Compiling with int main(void) fails; main(int argc, char *argv[]) succeeds. Why?

Question

Problem

Why would compiling a program which has an int main(void) main function differ from compiling a program which has an int main(int argc, char *argv[]) main function, if the program does not use arguments passed on the command line?

Is this OS or compiler specific? I do not get the same results using mingw and g++(which is weird isn't it as wingw is a port of gcc).

Example

Code

#include <iostream> #include"SDL/SDL.h" int main(void) { return 0; }

Compilation commands

g++ test.cpp; #g++ 4.4.5 i586-mingw32msvc-g++ test.cpp; # mingw 4.4.4

Error

(Given by the second command.)

a(main.o):(.text+0x85): undefined reference to `_WinMain@16'

It's compiler specific ... but int main (int argc, char *argv[]) is "correct". I would recommend ALWAYS using the latter form in ALL your C and C++ code. — paulsm4
– paulsm4, Commented Dec 29, 2011 at 21:01
Please provide an example program, the exact command you use to invoke the compiler, the exact output of the compiler, and the kind and version of the compiler. Without this information, no one can definitively answer your question. — James McNellis
– James McNellis, Commented Dec 29, 2011 at 21:03
You might consider telling us something a bit more specific than it "fails". Compile error (if so, what's the message?) Linker error (if so, what's the message?) Error at runtime (if so, what?) As it stands, people can just guess. — Ernest Friedman-Hill
– Ernest Friedman-Hill, Commented Dec 29, 2011 at 21:05

jrok · Accepted Answer · 2011-12-29 22:11:25Z

11

This is SDL thing. On Windows, when you include SDL.h,main is redefined to SDL_main which calls WinMain (the real entry point in non-console Windows apps), does some initialization and finally calls your main code. It has a signature with argc and argv and you're pretty much required to follow it, so int main() won't work.

edited Dec 29, 2011 at 22:11

answered Dec 29, 2011 at 21:43

jrok

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5 Comments

danjjl Over a year ago

(I edited incorrectly -> re-edited) Why would it work with g++ then?

jrok Over a year ago

@danjjl Because it's only redefined on Windows. (You're compiling with g++ on some other platform, I assume)

danjjl Over a year ago

Nice :), where did you find the information? is this still true in my example that does not really use SDL?

jrok Over a year ago

It's mentioned in FAQ section on SDL's website and there are numerous threads about this issue in their forums.

danjjl Over a year ago

Right it was because I was not linking SDL (event do I would have thought I did not need to as it was not being used). Linking SDL gives Undefined reference to 'SDL_main' which is covered in the FAQ

Juha Laiho · Accepted Answer · 2011-12-29 21:08:54Z

The specification of main(...) is a contract. In the C language, the contract says that the arguments are int and char **. This is a requirement your program has to fulfill, if it wants the environment to interact with it.

Whether or not your program wants to use the parameters is a different issue -- it just has to abide by the contract that there is a functiona named main, with the correct order and type of parameters.

This question is about C++, not C. That said, this answer is incorrect regardless: int main(void) is a perfectly valid declaration of main in both C (C90, C99, and C11) and C++ (C++98, C++03, and C++11).

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