br.f();
	//dr.f(); //在Derived类中已经对fun() 重写.
	//
	////虚函数调用通过指针
	////virtual function call through pointer
	//Base* bp = &b;
	//Base* dp = &d;
	//bp->f();
	//dp->f();

	////直接调用.
	////non-virtual function call
	//b.Base::f();
	//d.Derived::f(); //派生类
	//d.Base::f(); //基类
	////若在构造函数中或者析构函数中调用虚函数, 则会调用自身类中的虚函数,而不是派生类的重写的虚函数
	////虚函数特性还没体现
	Derived d;
}
int main(void) {
	testVirtual();
	return 0;
}

对象内存布局

普通对象

#include <iostream>
class A {
public:
	A() {
		std::cout << "A\n";
	}
	~A() {
		std::cout << "~A\n";
	}
private:
	int a = 1;
	int b = 2;
};

int main() {
	A a;
	return 0;
}

生成可执行文件ida反编译如下:

main

int __cdecl main(int argc, const char **argv, const char **envp)
{
  char v4[8]; // [rsp+0h] [rbp-20h] BYREF
  unsigned __int64 v5; // [rsp+8h] [rbp-18h]

  v5 = __readfsqword(0x28u);
  A::A((A *)v4);
  A::~A((A *)v4);
  return 0;
}

A::A()

void __fastcall A::A(A *this)
{
  *(_DWORD *)this = 1;
  *((_DWORD *)this + 1) = 2;
  std::operator<<<std::char_traits<char>>(&std::cout, &unk_2005);
}

A::~A()

void __fastcall A::~A(A *this)
{
  std::operator<<<std::char_traits<char>>(&std::cout, &unk_2008);
}

this指针即是堆栈上数据v4的地址。

在堆区上的普通对象

source

#include <iostream>
class A {
public:
	A() { std::cout << "A\n";}
	~A() { std::cout << "~A\n";}
	void test() { std::cout << "test\n";}
private:
	int a = 1;
	int b = 2;
};

int main() {
	A *a = new A();
	a->test();
	return 0;
}

生成可执行文件ida反编译如下:

int __cdecl main(int argc, const char **argv, const char **envp)
{
  A *v3; // rbx

  v3 = (A *)operator new(8uLL);
  A::A(v3);
  A::test(v3);
  return 0;
}

A::A()

void __fastcall A::A(A *this)
{
  *(_DWORD *)this = 1;
  *((_DWORD *)this + 1) = 2;
  std::operator<<<std::char_traits<char>>(&std::cout, &unk_2005);
}

与堆栈上的差不多，堆栈上的对象不用管内存泄漏问题，编译器调用析构函数，开辟在堆区的对象由于没有delete a，所有没有析构函数调用和内存的释放，出现内存泄漏。

拥有vital function

#include <iostream>
class A {
public:
	A() {
		std::cout << "A\n";
	}
	~A() {
		std::cout << "~A\n";
	}
	virtual void vir_1() {
		std::cout << "vir_1 A\n";
	}
	virtual void vir_2() = 0;

private:
	int a;
	int b;
};
class B : public A{
public:
	B() {std::cout << "B\n";}	
	~B() {std::cout << "~B\n";}	
	virtual void vir_2() {
	}
private:
	int a = 4;
};

int main() {
	B a;
	return 0;
}

生成可执行文件ida反编译如下:

main

int __cdecl main(int argc, const char **argv, const char **envp)
{
  char v4[24]; // [rsp+0h] [rbp-30h] BYREF
  unsigned __int64 v5; // [rsp+18h] [rbp-18h]

  v5 = __readfsqword(0x28u);
  B::B((B *)v4);
  B::~B((B *)v4);
  return 0;
}

B::B()

void __fastcall B::B(B *this)
{
  A::A(this); //先构造父类
  *(_QWORD *)this = off_3D68; // 3D68这个位置就是B类的虚函数表,将B类的虚函数表赋给this指针指向的第一个内存块
    /*
    .data.rel.ro:0000000000003D68 off_3D68        dq offset _ZN1A5vir_1Ev ; DATA XREF: B::B(void)+19↑o
	.data.rel.ro:0000000000003D68                                         ; B::~B()+C↑o
	.data.rel.ro:0000000000003D68                                         ; A::vir_1(void)
	.data.rel.ro:0000000000003D70                 dq offset _ZN1B5vir_2Ev ; B::vir_2(void)
    */
  *((_DWORD *)this + 4) = 4;
  std::operator<<<std::char_traits<char>>(&std::cout, "B\n");
}

A::A()

void __fastcall A::A(A *this)
{
  *(_QWORD *)this = &off_3D88; // 3D88是A类的虚函数表
    /*
    .data.rel.ro:0000000000003D88 off_3D88        dq offset _ZN1A5vir_1Ev ; DATA XREF: A::A(void)+C↑o
	.data.rel.ro:0000000000003D88                                         ; A::~A()+C↑o
	.data.rel.ro:0000000000003D88                                         ; A::vir_1(void)
    */
  std::operator<<<std::char_traits<char>>(&std::cout, &unk_2005);
}

B::~B()

void __fastcall B::~B(B *this)
{
  *(_QWORD *)this = off_3D68; //析构时再次赋予虚函数表
  std::operator<<<std::char_traits<char>>(&std::cout, "~B\n");
  A::~A(this);
}

A::~A()

void __fastcall A::~A(A *this)
{
  *(_QWORD *)this = &off_3D88; //析构时再次赋予虚函数表
  std::operator<<<std::char_traits<char>>(&std::cout, &unk_2008);
}

由以上看类中的内容是储存在ptr + 1之后的，第一个用于储存虚函数表的地址。

ref: https://www.cnblogs.com/qg-whz/p/4909359.html

基本原则

C++98 类的基本三大原则

类的构造
类的析构
类的复制

若c++98中,不想复制的话,把构造函数设为私有变量, 并不实现构造函数
不然编译器会自动生成一个对应的构造函数

C++11 类的基本五大原则

前面三点基于c++98，增加了两个原则

5 可以对拷贝构造函数和operator=进行右值引用进行重载

也就是采用左值或者右值进行构造,编译器会对不同的构造函数进行构造.

