Why is there a macro which defines _tmain?

Question

I am new to C++ coding, coming from Java and C# background. I'm puzzled by the proliferation of #define terms starting with the most basic:

#define _tmain wmain

When I first learned a smattering of C ages ago, the main function was:

int main(int argc, char *argv[])

In the Visual C++ project I created, it made the main function:

int _tmain(int argc, _TCHAR* argv[])

I'm just wondering why there needed to be a name translation from wmain to _tmain? Why not just use the original C main function prototype?

In general there seems to be lot of #define renaming something which looks pretty clear to start with, to something which looks more mysterious and less clear (I mean wmain to _tmain ??).

Thanks for tolerating what may be a very obvious question.

Answer 1

This is a Visual C++-specific feature, it's not a part of C++.

Most of the Windows API functions have two versions: those that end in W, which are for use with wide character strings (wchar_t strings) and those that end in A, which are for use with narrow character strings (char strings). The actual Windows API "functions" don't have any suffix and are defined as macros that expand to the right version depending on the settings.

The T names (like _TCHAR and _tmain) are for the same purpose: they are macros that expand to the right name depending on your compilation settings, so wchar_t and wmain for wide character support, or char and main for narrow character support.

The idea is that if you write your code using the character-type-agnostic names (the T names), you can compile your code to use narrow characters (ASCII) or wide characters (Unicode) without changing it. The tradeoff is that your code is less portable.

Answer 2

Because Microsoft decided that the best way to add Unicode support to C++ was to add a TCHAR type, which is #defined to either char or wchar_t depending on the value of Project Properties > Configuration Properties > General > Character Set. _tmain is also #defined to either main (which takes chars) or wmain (which takes wchar_ts) depending on that setting.