calling glGetString ( GL_VERSION ) on mac OS X tiger in c xcode project

I can't figure out what include I need to put in to access glGetString

#include <stdio.h>
#include <OpenGL/gl.h>
#include <OpenGL/OpenGL.h>

int main (int argc, const char * argv[]) {
const GLubyte * strVersion = glGetString ( GL_VERSION );
printf("Hello, World!\n");
printf(strVersion);
return 0;
}

runs with a message
unknown symbol '_glGetString'

.

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