代码例子

#include <iostream>
#include <string>
#include <vector>
#include <cstring>
#include <cassert>
class RuleOfFive;  //前置声明class
class Parent;
class Child {
	public:
		explicit Child(Parent *p) : m_parent(p) {}
	private:
		Parent *m_parent;
};
class Parent {
	public:
		//                           等同于: m_children.push_back(child)
		bool addChild(Child* child) {m_children.emplace_back(child); }
	private:
		std::vector<Child*> m_children;

};
//若c++98中,不想复制的话,把构造函数设为私有变量, 并不实现构造函数
//不然编译器会自动生成一个对应的构造函数
//c++11 中: RuleOfThree(const RuleOfThree& other) = delete;
class RuleOfThree {
	public:
		RuleOfThree(const char* arg) : cstring(new char[std::strlen(arg) + 1]){ //allocate
			std::strcpy(cstring, arg); //populate	
		}
		~RuleOfThree() {
			delete[] cstring;	
		}
		//c++ 11中,声明该构造不能用, 以防编译器自动生成一个构造函数
		RuleOfThree(const RuleOfThree& other)  = delete;
		//	{//copy constructor
		//		cstring = new char[std::strlen(other.cstring) + 1];
		//		std::strcpy(cstring, other.cstring);
		//	}
		RuleOfThree& operator = (const RuleOfThree& other) {
			char *tmp_cstring = new char[std::strlen(other.cstring) + 1];	
			std::strcpy(tmp_cstring, other.cstring);
			delete[] cstring;
		}
	private:
		char* cstring;

};
//c++11
//类的５大基本原则:
//采用左值或者右值进行构造,编译器会对不同的构造函数进行构造.
class RuleOfFive {
	public:
		//只能针对与右值进行构造
		RuleOfFive(RuleOfFive&& rhs) {
			std::cout << "右值构造.." << std::endl;
			std::cout << rhs.m_value;
			m_value = rhs.m_value;
			rhs.m_value = nullptr;
		};
		RuleOfFive() : m_value(new int(10) ) {}
		//采用右值或者左值进行构造
		RuleOfFive(const RuleOfFive &rhs) : m_value(new int(* (rhs.m_value))) {
			std::cout << "左值或者右值构造.." << std::endl;
		}
		RuleOfFive& operator = (const RuleOfFive &rhs) {
			delete m_value; //删掉以前的
			*m_value = *(rhs.m_value);
			return *this;
		}
		//对= 操作符进行右值重载
		RuleOfFive& operator=(RuleOfFive&& rhs) {
			m_value = rhs.m_value;	
			rhs.m_value = nullptr;
			return *this;
		}
		void print() const {
			assert(m_value && "class print: "); //不推荐使用if来判断
			std::cout << "value: " << *m_value << std::endl;
		}
		~RuleOfFive() { delete m_value; }
	private:
		int *m_value;
};
//左值和右值的定义:
//1. 能够取到地址的值称为左值,否则为右值
void leftOrRight() {
	int a = 0;
	int b;
	int c = 2 + 3;
	int d = a + c;
	auto address = &a;
	//auto address2 = &(2 + 3);
	int& e = a; //左值引用
	//int& e2 = 3; //错误
	int&& e3 = 3; //右值引用.
}
//c++11增加了左值和右值的概念, 所以类的从３大基本原则变为了5大基本原则
void leftAndRight() {
	std::vector<int> a; //left
	for(int i = 0; i < 10; ++i) a.push_back(i);
	auto b = a; //b as left value
	auto &c = b; //c as left value
	//std::vector<int>& c = b; //c as left value
	//move函数啥也不干,就是让编译器把b转换为右值.
	auto d = std::move(b);//std::move(b) 就为右值了
	RuleOfFive f;
	RuleOfFive g(f); //左值构造
	RuleOfFive h (std::move(f)); //右值构造, f已经毫无意义
//	f.print(); //m_value 已经为nullptr
}

int main(void) {
	leftAndRight();
	return 0;
}

STL

STL 是一个框架, 将数据结构和算法进一步的抽象, 包含了容器, 迭代器, 算法
容器: 储存数据的

迭代器: 容器之间统一的一个查询元素接口，可以用来遍历容器的元素

算法: 查找, 排序, 修改…

类别

1 序列式容器 array / vector / deque/list / forward_list 一般实现方式: 数组 ,指针链表
2 关联类有序容器 set / map / multiset / multimap 实现方式: 二叉树, 红黑树
3 关联类无序容器 unordered_map / unordered_set / unordered_multimap / unordered_multiset 实现方式: hash table, 哈希表
4 其他容器: stack / queue / priority_queue / string / bitset (存储对或错)

新型: regex (正则表达式), 增强了 rand算法, thread(线程), async, furture, time

容器内元素的条件

必须可以复制(copy) 或则搬移(move) (隐含的条件是在拷贝和搬移的过程中应该没有副作用)
c++ 的基本类型满足以上要求: bool char int int* char*, reference
元素必须可以被赋值操作,来作为复制或者搬移, (因为容器和算法对复写有要求)
元素可以被销毁

针对于不同的容器还有特殊的要求

对于序列式容器, 元素必须有默认的构造函数
对于某些操作,元素需要定义 ==
对于关联式容器, 排序默认准则的是 <
无顺序容器,必须要提供一个hash函数

stl容器里面存的是元素的值而不是引用，到底我们的容器里面应该存的东西是什么呢?

STL对于错误怎么处理
我们要记住的是STL的设计原则是: 效率优先, 安全为次
异常? STL自己却不怎么用

实例代码

#include <iostream>
#include <chrono>
#include <algorithm>
#include <list>
#include <map>
#include <random>
#include <set>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include <deque>
//多数容器共有的接口:
template<typename T>
void containerAllInterface(T &a, T &b) {
	T c;
	T d(a); //copy
	T e = a; //copy
	T ee {a}; //copy
	T eee = {a}; //copy
	T f(std::move(a)); //move不是转化为右值,是移动数据
	//new
	auto iterB = b.begin();
	auto iterE = b.end();
	//old
	typename T::iterator iterF = b.begin();

	T g(b.begin(), b.end()); //从开始的地方到结束的地方进行拷贝
	T g2(iterB, iterE); //使用迭代器方式,一样


	b.size(); //std::forwad list 不提供size接口,绝大多数都有
	b.empty();  //return b.size() == 0;
	b.max_size();
	if(b == c) {} //先比较数量, 再比较顺序
	if(b != d) {} //
	if(b < e) {}  //unordered_set unordered_map .. 无顺序容器没有
	// b <= e	
	// b > e
	// b >= e
	//赋值
	e = b;
	e = std::move(b);

	e.swap(g); //交换容器所管理的资源, std::arrary 的交换为线性, O(n), 而其他是 O(1)
	//所以其他容器交换很高效,除了array
	std::swap(e, g); //与以上一样

	e.cbegin(); //const_iterator, 返回const iterator的引用
	auto ea = e.cbegin();
	auto eea = e.cbegin();
	*eea; //const &, &
	*ea; // const &
	e.cend();
	e.clear(); //清空容器的所有元素, 有一个容器没有. std::array
	//就是调用所有元素的析构.
}
void test_container() {
	std::vector<int> a;
	std::vector<int> b;
	containerAllInterface<std::vector<int>>(a, b);

	std::list<int> e;
	std::list<int> f;
	containerAllInterface<std::list<int>>(e, f);

	std::deque<int> g;
	std::deque<int> h;
	containerAllInterface<std::deque<int>>(g, h);

	//.......
	//? array, forward_list, unordered_...
}
int main(int, char**) {
	return 0;
}

vector

vector 是c++98中引入的动态数组(dynamic array)

namespace std {
template<typename T, typename Allocator = allocator<T>> //就是用默认的alloctor了,
	class vector;
}

