Left value, right value

1. Basic concepts

（1）
The left value ： You can take its address

Right value ： You can't take its address

int main()
{
    
    //int& a=10;// error ： An lvalue reference cannot reference a constant , Lvalue reference is equivalent to ：int* const( Constant pointer ),
    const int& a=10;// correct 
    /*  Equivalent to ： int tmp=10; const int* const a=&tmp; */
}

（2）

int fun()
{
    
    int a=10;
    return a;
}
int main()
{
    
    int x=fun();
    
    //int& b=fun(); error 
    const int& c=fun();// correct 
    
    int&& d=fun();
    
    return 0;
}

The analysis of the above code is as follows ：

2. lvalue reference 、 Right quoting

（1）

lvalue reference ： You need to reference a variable with a name , You cannot reference an unnamed object .

Right quoting ： Only literal constants can be referenced , No name .

Because will die value is an unnamed object , So you can't use lvalue to reference , Can only be referenced with an R-value , And through the right value reference , It also increases the life cycle of the dying value .

3. Mobile build ：

The heap memory is built once , If there is no mobile build , It will be built three times

notes ： If there is a moving object, first mobilize the moving structure to frame the dead value object , Instead of calling ordinary copy constructs , If you don't move the structure , The normal copy construct will be called to construct the dead value object .