#include <iostream>
struct A
{
A() { std::cout << "Def Constr\n"; }
A(const A&) { std::cout << "Copy Constr\n"; }
};
A func1()
{
return A{};
}
void func2(A a) {}
int main()
{
func2(func1());
}
After compiling with
g++ Copy.cpp -std=c++11 -fno-elide-constructors
Output is :
Def Constr
Copy Constr
Copy Constr
And my questions is : Why 2 Copy Constr ? I thought only 1 Copy was needed.
I might have a guess that func1() throws a temp object and this temp object needs to be copied to another memory region and from that region again a copy must be made for the func2() parameter but it's vague for me .
Could you explain it in detail please ?
func1
is copied from the expression A{}
. func1()
is copied into the function parameter of func2
. Yes your understanding is right. Your line of code (without copy eliding) is similar to
int main()
{
{
A temp = func1(); // 2nd copy
func2(temp); // 3rd copy
}
}
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