特点

随机访问元素, 末端添加删除元素效率最高, 前端和中间删除和添加元素效率最低，存在当前容器大小和容量的关系

#include <vector>
#include <iostream>
#include <cstring>
//#include <memory>
static void vectorPart() {
using Group = std::vector<float>;
Group a;
Group b = a; //拷贝构造
Group c(a); //拷贝构造
Group d(10); //定义容量的大小
Group e(10, 1.0f); //10个初始化为1.0
Group f(e.begin(), e.end()); //传入两个迭代器,中间的所有值都会被拷贝
Group g({1.0f, 2.0f, 3.0f}); //c++11, 把写好的元素直接填
Group h = {1.1f, 2.1f, 3.1f};
Group i {1.2f, 2.2f, 3.2f, 4.2f}; //initialize list

d.empty();
d.size(); //当前的大小
d.max_size(); //max_size()相对于其他容器的要小一些
d.capacity(); //最多能在装入多少个元素,前提没有分配内存的情况下.
d.reserve(100); //预先分配100个内存空间
d.shrink_to_fit(); //c++11 

//operator == != < > <= >=

//赋值
b = g;
b.assign(3, 1.0f); //代表重新分配元素为: {1.0f, 1.0f, 1.0f}
b.assign(g.begin(), g.end());
b.assign({1.0f, 2.0f, 3.0f});

//交换: 交换给vector类中的指针,效率比较高
b.swap(a);
std::swap(a, b); 

//元素访问:
b[0];
b.at(0); //越界抛出异常: std::out_of_range
if(b.empty()) {
	b.front(); //一定要检查, 不然会出现错误, undefined
	b.back();

}
b.front();
b.back();

//迭代器相关:
a.begin();
a.end();
a.cbegin();
a.cend();
a.rbegin();
a.rend();
a.crbegin();
a.crend();

//
//去除最后一个元素
//signal thread OK, multthread maybe wrong
a.pop_back(); //maybe wrong

//删除某个特定位置的元素
b.erase(b.begin()); //删除掉迭代器当前位置的元素, 而后面的元素会往前移动, 返回下一个元素的位置
b.erase(b.begin(), b.end()); //删除掉迭代器中间元素
//要检查迭代器是否失效

b.push_back(10.0f); //尾部插入元素
b.pop_back(); //获取尾部元素,且释放

//在某个位置插入元素
//在尾部插入100.0
auto iter = b.insert(b.end(), 100.0f); //返回插入元素所在的迭代器
iter = b.insert(b.end(), 10, -10.0f); //在尾部插入10个 -10.0f
b.insert(b.end(), h.begin(), h.end()); //在尾部插入 两个迭代器之间的元素

b.emplace(b.end(), 10.0f); //c++11
b.emplace_back(10.0f); //c++11  && move copy 右值 拷贝

b.resize(10); //设置vector的大小
// 若改变小了,就会调用元素相应的析构
b.resize(100, 1.0f); //把vector的大小设置为100,若元素个数不足100,以值为:1.0来填充到100
b.clear(); //注意: 并不会让以前所占的内存降低, 只是可以把空间腾出来
b.shrink_to_fit(); //c++11, 降低内存到合适的大小

//和C的接口互用
std::vector<char> carr(100, 0);
strcpy(&carr[0], "hello World\n"); //最好用 carr.data();
printf("%s", carr.data());
//错误用法:
printf("%s", carr.begin());

//异常:
//1. push_back
//2. 元素 move / copy 没有异常的话
//insert
//emplact
//emplce_back
//push_bakc
//pop_back
//erase
//swap
//clear　都不会有异常

//特殊:
//标准化的失误:  不要使用,std::vector<bool>
}
int main(int, char**) {

	return 0;
}

deque

deque是c++98中引入的动态数组(dynamic array)

namespace std {
template<typename T, typename Allocator = allocator<T>>
class deque;
}

特点

随机访问元素, 末端和头部添加删除元素效率高,中间删除和添加元素效率低，而vector仅仅操作尾部效率高，元素的访问和迭代比vector要慢,迭代器不能是普通的指针。

#include <deque>
#include <vector>
using Group = std::deque<float>;
static void dequePart() {
Group a;
Group b = a;
Group c(a);
Group d(10);
Group e(10, 1.0f);
Group f(e.begin(), e.end());
Group g({1.0f, 2.0f, 3.0f});
Group h = {1.0f, 2.0f, 3.0f};
Group i {1.0f, 2.0f, 3.0f};

if(!a.empty()) a.pop_back();

d.empty();
d.size();
d.max_size();

//和vector不同, deque不提供以下的函数 
//d.capacity();
//d.reserve(100);
d.shrink_to_fit(); //c++11

//交换
b.swap(a); 
std::swap(a, b);

//元素访问
b[0];
b.at(0);
b.front();
b.back();

//迭代器相关
a.begin();
b.end();
a.cbegin();
a.cend();
a.rbegin();
a.rend();
a.crbegin();
a.crend();


a.pop_back();
a.push_back(1.0f);
a.push_front(1.2f); //vector没有
b.emplace_front(1.0f);


auto iter = b.insert(b.end(), 100.0f); //在某个位置插入元素
b.insert(b.end(), 10, -10.0f);
b.insert(b.end(), h.begin(), h.end());
b.emplace(b.end(), 10.0f);
b.emplace_back(10.0f);
b.resize(10);
b.resize(100, 10.0f);
b.clear();
b.shrink_to_fit(); //释放适当的内存

//异常
//1 push_back push_front 不会抛出异常
//2 move /copy 没有异常的话
//insert emplace emplace_back push_back emplace_front
//pop_back pop_front erase swap clear　不会抛出异常

//应用场景: 可以来储存网络消息的连聊天包机制,分别发包机制
//using Buffer = std::vector<char>;
//using BufferGroup = std::deque<Buffer>;
//BufferGroup group;
//Buffer buffer;
//
//auto ok = readFromClinet(socket, &buffer);
//if(ok) {
//	group.emplace_back(std::move(buffer));
//}else {
//	//handle error
//}
//while(!group.empty()) {
//	auto ok = sendToClient(socket, group.front());
//	if(ok) {
//		group.pop_front();	
//	}else {
//		//handle error	
//	}
//}

}
int main(void) {

	return 0;
}

list

list 是c++98中引入的双向串列(double linked list)

namespace std {
template<typename T, typename Allocator = allocator<T>>
class list;
}

特点

不支持随机访问元素,访问头部和尾部元素快
任何位置插入删除元素都很快,常亮时间内完成
插入和删除不会造成迭代器的失效
对于异常支持好, 出现异常对于list而言, 要么不成功, 要么没有影响

#include <list>
#include <cassert>
#include <iostream>
static void listPart() {
using Group = std::list<float>;

Group a;
Group b = a;
Group c(a);
Group d(10);
Group e(10, 1.0f);
Group f(e.begin(), e.end());
Group g({1.0f, 2.0f, 3.0f});
Group h = {1.0f, 2.0f, 3.0f};
Group i {1.0f, 2.0f, 3.0f};

d.empty();
d.size();
d.max_size();
//和vecotr不同, list不提供以下函数
//d.capacity();
//d.reserve(100);
//d.shrink_to_fit();

// operator == != < > <= >=
//赋值
b = g;
b.assign(3, 1.0f);
b.assign(g.begin(), g.end());
b.assign({1.0f, 2.0f, 3.0f});

//交换
b.swap(a);
std::swap(a, b);

