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std::bind（）

std::bind 主要用于绑定生成目标函数，一般用于生成的回调函数，cocos的回退函数都是通过std::bind和std::function实现的。两个点要明白：

1.绑定全局或者静态函数比绑定成员函数少了个成员变量，且不需要引用如下

//绑定全局函数
auto pfunc = std::bind(func1, 3);
//绑定静态函数
pfunc = std::bind(Func::func6, 3);
//绑定类成员函数，函数前需要添加引用，多一个变量参数fuc
Func func;
pfunc =std::bind(&Func::func2,func, 3);

2.占位符std::placeholders::_1代表此处是要输入参数，且这个参数排在第一位，代码分析更明白

#include <iostream>
#include <functional>
using namespace std;
class Func
{
public:
    static void  func6(int numa, int numb, int numc)
	{
		std::cout << numa << " " << numb << " " << numc << endl;
	}
    void func2(int numa, int numb, int numc,std::string name)
	{
		std::cout << numa << " " << numb << " " << numc<<" " << name<< endl ;
	}
}
void callFunc(std::function<void(int a,int b)> call)
 {
	 call(1,2);
 }
 void func1(int numa, int numb, int numc)
 {
	 std::cout << numa << " " << numb << " " << numc << endl;
 }
int main()
{
   callFunc(std::bind(func1, std::placeholders::_1, std::placeholders::_2, 3));
   callFunc(std::bind(func1, std::placeholders::_2, std::placeholders::_1, 3));
   callFunc(std::bind(func1, std::placeholders::_2, 3, std::placeholders::_1));
   callFunc(std::bind(Func::func6, std::placeholders::_1, std::placeholders::_2, 3));
   callFunc(std::bind(&Func::func2, func, std::placeholders::_1, std::placeholders::_2, 3, "name"));
}

运行结果如下

std::function

std::function等于函数指针，相比函数指针使用更方便，记录一下几种用法:指向全局或者静态函数，类成员函数，Lambda表达式和仿函数。指向全局函数或者静态函数时使用std::function<void()> testFunc = func3，指向类成员函数时，需要制定函数所属的类的成员变量testFunc = std::bind(&Func::func2, func, 1, 2, 3, “name”)。代码如下：

#include <iostream>  
#include <string> 
#include <iostream>
#include <functional>
using namespace std;
class Func
{
public:
	int sum;
	Func()
	{
		sum = 2;
	}
	void func2(int numa, int numb, int numc,std::string name)
	{
		std::cout << numa << " " << numb << " " << numc<<" " << name<< endl ;
	}
	void func4()
	{
		std::cout << "func4" << endl;
	}
	void operator() (int a,int b)
	{
		std::cout << "Operator:" << sum<<"  "<<a<<"  "<<b<<endl;
	}
	static void  func6(int numa, int numb, int numc)
	{
		std::cout << numa << " " << numb << " " << numc << endl;
	}
	static void  func5()
	{
		std::cout << "static func" << endl;
	}
};
 void callFunc(std::function<void(int a,int b)> call)
 {
	 call(1,2);
 }
 void func3()
 {
	 std::cout <<"func3"<< endl;
 }
 void func1(int numa, int numb, int numc)
 {
	 std::cout << numa << " " << numb << " " << numc << endl;
 }
int main()
{
	Func func;
	int sum = 10;
	int resultInt = 0;
	//全局或者静态函数
	std::cout << "全局或者静态函数" << endl;
	std::function<void()> testFunc = func3;
	testFunc();
	testFunc = Func::func5;
	testFunc();
	//类成员函数
	std::cout << "类成员函数" << endl;
	testFunc = std::bind(&Func::func2, func, 1, 2, 3, "name");
	testFunc();
	//Lambda表达式
	std::cout << "Lambda表达式" << endl;
	testFunc = [=, &resultInt](){std::cout << sum << endl; resultInt += 100; };
	testFunc();
	cout << "the reslutInt is " << resultInt << endl;
	//仿函数
	std::cout << "仿函数" << endl;
	std::function<void(int a, int b)> abFunc = func;
	abFunc(10, 20);
	std::cout << resultInt << std::endl;
}

运行结果：