OpenGL Contents

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OpenGL Contents

Sid Kraft 46

Interesting, downloaded the files for OpenGL, C++ use in Visual Studio. When I included the headers glut.h, got several compiler errors saying "C" not recognized. Opened the glut.h file and following shown???

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Answer 1

Nancy Vo (WICLOUD CORPORATION) 7,495 Microsoft External Staff Moderator

Hello @Sid Kraft ,

Thanks for your question.

Inside the glut.h file, there is a line of code that says extern "C". This is a special instruction meant only for C++ programs. However, if your main code file in Visual Studio was created with a .c extension instead of a .cpp extension, Visual Studio acts strictly as an older C compiler, gets confused by that command, and throws those errors.

I recommend renaming your source file:

In your Solution Explorer on the right, find your main code file (it might be named Source.c or main.c).
Right-click it, select Rename, and change the extension to .cpp (like main.cpp).

However, I highly recommend we take a step back.

The reason you keep running into these compiler errors, missing .obj files, and Linker issues is because the glut-3.7 files you downloaded are completely obsolete. Modern Visual Studio struggles to read them properly.

As we discussed in the previous thread, the recommended way to avoid all of this manual troubleshooting is to use the modern vcpkg tool that we set up.

Please consider this approach since Visual Studio will automatically link the modern, correct files for you.

Hope this helps. Thank you so much for your patience.

Darran Rowe 2,616 Reputation points

2026-07-07T12:06:55.82+00:00
That is completely incorrect. The Visual C++ Linker has no issues reading these files. While there has been some changes to some specifics, the COFF format and the import library format hasn't changed for 32 bit Windows. As long as you remember that only the Win32 import library was generated, and therefore you only try to build the Win32/x86 platform, then it works.

I believe there were some bad GLUT 3.7 builds going around where the import library was bad, but that was all.

Also, as far as the extern "C" statement goes. Even in the pre-standardised state, the compilers were using the predefined __cplusplus macro to identify themselves. In the GLUT headers, the extern "C" is guarded.

#ifdef __cplusplus extern "C" { #endif

This is true for versions older than GLUT 3.7.

So even building with the compiler in C mode wouldn't result in an error unless __cplusplus was manually defined.
Nancy Vo (WICLOUD CORPORATION) 7,495 Reputation points Microsoft External Staff Moderator

2026-07-08T02:33:17.8133333+00:00

Hi @Darran Rowe ,

Thanks for your answer.

You are correct about the COFF format and the Win32 import library. The underlying issue here is definitely a mismatch between the legacy 32-bit library and a modern 64-bit Visual Studio project configuration, as well as the likelihood that the user downloaded a modified or corrupted version of the 3.7 headers missing the standard __cplusplus guards.

Because the user is a beginner who was hitting multiple linker and compiler roadblocks during manual setup, my primary goal in this thread was to abstract that legacy complexity. Guiding them toward a modern, automated package manager like vcpkg is generally the safest path to get them coding quickly without having to manually reconfigure their build platforms. To be completely transparent, I did not focus deeply on the specific low-level mechanics of GLUT 3.7 simply because the original library has been deprecated and unmaintained.

However, I really appreciate you clarifying the exact low-level mechanics of why those specific legacy files were failing, and I will absolutely take note of this for my own future reference when dealing with legacy setups. Again, thank you for your time.
Nancy Vo (WICLOUD CORPORATION) 7,495 Reputation points Microsoft External Staff Moderator

2026-07-10T02:49:13.4233333+00:00

Hi @Sid Kraft ,

Just checking in to see if you had a chance to review my previous response. Please feel free to reach out if you have any questions - I’m here to help.
Nancy Vo (WICLOUD CORPORATION) 7,495 Reputation points Microsoft External Staff Moderator

2026-07-14T02:46:09.0966667+00:00

Hi @Sid Kraft ,

I haven’t received any recent updates, so I’ll go ahead and close this thread for now. If you have any questions in the future or need further assistance, please feel free to come back and let me know. I’ll be happy to help.

Answer 2

Are you including Windows.h before? On Windows, glut.h includes gl.h and glu.h. These defines functions in a Windows API compatible way, and some of these definitions are only defined in Windows.h.

#include <Windows.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

extern"C"
int wmain()
{
	return 0;
}

This builds without issue on my system.

Screenshot 2026-07-06 193406

Otherwise give the errors exactly as the compiler emits them. Don't try to interpret them. Also, it also helps if you give information as to the file and line that the error occurs on. This way, it lets other people actually inspect the code to determine what is going on.