//元素访问, 不能随机访问
//b[0];
//b.at(0);
b.front();
b.back();

//迭代器相关:
a.begin();
a.end();
a.cbegin();
a.cend();
a.rbegin();
a.rend();
a.crbegin();
a.crend();

a.resize(10);
auto iterBegin = a.begin();
assert(a.size() >= 10);
//for(int i = 0; i < 5; ++i) ++iterBegin; //改变迭代器
std::advance(iterBegin, 0); //改变迭代器位置2
//遍历元素
for(; iterBegin != a.end(); ++iterBegin) std::cout << *iterBegin << " ";

a.pop_back(); //maybe wrong
if(!a.empty()) a.pop_back();

b.erase(b.begin());
b.erase(b.begin(), b.end());

b.push_back(10.0f);
b.pop_back();
b.push_front(1.2f);
b.emplace_front(1.3f);

auto iter = b.insert(b.end(), 100.0f);
iter = b.insert(b.end(), 10, -10.0f);

b.resize(5);
b.resize(10, 1.2f);

//算法:
b.remove(1.0f); //删除值为1.0f的所有值
//符合某个条件的值把它删除掉, 100.0f的值全部删除掉
b.remove_if([](auto v) { return v > 100.0f; }); //v 是list中元素的值
b.reverse(); //反转list
b.sort(); //默认以 < 

b.merge(g); // 合并两个排好顺序的list在b中,并清空g中的元素,结果b中就也是排好序的
c.unique(); // 前提: 将排好序的list重复的元素去掉
c.splice(c.begin(), b); //在某个位置插入整块的list, 把b作为一块插入c.begin().

}
int main(void) {
	listPart();
	return 0;
}

forward_list

//forward_list 是c++11中引入的单项串列(singal linked list)

namespace std {
template <typename T, typename Allocator = allocator<T>>
class forward_list;
}

特点

不支持随机元素访问, 访问头部元素速度快，”forward_list” 和自己手写的c-style signal linked list相比没有任何时间和空间上的额外开销, 任何性质如果和这个目标抵触,我们就放弃该特征.任何位置插入和删除元素都很快, 常亮时间完成。插入和删除不会造成迭代器失效，对于异常支持好, 出现异常对于forward_lit而言, 要么不成功, 要么没什么影响。

#include <forward_list>
#include <iostream>
static void forwardListPart() {
using Group = std::forward_list<float>;

Group a;
Group b = a;
Group c(a);
Group d(10);
Group e(10, 1.0f);
Group f(e.begin(), e.end());
Group g({1.0f, 2.0f, 3.0f});
Group h = {1.0f, 2.0f, 3.0f};
Group i {1.0f, 2.0f, 3.0f};

d.empty();
//d.size(); //没有size() ,为了效率
d.max_size();
//和vector不同, forward_list不提供以下函数:
//d.capacity();
//d.reserve(100);
//d.shrink_to_fit();

//operator == != < > <= >=

//赋值
b = g;
b.assign(3, 1.0f);
b.assign(g.begin(), g.end());
b.assign({1.0f, 2.0f, 3.0f});

//交换:
b.swap(a);
std::swap(a, b);

//元素访问, 不能随机访问
//b[0];
//b.at(0);
b.front();
//b.back(); 没有提供最后一个

//迭代器相关
a.begin();
a.end();
a.cbegin();
a.cend();
a.before_begin(); //返回第一个元素的前一个位置, 这个位置只是个占位符
a.cbefore_begin();  //const &
//a.rbegin();
//a.rend();
//a.rcbegin();
//a.rcend();

auto iterBegin = a.begin();

//a.pop_back(); 
a.empty();

//b.erase(b.begin()); //不支持erase
b.erase_after(b.begin()); //删除b.begin(), 的下一个元素 
b.erase_after(b.before_begin()); //return void //正确删除第一个元素 
b.erase_after(b.begin(), b.end()); //return void

//b.push_back(10.0f)
//b.pop_back();

b.push_front(1.2f);
b.emplace_front(1.3f);

//b.insert(b.begin(), 3.0f); 不支持insert

auto iter = b.insert_after(b.before_begin(), 100.0f);
iter = b.insert_after(b.before_begin(), 10, -10.0f);
b.insert_after(b.before_begin(), h.begin(), h.end());

//b.emplace(b.end(), 10.0f);
//b.emplace_back(10.0f);
b.resize(10);
b.resize(100, 1.0f);
//算法:
b.remove(1.0f);
b.remove_if([](auto v) { return v > 100.0f; });
//b.reverse(); //1 2 3 4 -> 4 3 2 1
//std::sort(a.begin(), a.end());
b.sort(); // <
g.sort();
b.merge(g); //对于排好顺序的list进行合并,且合并后也是排好顺序的
c.unique(); //对于排好序的进行删除重复元素
c.splice_after(c.before_begin(), b);


}
int main(void) {
//例:在索引为3的位置之前插入一个元素
	std::forward_list<int> forlist = {1, 2, 3, 4, 5, 6};
	auto fiter = forlist.before_begin();
	for(int i = 0; i < 2; ++i, ++fiter);
	forlist.insert_after(fiter, 10);
	for(fiter = forlist.begin(); fiter != forlist.end(); ++fiter) std::cout << *fiter << " " ;
	std::cout << std::endl;

	return 0;
}

array

array 实际上是对c/c++语言中的原生数组进行了封装

namespace std {
template<typename T, size_t N>
	class array;
}

特点

内存分配在栈(stack), 绝不会重写分配.随机访问元素

#include <iostream>
#include <array>
#include <cstring>

//c++ 11
template<typename C>
void checkSize(C &c) {
	if(c.size() > 3) {
		c[3] = 10; //单线程OK,多线程可能出错
	}
	c.at(3) = 10;
}

void arrayPart() {
	std::array<int, 100> a; //不进行初始化, 只管分配内存
	std::array<int, 100> b = {}; //初始化为 0 
	//以上两者的区别.

	std::array<int, 5> obj = {1, 2, 3, 4, 5};
	std::array<int, 5> obj2 = {1}; //第一个为1, 后面不0

	//接口
	a.empty(); //never be true if size > 0
	a.size();
	a.max_size();

	//operator == < != > <= >=
	auto aa = a;
	aa.swap(a); //array的swap是交换每一个元素都需要做交换,因为它是在stack中储存的.不是通过堆来管理
	//访问元素
	a[1]; //不进行检查,越界出错
	a.at(1); //进行检查,越界抛出异常
	a.front(); //返回头部元素的引用
	a.back();  //返回最后元素的引用
	checkSize(a);

	//迭代器相关的:
	a.begin(); //可以对begin减引操作, 但不能堆end进行此操作
	a.end();
	a.cbegin(); //const　引用
	a.cend();
	
	a.rbegin(); //从尾部遍历到头部,与以上相反
	a.rend();

	a.crbegin(); //const 方式从尾部遍历到头部
	a.crend();


	//和C的接口互用
	std::array<char, 100> carr;
	strcpy(&carr[0], "hello world\n");
	printf("%s", &carr[0]); //更好的使用 carr.data();
	printf("%s", carr.data());
	//错误用法
	printf("%s", carr.begin());


