multiple main functions in c language

In addition to the other comments, it is possible at link time to specify the program's entry point[^], but you need to understand the potential for problems.

The only language in which I've used "multiple main" functions is Java. There you can put a public static void main(String[] args) into an class and you can start the main() function of any class from the IDE (for example Eclipse). This can be useful to put in small test cases into the classes. Still, when you finally package your product you have to mark one of these classes as the main class (like com.mycompany.MainClass) in your manifest file and when someone starts your program (for example from a jar file) then only one main is valid.

In C you don't even have namespaces (like packages and classes in java) so you simply can't implement features like this. If you want test functions in several places (like in java) then you can do that this way:
Something.c:

... blah blah normal release code of Something.c ...


#if BUILD_DEBUG
void MyTestCode_2()
{
    ... blah blah blah ...
}
#endif

main.c:

int main(int argc, char* argv[])
{
#if BUILD_DEBUG
    // this stupid if helps avoiding "unreachable code" warnings in most compilers
    // and helps you to turn on/off debug test code
    if (1)
    {
        // you can declare and call any of your test functions here
        void MyTestCode_2();
        MyTestCode_2();
        return 0;
    }
#endif

    ... original main code ...
}

In addition to Solution 1:

Your problem is the way you approach asking questions. Certainly, the whole idea to use multiple entry points is based on some misconception, quite a big on. But what is it? We don't know. Therefore, it's always a good idea to share your thinking and explain your ultimate goals. It would give us a chance to really help you, by explaining the misconception and suggestion a really working alternative.

[EDIT]

For example, if you meant to have this application started in different environments or by different applications, the answers would be "it's wrong to start a separate process without a good reason, instead, make your module a DLL (shared library), not application".

If you means to run this application in different ways, depending on how the user specifies it, the answer would be "use the command line".

And so on…

—SA

You can have 2 or more main() functions in your source code anyway. Even so, only one of them will be compiled. One practical case is if you're going cross-platform.

//sample.c
#define WIN32

#ifdef WIN32
int main()
{
  //in this case only this main() will be compiled.
}
#endif

#ifdef LINUX
int main()
{
  //another main for linux platform
}
#endif

#ifdef UNIX
int main()
{
  //another main for unix platform
}
#endif

In the above application there're 3 main() functions defined. But only the main() at the top will be compiled.

Your application's source code can contain more than one main() function and one of them must be chosen before compiling with the help of the pre-processor.

Your question is same as asking can I have multiple functions of the same name in a C program? The answer is no, as the compiler will not which one to choose when the name is encountered. Similarly to questions like "multiple declaration of variables of the same name" etc. It should be detected as errors by the compiler. Hope it helps :-).