title: Linker error : undefined reference to symbol 'glOrtho'
body: <p>I installed OpenGL packages in Ubuntu 13.04 ( <code>*mesa-common-dev freeglut3-dev*</code> ) and tried to run a sample program. </p>
  
  <pre><code>#include "GL/freeglut.h"
  #include "GL/gl.h"
  
  /* display function - code from:
       http://fly.cc.fer.hr/~unreal/theredbook/chapter01.html
  This is the actual usage of the OpenGL library. 
  The following code is the same for any platform */
  void renderFunction()
  {
      glClearColor(0.0, 0.0, 0.0, 0.0);
      glClear(GL_COLOR_BUFFER_BIT);
      glColor3f(1.0, 1.0, 1.0);
      glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
      glBegin(GL_POLYGON);
          glVertex2f(-0.5, -0.5);
          glVertex2f(-0.5, 0.5);
          glVertex2f(0.5, 0.5);
          glVertex2f(0.5, -0.5);
      glEnd();
      glFlush();
  }
  
  /* Main method - main entry point of application
  the freeglut library does the window creation work for us, 
  regardless of the platform. */
  int main(int argc, char** argv)
  {
      glutInit(&amp;argc, argv);
      glutInitDisplayMode(GLUT_SINGLE);
      glutInitWindowSize(500,500);
      glutInitWindowPosition(100,100);
      glutCreateWindow("OpenGL - First window demo");
      glutDisplayFunc(renderFunction);
      glutMainLoop();    
      return 0;
  }
  </code></pre>
  
  <p>However, I encountered this error and don't know what to make of it.</p>
  
  <pre><code>ved@vedvals:~/Desktop/p1$ g++ p1.cpp -lglut
  /usr/bin/ld: /tmp/ccgGdeR2.o: undefined reference to symbol 'glOrtho'
  /usr/bin/ld: note: 'glOrtho' is defined in DSO /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1 so try adding it to the linker command line
  /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1: could not read symbols: Invalid operation
  collect2: error: ld returned 1 exit status
  </code></pre>
  
  <p>I had a look at<br>
  <a href="https://stackoverflow.com/questions/11475817/opengl-hello-c-fails-to-build-using-cmake">OpenGL hello.c fails to build using CMake</a><br>
  as the error is similar but I am not using CMake</p>
  
  <p>IS my code wrong or do I need to include/change/tweak some settings?</p>
  
  <p>I referred this site for installation and code :</p>
  
  <p><a href="http://www.codeproject.com/Articles/182109/Setting-up-an-OpenGL-development-environment-in-Ub" rel="nofollow noreferrer">Setting up an OpenGL development environment in Ubuntu Linux</a></p>