	//特殊的地方
	auto info = std::get<1>(carr); //与 carr[1] 一样
	printf("%c\n", info); //
	carr.fill(0); //对所有元素赋予0

	//异常 exception
	//c.at(pos)
	//copy move swap, 进行操作时,可能触发异常

}
int main(void) {
	arrayPart();
	return 0;
}

C++中的补码公式与位域

补码公式

-x = x+1 = ~(x-1)
~x = -x-1
-(x) = x+1
~(-x) = x-1

实例代码

#include <iostream>
using namespace std;

void operator_1(void);
void operator_2(void);
void operator_3(void);
int main(void) {

        operator_1();
        operator_2();
        operator_3();
        return 0;
}
void operator_1(void) {
        int x = 1;
        cout << "-x = " << -x << "   ~x+1 = " << ~x + 1 << endl;
        cout << "~x = " << ~x << "   -x-1 = " << -x - 1 << endl;
        cout << "-(~x) = "<< -(~x) << "   x+1 = " << x + 1 << endl;
        cout << "-(~x) = "<< -(~x) << "   x-1 = " << -x -1 << endl;
}
void operator_2(void) {
        int x = 3, y = 5;
        cout << endl;
        cout << "x: " << x << "y: " << y << endl;
        cout << "x+y=" << x+y << "   x- ~y-1= " << x - ~y - 1
        << "  (x|y)+(x&y) = " << (x|y) + (x&y) << endl;
        cout << "x-y=" << x-y << "   x+ ~y+1= " << x + ~y + 1
        << "  (x|~y) - (~x&y) = " << (x|~y) - (~x|y) << endl;

        cout << "x^y=" << (x^y) << " (x|y) - (x&y)" << (x|y) - (x&y) << endl;
        cout << "x|y=" << (x|y) << " (x& ~y) + y = " << (x& ~y) + y << endl;
        cout << "x&y=" << (x&y) << " (~x|y) - ~x = " << (~x|y) - ~x << endl;
}
void operator_3(void) {
        int x = -3, y = -5;
        unsigned int x_t = -1, y_t = -5;
        cout << "x: " << x << "y: " << y << endl;
        cout << "x==y =" << (x==y) << "  ~(x-y|y-x) =" << ~(x-y|y-x) << endl;
        cout << "x!=y =" << (x!=y) << "  x-y|y-x =" << (x-y|y-x) << endl;
        cout << "x<y =" << (x<y) << "  (x-y) ^ ((x^y) & ((x-y)^x))=" << ((x-y) ^ ((x^y) & ((x-y)^x))) << endl;
        cout << "x<=y =" << (x<=y) << "  (x|~y) & ((x^y) |~ (y-x))=" << ((x|~y) & ((x^y) |~ (y-x))) << endl;
        cout << "unsigned: x<y =" << (x_t<y_t)
        << "  (~x&y) | ((~x|y) & (x-y))" << ((~x_t&y_t) | ((~x_t|y_t) & (x_t-y_t))) << endl;

        cout << "unsigned: x<=y =" << (x_t<=y_t)
        << " (~x|y) & ((x^y) | ~(y-x) =" << ((~x_t|y_t) & ((x_t^y_t) |~ (y_t-x_t))) << endl;

}

位域

在结构内声明位域的形式如下：

struct
{
  type [member_name] : width ;
};

下面是有关位域中变量元素的描述：

元素	描述
type	只能为 int(整型)，unsigned int(无符号整型)，signed int(有符号整型) 三种类型，决定了如何解释位域的值。
member_name	位域的名称。
width	位域中位的数量。宽度必须小于或等于指定类型的位宽度。

实例代码

#include <stdio.h>
typedef struct bs {
        int a:2;
        int b:1;
        int c:12;
        unsigned d:4
}bs;
struct bit_2 {
        unsigned a:2;
        unsigned :2;  //It can't use
        unsigned :0;  //NULL
        unsigned b:4;
        unsigned c:4;

};
int main(void) {
        bs bit;
        printf("sizeof(%d) \n",sizeof(struct bs));
        bit.a = 4;
        bit.b = 1;
        bit.c = 34235;
        printf("a: %d   b: %d  c: %d\n", bit.a, bit.b, bit.c);

        return 0;
}

lambda

#include <functional>
#include <iostream>
//基础函数
void printInfo(int a, int b, int c) {
			std::cout << " a " << a << " b " << b << " c " << c << std::endl;
}

//操作符重载函数
struct Print {
	void operator() (int a, int b, int c) const {
			std::cout << " a " << a << " b " << b << " c " << c << std::endl;
	}
};
//模板函数
template<typename T1, typename T2, typename T3>
void templatePrint(T1 a, T2 b, T3 c) {
			std::cout << " a " << a << " b " << b << " c " << c << std::endl;
}

//操作符重载 + 模板 的函数
struct TemplatePrint {
	template<typename T1, typename T2, typename T3>
		void operator() (T1 a, T2 b, T3 c) const {
			std::cout << " a " << a << " b " << b << " c " << c << std::endl;
	}
};

inline void print(int a, int b, int c) {
	std::cout << " a " << a << " b " << b << " c " << c << std::endl;
}
template<typename Fun>
void printUseFun(Fun fun, int a, int b, int c) {
	fun(a, b, c);
}
void test_1() {
	Print printUseClass;	
	TemplatePrint printUseTempClass;

	printInfo(1, 2, 3);
	printUseClass(1, 2, 3); //operator() (int a, int b, int c)

	templatePrint(1, 2, 3); 
	printUseTempClass(1, 2, 3);
	print(1, 2, 3);

	//以前inline 函数跟普通函数调用差不多
	//lambda就是个inline函数, 只是把 inline 函数作为一个参数或者一个local变量来使用, 

	std::cout << "lamda: " << std::endl;
	auto local = [](int a, int b, int c) {
		std::cout << " a " << a << " b " << b << " c " << c << std::endl;
	};
	printUseFun(local, 1, 2, 3);
	printUseFun([](int a, int b, int c) {
		std::cout << "lamda2:" << std::endl;	
		std::cout << " a = " << a << " b = " << b << " c = " << c << std::endl;
	}, 2, 3, 5);

	int a = 6, b = 7, c = 8;

	auto local2  = [a, b, c]() {
		std::cout << " a = " << a << " b = " << b << " c = " << c << std::endl;
	};
	local2();

	auto local3 = [=]() {
		std::cout << "====" << std::endl;
		std::cout << " a = " << a << " b = " << b << " c = " << c << std::endl;
	};
	local3();

	auto local4 = [=]() mutable {
		std::cout << "====" << std::endl;
		a = 4, b = 4 , c = 4;
		std::cout << " a = " << a << " b = " << b << " c = " << c << std::endl;
	};
	local4();
	
}
int main(void) {
	test_1();
	return 0;
}

C++11新型for循环,auto, 类成员的初始化及左右值引用

C++11中新型for循环,auto, 类成员的初始化及左右值引用

#include <typeinfo>
#include <iostream>
#include <string>
#include <vector>
#include <iterator>

static void autoValue();
static void autoPointer();
static void newVersionFor();
static void newVersionConstruct();
static void defaultInitValue();
static void leftRefAndRightRef();

