What is the difference between _tmain() and main() in C++?

In C++, the main() function is the most common entry point for programs, while _tmain() is a Microsoft Visual C++-specific entry point function designed to support both Unicode and ANSI character encodings.

main() Function

The main() function serves as the entry point for standard C++ programs. It comes in two forms:

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

Here, argc represents the number of command-line arguments, and argv is an array of character pointers used to store the arguments.

_tmain() Function

_tmain() is an extension in Microsoft Visual C++ that simplifies handling Unicode and ANSI character encodings. Its implementation relies on the definitions of the macros _UNICODE and _MBCS:

• If _UNICODE is defined, _tmain() maps to wmain(), which has the prototype int wmain(int argc, wchar_t* argv[]).
• If _MBCS is defined or neither macro is defined, _tmain() maps to main().

This mapping enables developers to write encoding-independent code, allowing reuse of the code across different encoding settings without modifying the function entry point.

Example

Suppose you need to write a program that processes command-line arguments and supports both Unicode and ANSI encoding seamlessly. Using _tmain() achieves this, for example:

cpp
#include <tchar.h>
#include <iostream>

int _tmain(int argc, _TCHAR* argv[]) {
    std::wcout << L"Number of arguments: " << argc << std::endl;
    for(int i = 0; i < argc; ++i) {
        std::wcout << L"Argument " << i << L": " << argv[i] << std::endl;
    }
    return 0;
}

In this example, the program properly processes command-line arguments in both Unicode and ANSI encodings through the _tmain() function.

In summary, _tmain() is primarily used in the Microsoft Visual C++ environment to provide native Unicode support, while main() is the standard entry function for all C++ environments. For cross-platform C++ programs, main() is typically used; for programs that leverage Windows-specific features, _tmain() can be considered.