static main from static class?

Question

I'm trying to figure out why this is not working. I want to do like in Java where main is a static function in a class but this is producing unresolved external symbol error:

 static class MainClass
{
     public:
    static int _tmain(int argc, char* argv[])
    {
        return 0;
    }
};

Why doesn't this work?

Thanks

What are you trying to accomplish by putting `_tmain()` inside a class? — KMån, Sep 18 '10 at 16:48
Why do people have to try to program *"like in language X"*? If in rome, ... — Georg Fritzsche, Sep 18 '10 at 16:49
Tried compiling your code using Code:Blocks on Windows(g++), and I get "error: a storage class can only be specified for objects and functions". Just adding this for the reference of others. Not really providing an answer. — Shamim Hafiz - MSFT, Sep 18 '10 at 16:50
First of all you cannot use static for class declaration. Second, main (or _tmain) is not supposed to be declared as pointer to function. — erjot, Sep 18 '10 at 17:05
I am quite sure that `static class` is not correct Java either... — David Rodríguez - dribeas, Sep 18 '10 at 18:27
`static class` is correct in C++, but it should read `static class OptionalName { ... } NAME;`. He misses the name afterwards. The `static` appertains to the declarator, not the the class. — Johannes Schaub - litb, Sep 18 '10 at 20:27

score 10 · Accepted Answer · answered Sep 18 '10 at 16:48

10

C++ does not work like that.
You need main as a function:

int main(int argc,char* argv[])
{
    //STUFF
}

answered Sep 18 '10 at 16:48

Martin York

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Johannes Schaub - litb · Answer 2 · 2010-09-18T16:54:59.877

Because _tmain is mangled in the binary with the class name MainClass in it, so multiple classes could have a function _tmain in them and not conflict. It's not got the same mangled name as ::_tmain is going to have.

I remember that with an earlier version of MSVC, it accepted the following without a linker error which ended up accidentally as a result of macro expansion in my code base once

namespace bar {
  int main() { }
}

It apparently treated the name main specially and didn't mangle it or mangle it the same as ::main. But such a thing is not Standard conformant. Like in the class case, such a function is completely unrelated to the main function.

score 1 · Answer 3 · answered Sep 18 '10 at 16:53

1

_tmain is called from CRT. You need to set in your linker an entry point to another function that will call MainClass::_tmain instead.

answered Sep 18 '10 at 16:53

ssianky

97
7

score 1 · Answer 4 · edited May 23 '17 at 11:47

1

Because, in C++, you cannot put an entry point inside a class. This answer might help.

edited May 23 '17 at 11:47

Community

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answered Sep 18 '10 at 16:53

KMån

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score 1 · Answer 5 · answered Sep 18 '10 at 20:17

1

Why doesn't that work? Because it's not C++.

struct MainClass {
  static int main(int argc, char** argv) {
    return 0;
  }
};

int main(int argc, char** argv) {
  return MainClass::main(argc, argv);
}

answered Sep 18 '10 at 20:17

score 0 · Answer 6 · answered Sep 18 '10 at 16:50

It's not really C++, so much as the standard linker process which is looking for an export of a specific name (with C-style linkage). The specific export varies based on the compiler and executable type, but the format is specific for each type. For example, Windows GUI exe's have different entry points than console, and specific for ASCII or UNICODE. But the linker is always looking for a function with a specific link name, which is why a static member won't work.

score 0 · Answer 7 · answered Sep 18 '10 at 20:09

You always need main() defined as a global function. This is where the program always starts in C++. You could simple call your static class function from main and pass on the variables if you really want to:

class MainClass
{
     public:
    static int _tmain(int argc, char* argv[])
    {
        return 0;
    }
};

int main(int argc, char* argv[]) {
   return MainClass::_tmain(argc, argv);
}

static main from static class?

7 Answers7