//自定义类实现新型for循环
class MyVector {
	public:
		using GroupType = std::vector<int>;
	public:
		GroupType m_group;
		void push_back(int x) {
			m_group.push_back(x);
		}
};

MyVector::GroupType::iterator begin(MyVector &v) {
	return v.m_group.begin();
}
MyVector::GroupType::iterator end(MyVector &v) {
	return v.m_group.end();
}
void testMyClass() {

	MyVector mv;
	mv.push_back(1);
	mv.push_back(2);
	mv.push_back(3);
	for(auto i : mv) {
		std::cout << i << " ";	
	}
	std::cout << std::endl;
}


int main(int /*argc*/, char** /*argv*/) {
	testMyClass();
	//new version auto
	//autoValue();
	//autoPointer();
//	newVersionFor();
	//newVersionConstruct();
//	defaultInitValue();
	leftRefAndRightRef();
	return 0;
}

static void autoValue() {
	auto age = 10;
	auto name = std::string("Yt");
	auto height = 160.0f;
	auto wight = 72.0;
	std::cout << "age is type " << typeid(age).name() << std::endl;
	std::cout << "name is type " << typeid(name).name() << std::endl;
	std::cout << "height is type " << typeid(height).name() << std::endl;
	std::cout << "weight is type " << typeid(wight).name() << std::endl;
}
static void autoPointer() {
	auto age = new int(10);
	auto name = "Yt";
	auto height = new float(160.0f);
	auto wight = new double(72.0);

	std::cout << "age is type " << typeid(age).name() << std::endl;
	std::cout << "name is type " << typeid(name).name() << std::endl;
	std::cout << "height is type " << typeid(height).name() << std::endl;
	std::cout << "weight is type " << typeid(wight).name() << std::endl;
}
static void newVersionFor() {
	int ids[] = {1, 2, 3, 4, 5};
	std::cout << "new version";
	for(auto v : ids) {
		std::cout <<  v << " ";	
	}
	std::cout << std::endl;

	std::cout << "old version";

	for(int i = 0; i < sizeof(ids) / sizeof(ids[0]); ++i) {
		std::cout << ids[i] <<  " ";	
	}
	std::cout << std::endl;

	//vector::
	std::vector<int> group;
	for(int i = 0; i < 4; ++i) group.push_back(i);
	//old version:
	//老版本遍历方式 
	for(std::vector<int>::size_type i = 0, size = group.size(); i < size; ++i) {
		//cout << group[i] << " ";	
	}
	//通过迭代器来遍历
	std::cout << "iterator: " << std::endl;
	//-------对于迭代器自增的时候,要用前置操作符,不要用后置操作符. ++iter, 若使用后置操作符号
	//多了一个步骤,就是把自增前的值先保留起来, 然后在自增.无用功
	for(std::vector<int>::const_iterator iter = group.begin(); iter != group.end(); ++iter) {
		std::cout << *iter << " ";	
	}

	std::cout << std::endl;
	//auto version
	std::cout << "vector old version:" << std::endl;
	for(auto v : group) {
		std::cout << v << " ";
	}

	std::cout << std::endl;
	std::cout << "vector new version:" << std::endl;
	for(auto &v : group) {
		v = 1;
	}
	for(const auto &v : group) {
		std::cout << v << " ";
	}
}

class A {
	public:
		//why explicit ?? 具体含义是什么?
		explicit A(int value) : m_value(value) { }

	private:
	int m_value;
};

static void newVersionConstruct() {

	A a(10);
	A b{3};

	//old
	int avector[] = {1, 2, 3};
	std::vector<int> bv;
	for(auto v : avector) bv.push_back(v);
	
	//new 
	std::vector<int> cv = {1, 2, 3};
	std::vector<int> v {1, 2, 3};

	A c(true);
	A d(false);

	A e(1.0);
	// A f{1.0} //不能做构造, 只能提高精度， 不能丢失
}

class B {
	public:
		B() : m_age(18), m_height(170), m_weight(75) {}
		explicit B(int age) : m_age(age), m_height(170), m_weight(75) {}
		B(int age, int height) : m_age(age), m_height(height) {}
		int age() const { return m_age; }
		int height() const { return m_height; }
		int weight() const { return m_weight; }
	private:
		int m_age;
		int m_height;
		int m_weight;
};

class NewB {
	public:
		NewB() {}
		explicit NewB(int age) : m_age {age} {}
		NewB(int age, int height) : m_age{age}, m_height {height} {}
		int age() const { return m_age; }
		int height() const { return m_height; }
		int weight() const { return m_weight; }
		void p() const { std::cout << m_value << " " << m_fightValue;}

	private:
		int m_age = 18; //初始化, 放置出现bug
		int m_height = 170;
		int m_weight = 75;
		int m_value{}; //代表拿int的默认值来作初始化,也就是0
		double m_fightValue{}; //0.0
};

static void defaultInitValue() {
	B a(10, 20);
	NewB b(10, 20);

	std::cout << "Old a age is" << a.age() << "height " << a.height()
		<< " wight " << a.weight() << std::endl;

	std::cout << "New b age is" << b.age() << "height " << b.height()
		<< " wight " << b.weight() << std::endl;

	b.p();
}

static void leftRefAndRightRef() {
	//什么是引用
	//引用类似与指针,　不同之处在于, 指针可以为nullptr, 但引用不可以
	int a = 10;
	int &refA = a;
	const int &constRefA = a;
	std::cout << " a" << a << " ref of a " << refA << " const ref a "
		<< constRefA << std::endl;
	//this is a error
	// int &refB = 10;
	const int &constRefB = 10; //不管左值还是右值,都能赋给const 引用
	std::cout << "different version const ref " << constRefB << std::endl;

	//auto &&rrB = 20; //与下一样
	int &&rrB = 20;
	const int &&crrB = 20;
	
	rrB = 30; //可以改变右值, 其实只是改变那个值而已
	std::cout << " right ref of b " << rrB << " const right ref b "
		<< crrB << std::endl;
	int b = 20;
	int &&newRRB = std::move(b); //强行转为右值
	const int &&cNewRRB = std::move(b);
	std::cout << " b " << b << " right ref of be " << newRRB << "const right ref b "
		<< cNewRRB << std::endl;
	std::cout << "address " << &b << " ref " << &newRRB << " c ref " << &cNewRRB << std::endl;

}

C++11智能指针

目前c++ 的4种指针

auto_ptr c++98 智能指针,使用了
shared_ptr //共享指针
unique_ptr //只能由一个使用者使用
weaked_ptr //与share_ptr搭配使用

shared_patr

实例代码

#include <iostream>
#include <memory>
static void interfaceOfSharedPtr();

int main(void) {
	interfaceOfSharedPtr();
	return 0;
}

class Object {
	public:
		Object(int id) : m_id(id) { std::cout << "init obj " << m_id << std::endl; };
		~Object() { std::cout << "bye bye " << m_id << std::endl; }
		int id() const { return m_id; }
	private:
		int m_id = 0;
};


//使用智能指针
using ObjectPtr = std::shared_ptr<Object>;


