glGenTextures causes GL_INVALID_OPERATION

I noticed that glGenTextures isn't generating textures and instead causing GL_INVALID_OPERATION error in the project I'm currently working on, first I thought that there is a missing glEnd or something, I looked for such a thing but everything was OK, so I created this program:

Code:

#include <windows.h>
#include <gl/gl.h>
#include <gl/glu.h>

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, 
    LPSTR lpCmdLine, int nCmdShow) {
	UINT texture = 0;
	glGenTextures(1, &texture);
	GLenum e = glGetError();
	switch (e) {
		case GL_NO_ERROR:
			MessageBox(NULL, "GL_NO_ERROR", "", MB_OK);
			break;
		case GL_INVALID_VALUE:
			MessageBox(NULL, "GL_INVALID_VALUE", "", MB_OK);
			break;
		case GL_INVALID_OPERATION:
			MessageBox(NULL, "GL_INVALID_OPERATION", "", MB_OK);
			break;
	};
	return 0;
}

and it gave the same error
I loaded one of my previous projects and it worked OK.
So what am I doing wrong? does glGenTextures require some initialization (MSDN says nothing about this)?

because you have not setup a rendering context and initialized OpenGL.

well, I guess this is the reason, I was testing a texture class I made to simplify texture operations, and I tried to test it in WinMain, thanks for the response