consider the program:
#include <cstdlib>
#include <iostream>
#include <utility>
using namespace std;
class Test
{
public:
Test(int arg = 0);
Test(const Test &rhs);
Test &operator=(const Test &rhs);
private:
int val;
};
Test::Test(int arg) : val(arg)
{
cout << "Test one arg ctor" << endl;
}
Test::Test(const Test &rhs) : val(rhs.val)
{
cout << "Test copy ctor" << endl;
}
Test &Test::operator=(const Test &rhs)
{
cout << "operator= called" << endl;
if (this != &rhs)
val = rhs.val;
return *this;
}
int main()
{
Test one(1);
cout << endl << "pair ctor" << endl;
pair<int, Test>(1, one);
cout << endl << "make_pair" << endl;
make_pair(2, one);
return EXIT_SUCCESS;
}
I compiled the above program with
g++ -std=c++98 -pedantic -Wall -Wextra x.cpp
The output of the above program is:
Test one arg ctor
pair ctor
Test copy ctor
make_pair
Test copy ctor
Test copy ctor
Here make_pair calls one extra Test copy ctor compared to the
pair<int, Test>(1, one).
Will this be the case always ? If so, can it be concluded that
pair<T1, T2>(const T1 &, const T2 &) should be preferred to
make_pair() ?
Kindly clarify.
Thanks
V.Subramanian