//作为参数的obj,相当于拷贝了一次,use_count 会+ 1,但当函数结束时候,智能指针析构,use_count会恢复原来的个数
void print(ObjectPtr obj) {
	//-------------------------智能指针的成员函数
	std::cout << "count " << obj.use_count() << " id " << obj->id() << std::endl;
}
//以引用方式,不会进行copy, use_count不变
void printRef(const ObjectPtr &obj) {
	std::cout << "ref count " << obj.use_count() << "id " << obj->id() << std::endl;
}


static void interfaceOfSharedPtr() {
	ObjectPtr null;
	std::cout << "ref count is " << null.use_count() << std::endl;

	//使用智能指针来储存对象的指针
	ObjectPtr obj (new Object(1));	
	std::cout << "ref count is " << obj.use_count() << std::endl;

	ObjectPtr obj2(obj);
	std::cout << "ref count is " << obj2.use_count() << std::endl;

	ObjectPtr obj3 = obj;
	std::cout << "ref count is " << obj.use_count() << std::endl;

	obj2.reset(); //What dose means of reset ?
	std::cout << "ref count is " << obj.use_count() << std::endl;

	ObjectPtr obj4;
	obj3.swap(obj4); //把obj3的管理资源相互交换
	std::cout << "obj4 ref count is " << obj4.use_count() << std::endl;
	std::swap(obj3, obj4); //采用另一种方式交换 
	std::cout << "obj4 ref count is " << obj4.use_count() << std::endl;

	//把智能指针存储的指针传出来
	auto p = obj.get();
	if(p) {
		std::cout << "id is" << p->id() << std::endl;	
	}
	if(obj) { //重载了 operator bool
		std::cout << "p id is " << obj->id() << std::endl; //重载: operator ->
		std::cout << "ref id is " << (*obj).id() << std::endl; //重载了: operator *
	}
	
	obj4 = nullptr;
	//----------------------------->obj.use_count() == 1 可能效率比较底一点
	std::cout << "only one hold ptr " << obj.unique() << std::endl; //判断是否是一个人在使用
	std::cout << "judge differnt: " << std::endl;
	std::cout << "use_count: " << obj.use_count() << std::endl;
	printRef(obj);
	print(obj);
	std::cout << "use_count: " << obj.use_count() << std::endl;
}

void deleterOfObject(Object *obj) {
	if(obj)
		std::cout << "delete obj " << obj->id()  << std::endl;
	delete obj;
}

void useDeleter() {
	//当智能指针出了作用域后,析构函数就被调用, 哪怕中途抛出异常
	ObjectPtr obj(new Object(2), deleterOfObject);
	ObjectPtr obj2 = obj;
}

weak_ptr

c++智能指针-shared_ptr的尴尬-诞生weak_ptr

#include <iostream>
#include <memory>
#include <cassert>

//auto ptr
//shared_ptr
//unique_ptr
//weak_ptr

class Parent; //采用前置声明

using ParentPtr = std::shared_ptr<Parent>;
typedef std::weak_ptr<Parent> WeakParentPtr;

class Child {
	public:
//		ParentPtr father; //内存泄露
		WeakParentPtr father; //采用弱指针,则可以释放内存,不造成内存泄露
		Child() { std::cout << "Child!!" << std::endl; }
		~Child();
};

typedef std::shared_ptr<Child> ChildPtr;
typedef std::weak_ptr<Child> WeakChildPtr;

class Parent {
	public:
		Parent() { std::cout << "Parent!!" << std::endl; }
		ChildPtr son;
//		WeakChildPtr son;

		void print() const { std::cout << "use_count: " << this->son.use_count() << std::endl;}
		~Parent();
};

class Object {
	public:
		Object(int id) : m_id(id) { std::cout << "init obj " << m_id << std::endl; };
		~Object() { std::cout << "bye bye " << m_id << std::endl; }
		int id() const { return m_id; }
	private:
		int m_id = 0;
};
using ObjectPtr = std::shared_ptr<Object>;

Child::~Child() { std::cout << "bye child!" << std::endl; }
Parent::~Parent() { std::cout << "bye parent!" << std::endl; }
//----------------------------------------------
void testParentAndChild() {
	ParentPtr p(new Parent());
	ChildPtr c(new Child());

//采用这种方式,造成内存泄露
	p->son = c; //智能指针拷贝, use_count + 1, c 的use_count 为 2
	p->print();
	c->father = p; //p 的 use_count 也为 2 了

//智能指针析构之后use_count  -1
//智能指针特性: 只有当use_count 变为0 时,才能释放掉管理的资源
//所以智能指针析构后,use_count 不为0,则造成了内存泄露
	////////////
//只要打破环状的引用,则share_ptr就会很好的管理内存
}
//----------------------------------------------
//为了解决以上问题, 采用weak_ptr来解决
void sharedPtrWithWeakPtr() {
	ObjectPtr obj(new Object(1));
	typedef std::weak_ptr<Object> WeakObjectPtr;
	WeakObjectPtr weakObj(obj);//弱指针依赖于share_ptr,若share_ptr是有效的,则wake_ptr也是有效的.
	WeakObjectPtr weakObj2(obj);
	//而wake_ptr在进行赋值的操作运算的时候,并不影响use_count, 相当于只是作为监听者

	
	std::cout << "obj use count is " << obj.use_count() << std::endl;
	{
		auto p = weakObj.lock(); //相当于返回了一个 ObjectPtr类型,
		std::cout << "expired: " << weakObj.expired() << std::endl; //expierd() 查看监控的资源过期没有过期
		if(p) {
			std::cout << p.unique() << std::endl; //false, use_count >= 2, 因为auto p = ...,进行了一次指针拷贝, 
			//所以use_count + 1, 而weakObj.lock()返回若是有效的话,则use_count >= 1, 否则返回nullptr
			//则总体的就use_count >= 2
			//do what you wanna do	
		}else {
		
		
		}
	}
	obj.reset(); //obj 放弃管理的资源
	std::cout << "endl;";
	auto p2 = weakObj.lock(); //返回空,因为,obj不管理资源了
	
	obj.reset(new Object(2)); //重新管理另一个资源
	{
		auto p = weakObj.lock();
		if(p) {
			assert(false);
		}else {
			//要么资源已经释放,要么obj管理的资源跟换了.
			std::cout << "changed!" << std::endl;
		}

	}
	std::cout << "expired: " << weakObj.expired() << std::endl; //expierd() 查看监控的资源过期没有过期
}
int main(void) {
	testParentAndChild();
//	sharedPtrWithWeakPtr();
	return 0;
}

shared_ptr储存this指针多次析构问题

enable_shared_from_this解决方案

#include <iostream>
#include <memory>
#include <cassert>
/*
		//this //调用了两次析构函数,
		ParentPtr p(this);
		//智能指针出了作用域后就delete this ,析构了
		//所以错了,为了解决这个问题,就需要自身的类继承于　std::enable_shared_from_this<Type>
		//将ParentPtr p(this) 换成, shared_from_this();
 
