Bump Mapping

I have a problem trying to do the bump mapping texture, when i want to compile my project, this gave an error that says that the function GlActiveTexture is not define.

I tried to include it in the headers like <GL/gl.h> and <GL/glext.h> but it didn’t work, so in a forum gave me the solution and was to do this validation:

PFNGLACTIVETEXTUREPROC glActiveTexture = (PFNGLACTIVETEXTUREPROC) wglGetProcAddress (“glActiveTexture”);
if(glActiveTexture==NULL){
exit(1);
}
else{
glActiveTexture(GL_TEXTURE0);
}

And oddly works.