Error of "GL_HISTOGRAM was not declared"

My program came with error of “GL_HISTOGRAM was not declared”, but I did include <gl.h> at its header. Is it correct? Tks.

You need to include <glext.h>, too. The latest version is always available here:

Hi, Stephen A,

Thanks. But, after I added, the same error still existed. Any other recommended? Tks.

For your reference, below is the headers that I used:

#include “gl/math3d.cpp”
#include “gl/glut.h”
#include “gl/torus.c”
#include “gl/vectormath.c”
#include “gl/glext.h”
#include “gl/gltools.cpp”
#include <stdio.h>
#include <stdlib.