 */
class Parent;
typedef std::shared_ptr<Parent> ParentPtr;
typedef std::weak_ptr<Parent> WeakParentPtr;

class Child : public std::enable_shared_from_this<Child> {
	public:
		WeakParentPtr father;
//		ParentPtr father;
		~Child();
		Child();
		void checkRelation();
};

typedef std::shared_ptr<Child> ChildPtr;
typedef std::weak_ptr<Child> WeakChildPtr;

class Parent : public std::enable_shared_from_this<Parent> {
	public:
		WeakChildPtr son;
//		ChildPtr son;
		~Parent();
		Parent();
		void checkRelation();
};

void handleChildAndParentRef(const Parent &p, const Child &c) {
	if(c.father.lock().get() == &p && p.son.lock().get() == &c) {
		std::cout << "right relation" << std::endl;	
	}else {
		std::cout << "oop!!!!!!" << std::endl;
	}
}
void handleChildAndParent(const ParentPtr &p, const ChildPtr &c) {
	assert(c);
	assert(p);
	if(c->father.lock() == p && p->son.lock() == c) {
		std::cout << "right relation" << std::endl;	
	}else {
		std::cout << "oop!!!!!!" << std::endl;
	}
}
Child::Child() { std::cout << "hello child" << std::endl; }
Child::~Child() { std::cout << "bye child" << std::endl; }
Parent::Parent() { std::cout << "hello parent" << std::endl; }
Parent::~Parent() { std::cout << "bye parent" << std::endl; }

void Parent::checkRelation() {
	auto ps = son.lock();
	if(ps) {
		//this //调用了两次析构函数,
//		ParentPtr p(this);
		//handleChildAndParent(p, ps);	

		//智能指针出了作用域后就delete this ,析构了
		//所以错了,为了解决这个问题,就需要自身的类继承于　std::enable_shared_from_this<Type>
		//将ParentPtr p(this) 这种错误形式换成, shared_from_this()
		handleChildAndParent(shared_from_this(), ps);	
	}
		std::cout << "after call checkRelation" << std::endl;
}

void Child::checkRelation() {
	
}
void testParentAndChild() {
	//若Parent 继承于 std::enable_shared_from_this<Type>
	//则 Parent pp; 这种静态的就不推荐
	ParentPtr p(new Parent());
	ChildPtr c(new Child());
	p->son = c;
	c->father = p;
	p->checkRelation();
}

static void interfaceOfSharedPtr();
static void sharedPtrWithWeakPtr();
static void uniquePtr();

int main(void) {
	testParentAndChild();	
	return 0 ;
}

unique_ptr

#include <iostream>
#include <memory>
#include <cassert>

class Object;

typedef std::unique_ptr<Object> UniqueObjectPtr;
using ObjectPtr = std::shared_ptr<Object>;

void print(const UniqueObjectPtr& obj) {}

class Object {
	public:
		Object(int x) : m_id(x) { std::cout << "Hello Obj" << std::endl; };
		~Object() { std::cout << "Bye Obj" << std::endl; };
		int id() { return m_id; }
	private:	
		int m_id = 0;

};
void transfer(UniqueObjectPtr obj) {
	std::cout << obj->id() << std::endl;
}

void uniquePtr() {
	UniqueObjectPtr obj { new Object(1) };
	auto p = obj.get(); //operator bool
	if(p) {
		//do some	
	}
	//better
	if(obj) {
				
	}
	
	std::cout << p->id() << " " << obj->id() << " " << (*obj).id() << " " << std::endl;
	print(obj);
	
	p = obj.release(); //释放所管理的指针
	std::cout << "release: unique_ptr" << std::endl;
	delete p; //直接释放资源

	obj.reset(new Object(2)); //reset 就是将以前所管理的指针释放掉, 管理一个新的指针
	//UniqueObjectPtr (const UniqueObject&) = delete //这种拷贝构造函数不存在
	//UniqueObjectPtr (const UniqueObject&&) = default //
	transfer(std::move(obj)); //采用这种方式传入, 则自己的资源不在管理,而交给了这个参数
	//传入之后, obj 值为null

	assert(obj == nullptr);
//	std::cout << obj->id() << std::endl;

	obj.reset(new Object(3));
	ObjectPtr sharedObj(std::move(obj));
	assert(obj == nullptr);
//boost库
/*
	c++ 智能指针来源于boost库.
	shared_ptr
	weak_ptr
	enable_shared_from_this
	scoped_ptr //与unique_ptr　很类似, 但局限性比较多, 所以c++11没有采用
	unique_ptr
 */
}

int main(void) {
	uniquePtr();
	return 0;
}

智能指针总结

#include <iostream>
#include <memory>
#include <cassert>
void sharedPtrNotice();
class Parent;
typedef std::shared_ptr<Parent> ParentPtr;
typedef std::weak_ptr<Parent> WeakParentPtr;
class Child : public std::enable_shared_from_this<Child> {
	public:	
		WeakParentPtr father;
		Child();
		~Child();
};
class Object {
	public: 
		Object(int x) : m_value(x) { }
	private:
		int m_value = 0;
};
using ObjectPtr = std::shared_ptr<Object>;

void sharedPtrNotice() {
	//1 : 绝对不要自己手动的管理资源 
	//int* a = new int(10);
	//delete a;
	//int *b = malloc(sizeof(int));
	//if(b) free(b);

	//2 :一个裸的指针不要用两个shared_ptr管理, 对于unique_ptr也如此
	//auto pObj = new Object(1);	
	//ObjectPtr obj(pObj);
	//ObjectPtr obj2(pObj);

	//用weak_ptr打破循环引用,parent 和 child
	//当需要在类的内部接口中, 如果需要将this 作为智能指针来使用的话,
	//需要用该类派生自std::enable_shared_from_this
	//
	//使用share_ptr作为函数的接口,如果有可能有const shared_ptr& 的形式
	//多线程模式下使用shared_ptr需注意的事项(....)

	//shared_ptr weak_ptr 和裸指针相比, 会大很多, 并且效率上会有影响.
	//尤其是在多线程模式下

	//shared_ptr 和 weak_ptr彼此互存,智能指针,空间上消耗资源比较大,而且时间效率上也比较低

	//一般情况下 ObejectPtr obj(new Object(2)),　相当于进行了两次new的过程.对于时间和空间上比较消耗
	//官方发现了这个问题,做了如下改正,且实现的功能一样

	//只实现了一次new,将new Object() 和 new 自身的指针归在一起
	ObjectPtr obj5 = std::make_shared<Object>(3); //真正推荐使用...


	//enable_shared_from_this 中shared_from_this()和构造析构函数一样
	//不能在构造或者析构中使用,否则会出错的.

	//某些情况下,会出现内存不会降问题.尤其是使用weak_ptr来处理循环引用问题
	//那是可能因为weak_ptr给勾住了,也要需要weak_ptr释放了,才能解决.

	//如果有可能,优先使用类的实例,其次万不得已 2 使用std::unique_ptr
	//万不得已 3 使用 std::shared_ptr
	Object obj6(4); //优先
	std::unique_ptr<Object> puObj(new Object(1)); //其次
	std::shared_ptr<Object> psObj = std::make_shared<Object>(3); //在其次

}
int main(void) {
	
	return 0;
}

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