I\'ve often seen that people create objects in C++ using
Thing myThing(\"asdf\");
Instead of this:
Thing myThing = Thing(\"
The compiler may well optimize the second form into the first form, but it doesn't have to.
#include
class A
{
public:
A() { std::cerr << "Empty constructor" << std::endl; }
A(const A&) { std::cerr << "Copy constructor" << std::endl; }
A(const char* str) { std::cerr << "char constructor: " << str << std::endl; }
~A() { std::cerr << "destructor" << std::endl; }
};
void direct()
{
std::cerr << std::endl << "TEST: " << __FUNCTION__ << std::endl;
A a(__FUNCTION__);
static_cast(a); // avoid warnings about unused variables
}
void assignment()
{
std::cerr << std::endl << "TEST: " << __FUNCTION__ << std::endl;
A a = A(__FUNCTION__);
static_cast(a); // avoid warnings about unused variables
}
void prove_copy_constructor_is_called()
{
std::cerr << std::endl << "TEST: " << __FUNCTION__ << std::endl;
A a(__FUNCTION__);
A b = a;
static_cast(b); // avoid warnings about unused variables
}
int main()
{
direct();
assignment();
prove_copy_constructor_is_called();
return 0;
}
Output from gcc 4.4:
TEST: direct
char constructor: direct
destructor
TEST: assignment
char constructor: assignment
destructor
TEST: prove_copy_constructor_is_called
char constructor: prove_copy_constructor_is_called
Copy constructor
destructor
destructor