Don't quite understand why this copy constructor is not invoked when I build with debug mode using VC2010.
SomeClass(const SomeClass& sc)
cout << "Copy Constructor invoked!" << endl;
SomeClass test(SomeClass(9999)); // Copy constructor not invoked.
It is an optimization done by the compiler. According to the language specification, the compiler is allowed to omit the call to the copy-constructor whenever it can.
An accessible copy-constructor is needed for semantic check only, even though it is not actually called. Semantic check is done much before the optimization.
However, if you compile it with
-fno-elide-constructors option with GCC, then the copy-elision will not be performed, and the copy-constructor will be called. The GCC doc says,
The C++ standard allows an implementation to omit creating a temporary which is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases.
With MSVC10, you can use /Od which according to the MSDN turns off all optimizations in the program.
Note : Wikipedia has an article on copy elision