A strange behavior about constructors in C++

Question

I show you the code directly.

#include <iostream>
#include <stdio.h>

class A {
   public:
   A(const std::string& name){
    std::string aname = "HAHA_" + name;
    std::cout << aname << std::endl;
    }

    ~A(){
         std::cout << "Done." << std::endl;
    }
};

int main() {

   size_t len = 5;
   char szTmp[30] ={0};
   snprintf(szTmp,sizeof(szTmp),"Getlist_V2_%zd",len);
   A a(std::string(szTmp));
   return 0;
}

The expected results are as follows：

HAHA_Getlist_V2_5
Done.

But It outputs nothing at all. When I replace A a(std::string(szTmp)); with A a(szTmp); ,erverything is ok. It confused me for a long time.

Answer 1

A a(std::string(szTmp));

This is a function declaration, believe it or not! So, no A is constructed.

Instead, write this:

A a{std::string(szTmp)};

Or, since an implicit conversion to std::string exists, either of the following will suffice:

A a{szTmp};
A a(szTmp);