Example: std::function and lambda

左手的ㄟ右手 2022-07-24 05:30 194阅读 0赞

之前C++11中写过几篇博客：

**std::function**  
[http://blog.csdn.net/wangshubo1989/article/details/49134235][http_blog.csdn.net_wangshubo1989_article_details_49134235]

**lambda**  
[http://blog.csdn.net/wangshubo1989/article/details/49256795][http_blog.csdn.net_wangshubo1989_article_details_49256795]

**延时求值**  
[http://blog.csdn.net/wangshubo1989/article/details/50465693][http_blog.csdn.net_wangshubo1989_article_details_50465693]

**callback**  
[http://blog.csdn.net/wangshubo1989/article/details/50465693][http_blog.csdn.net_wangshubo1989_article_details_50465693]

**std::placeholders**  
[http://blog.csdn.net/wangshubo1989/article/details/50471709][http_blog.csdn.net_wangshubo1989_article_details_50471709]

用一个例子，再重温一下吧：

写一个Caller类

#include <functional>
    #include <string>
    
    class Caller
    {
        std::function<std::string(int num)> m_numWriter;
    public:
        Caller(std::function<std::string(int num)> writerFunc) : m_numWriter(writerFunc)  {}
    
        std::string WriterForMe(int n){
       return m_numWriter(n); }
    }

main函数：

#include <iostream>
    #include <memory>
    
    int main()
    {
        auto cr = std::unique_ptr<Caller>(new Caller([](int n){
       return string("III");}));
        std::cout << cr->WriterForMe(3) << std::endl;
    
        char ch;
        std::cin >> ch;
        return 0;
    }

**callback in vector**

#include <functional>
    #include <iostream>
    #include <vector>
    
    
        class Test
        {
        public:
              Test (int testType) : m_testType(testType) {};
              void blah() { std::cout << "BLAH! " << m_testType << std::endl; }
              void blahWithParmeter(std::string p) { std::cout << "BLAH1! Parameter=" << p << std::endl; }
              void blahWithParmeter2(std::string p) { std::cout << "BLAH2! Parameter=" << p << std::endl; }
    
              private:
                 int m_testType;
    
        };
    
        class Bim
        {
        public:
              void operator()(){ std::cout << "BIM!" << std::endl; }
        };
    
        void boum() { std::cout << "BOUM!" << std::endl; }
    
    
    int main()
    {
        // store the member function of an object:
        Test test(7);  
    
        std::function< void() > callback = std::bind( &Test::blah, test );
        callback();
    
        // store a callable object (by copy)
        callback = Bim{};
        callback();
    
        // store the address of a static funtion
        callback = &boum;
        callback();
    
        // store a copy of a lambda (that is a callable object)
        callback = [&]{ test.blah(); }; // might be clearer than calling std::bind()
        callback();
    
        // example of callback with parameter using a vector
        typedef std::function<void(std::string&)> TstringCallback;
    
        std::vector <TstringCallback> callbackListStringParms;
        callbackListStringParms.push_back( [&] (const std::string& tag) { test.blahWithParmeter(tag); }); 
        callbackListStringParms.push_back( [&] (const std::string& tag) { test.blahWithParmeter2(tag); }); 
    
        std::string parm1 = "parm1";
        std::string parm2 = "parm2";
        int i = 0;
        //基于范围的for循环
        for (auto cb : callbackListStringParms ) 
        {
            ++i;
            if (i == 1)
                cb(parm1);
            else
                cb(parm2);
    
            }
    }

[http_blog.csdn.net_wangshubo1989_article_details_49134235]: http://blog.csdn.net/wangshubo1989/article/details/49134235
[http_blog.csdn.net_wangshubo1989_article_details_49256795]: http://blog.csdn.net/wangshubo1989/article/details/49256795
[http_blog.csdn.net_wangshubo1989_article_details_50465693]: http://blog.csdn.net/wangshubo1989/article/details/50465693
[http_blog.csdn.net_wangshubo1989_article_details_50471709]: http://blog.csdn.net/wangshubo1989/article/details/50471709