Proper library inclusion - problem

**cyb3rman** · 07-28-2014

Hello guys!

I have these 3 files:

Code:

//main.cpp

#include "lib.h"


int main ()
{
    foo();
    return 0;
}

Code:

//lib.h

void foo();

Code:

//lib.cpp

#include "lib.h"
#include <iostream>


void foo()
{
    std::cout<<"it works!";
}

and in Dev-C++ I get an error that says: "undefined reference to foo".
I know it's very simple, am I missing something in the code? Should I compile/link them manually from console?

Note: I read that this is the recommended way to write/include a libray, but I still don't understand how lib.cpp gets to be used in main.cpp as main.cpp only has a reference of lib.h, and lib.h doesn't say anything about the source file (lib.c).

Thanks!

**Elysia** · 07-28-2014

You need to compile both main.cpp and lib.cpp. The linker takes the output from the compiler of both these and puts them together into one file.

**cyb3rman** · 07-28-2014

I can't compile lib.cpp because I get this error: "c:\crossdev\src\mingw-w64-svn\mingw-w64-crt\crt\crt0_c.c undefined reference to `WinMain'"

**Elysia** · 07-28-2014

g++ main.cpp lib.cpp -o myapp.exe
Do not compile separately.
If you are compiling from your IDE, ensure you are writing a console app, not a windows app.

**cyb3rman** · 07-28-2014

Thanks, somehow I managed to use the cl command instead of g++, but only in an (elevated) window that had previously run "vcvarsall.bat x86". Any other one gives me the error that says "cl is not recognized as an int/ext command".

Still, some things are not clear to me:why have I got all these errors in Dev?

**Elysia** · 07-28-2014

I am not familiar with Dev-C++, but perhaps you did not add all your source files to your project.
cl is also the executable name for Microsoft's C++ compiler, shipped with the Visual Studio IDE.

**cyb3rman** · 07-29-2014

Thanks a lot!

Apparently, I should have created a project in which all files should have been added

I knew it was too simple to be a code problem

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