C ++中构造函数和析构函数的执行顺序

Question

i have c++ little code, with constructors and destructors.

#include <iostream> 
using namespace std; 
class K { 
public: 
    K(){cout<< "3 ";} 
    ~K(){cout<< "1 ";} 
}; 
int main() 
{ 
    { 
        K a; 
        { 
            K b; 
        } 
        { 
            K c; 
        } 
    } 
    system("pause"); 
    return 0; 
}

problem: i don't understand why answer is: 331311

and not: 333111 .

i know that first running constructors and last destructors but inverted.

Answer 1

Your code will be a lot easier to understand if it is aligned properly:

int main() 
{ 
    { 
        K a;  // a is being constructed
        { 
            K b; // b is being constructed
        } // b is being destructed
        { 
            K c; // c is being constructed
        } // c is being destructed
    } // a is being destructed

    system("pause");
    return 0; 
}

The general rule is, that a locally (automatically) allocated variable lives only inside its scope.

{
    SomeType a; // Creation
} // all local variables from matching { are destroyed