c++ lamda 函数

// lamda.h
#include<iostream>
#pragma once
using namespace std;
void funcExt();
class Lamb
{
private:
    int aa =20;
    int bb =30;
public:
    Lamb();
    ~Lamb();
    void show();
    void f()
    {
        auto fun10 = [this]()
        {
            this->show();
        };
        fun10();
    }
};

 

//lamda_ext.cpp
#include "lamda.h"
auto func =[]()
{
    cout<<"funcExt result."<<endl;
};
void funcExt()
{
    func();
}
Lamb::Lamb() {};
Lamb::~Lamb() {};
void Lamb::show()
{
    cout<<aa+bb<<endl;
}

 

//lamda.cpp
#include <iostream>
#include <typeinfo>
#include "lamda.h"
int ext = 10 ;
int main()
{
    // normal
    auto func1 = []()
    {
        cout << "func1:hello world." << endl;
    };
    func1();
    // var func1 type Z4mainE3$_1 ,only auto

    // ignore params
    auto func2 = [] { cout << "func2:haha." << endl; };
    func2();

    // spec ret
    auto func3 = []() -> int { return 1.0; };
    cout << "func3 ret:" << typeid(func3()).name() << "=" << func3() << endl;

    // mutil return spec ret
    auto func4 = [](int i) -> int { if(i>10) return 1; else return 2.3; };
    cout << "func4 ret:" << typeid(func4(5)).name() << "=" << func4(5) << endl;


    funcExt();

    // normal para_list lambda,compared to func9() and func7()
    int a=5,b=6;
    auto func5 = [](int& x,int& y)
    {
        x++,y++;
        return x+y;
    };
    cout << "func5 sum:" << func5(a,b) << " a:" << a << " b:" << b << endl;

    // capture
    // capture opt: -- only capture non-static var
    // blank 不捕获任何变量
    // = 捕获外部作用域所有自动变量，按值传递给函数体，且包含this捕获，如果存在对象
    // & 捕获外部作用域所有自动变量，按引用传递给函数体，且包含this捕获，如果存在对象
    // this 按引用捕获当前对象
    {
        int c=7;
        {
            int e=9;
            {
                int f=11;/*static int ext=10;*/
            }
            auto func6 = [a, c, e, ext/*f*/]()
            {
                // capture f is illegal,not in lambda scope
                // ext is static ,not captured, but capture list allowed -- warning
                cout<<"func6 a:"<<a<<" c:"<<c<<" e:"<<e<<" ext:"<<ext<</*" f:"<<f<<*/endl;
            };
            func6();
        }
        auto func7 = [=,&a]()
        {
            // capture e is illegal,not in lambda scope
            cout<<"func7 a:"<<a<<" c:"<<c<</*" e:"<<e<<*/" ext:"<<ext<<endl;
            a++;
            //c++;
        };
        // var copy ,change not access to c
        func7();
        cout<<"a++: "<<a<<endl;
        cout<<"c++: "<<c<<endl;
        auto func8 = []()
        {
            cout<</*"a:"<<a<<" c:"<<c<<" e:"<<e<<*/"func8 ext:"<<ext<<endl;
            ext =11;
        };
        func8();
        cout<<"access static ext+1: "<<ext<<endl;
        // lambda operator() is const(copy capture) , val capture non-modifiable
        auto func9 = [=]()mutable{ c++;cout<<"c: "<<c<<endl;};
        cout<<"c: "<<c<<endl;
        func9();
        cout<<"func9 c++: "<<c<<endl;
        // capture var copy
    }
    Lamb func;
    func.f();
    // diff between = and &
    auto func11 = [=](){return a;};
    cout<<"a: "<<a;
    a++;
    cout<<" func11 a++: "<<func11()<<endl;
    auto func12 = [&]()
    {
        return b;
    };
    cout<<"b: "<<b;
    b++;
    cout<<" func12 b++: "<<func12()<<endl;
}

 转自：https://blog.csdn.net/qq_31331027/article/details/80878076