Why does glGetString(GL_VERSION) return null / zero instead of the OpenGL version?

Question

I'm on Linux Mint 13 XFCE. My problem is that when I run in terminal the command:

glxinfo | grep "OpenGL version"

I get the following output:

OpenGL version string: 3.3.0 NVIDIA 295.40

But when I run the glGetString(GL_VERSION) in my application then the result is null. Why doesn't this code get the gl_version?

#include <stdio.h>
#include <GL/glew.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <GL/glext.h>

int main(int argc, char **argv) {

    glutInit(&argc, argv);
    glewInit();

    printf("OpenGL version supported by this platform (%s): \n",
        glGetString(GL_VERSION));
}

Answer 1

glutInit() doesn't create a GL context or make one current. You need a current GL context for glewInit() and glGetString() to work.

Try this:

#include <GL/glew.h>
#include <GL/glut.h>
#include <cstdio>

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutCreateWindow("GLUT");

    glewInit();
    printf("OpenGL version supported by this platform (%s): \n", glGetString(GL_VERSION));
}