Thread: Declaring Class function error?

Hi all,

I am experiencing a strange problem when declaring classes outside the main source file in VC++. I have made an experiment that demonstrates my problem. There are two files: “main.cpp” and “class.cpp”.

“main.cpp” content:

Code:

#include "class.cpp"

int main() {
	return 0;
}

“class.cpp” content:

Code:

class Class {
public:
	void Test();
};

void Class::Test() {
	return;
}

When I try to compile I get following error:

--------------------Configuration: main - Win32 Debug--------------------
Compiling...
main.cpp
class.cpp
Linking...
class.obj : error LNK2005: "public: void __thiscall Class::Test(void)" (?Test@Class@@QAEXXZ) already defined in main.obj
Debug/main.exe : fatal error LNK1169: one or more multiply defined symbols found
Error executing link.exe.

main.exe - 2 error(s), 0 warning(s)

It says that the function void Test() is already declared, but how? Please help me, am I doing something wrong?

Use inclusion guards around your class declaration too.

Code:

#ifndef MY_CLASS_H
#define MY_CLASS_H

class my_class { ...  };

#endif

Hey thanks that helpt (renaming to class.h), thanks

Thanks for the tip, Zach. I will keep that in mind

You'll also need constructors because you don't have any.

Then changing the file class.h doesn't really change any thing hell it could be a .c file and you r code wouldn't work

In the absence of any explicitly defined constructors, the compiler will provide a do-nothing default constructor (which takes no arguments), and a copy constructor (which makes a shallow copy of your class).

Also, there is one exception to what Shiro said. Templated classes often have to be defined in the same file they are declared (usually a header file). The reason is that many compilers (not all, but many) will choke if they are in separate files.