openGL之API学习（一九七）glGetError无限循环返回1282

If you don't have a valid GL context (GL window for example), the GL might simply return GL_INVALID_OPERATION (0x502 = 1282).

void check_error(const char* st)
{
    GLenum err(glGetError());

    while (err != GL_NO_ERROR)
    {
        cerr << "OpenGL error: " << err << " "<<st<<endl;
        err = glGetError();
    }
    cerr << "?\n";
}