C++-lvalue 表示左值

/*
左值
*/ 
#include <iostream>

using namespace std; 

int func(void) {
    int num = 100;     
    return num; //返回值是右值 
}

int main() {
    //int& r = 100; //error 100不能赋予左值 
    const int& r = 100; 
    //int& r4 = func(); //表示进行左值定义 
    const int& r5 = func(); //表示对右值进行赋值 
    cout << r5 << endl;

    int a = 5, b = 2; 
    const int& r6 = a + b; //表示使用右值进行赋值 
    //int& r6 = a + b; //表示进行左值赋值  

    char c = ‘a‘; 
    const int& r3 = c; 
    cout << "&c=" << (void* )&c << endl; 
    cout << "&r3=" << &r3 << endl;
    return 0;  
}

/*
对于a++的左值操作
*/ 
#include <iostream>

using namespace std; 


int main() {
    int a = 1; 
    cout << ++a << endl; 
    cout << a << endl; 
    int& b = a; 
    const int& c = a; 
    cout << c << endl; 

    int& d = ++a; 
    cout << d << endl; 

    (a = 10) = 20; 

    int& e = (a = 10); 
    cout << e << endl; 

}