Opengl program sample crash

Question

I compiled the following code:

// Triangle.cpp
// Our first OpenGL program that will just draw a triangle on the screen.

#include <GLTools.h>            // OpenGL toolkit
#include <GLShaderManager.h>    // Shader Manager Class

#ifdef __APPLE__
#include <glut/glut.h>          // OS X version of GLUT
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>            // Windows FreeGlut equivalent
#endif

GLBatch triangleBatch;
GLShaderManager shaderManager;

///////////////////////////////////////////////////////////////////////////////
// Window has changed size, or has just been created. In either case, we need
// to use the window dimensions to set the viewport and the projection matrix.
void ChangeSize(int w, int h)
    {
    glViewport(0, 0, w, h);
    }


///////////////////////////////////////////////////////////////////////////////
// This function does any needed initialization on the rendering context. 
// This is the first opportunity to do any OpenGL related tasks.
void SetupRC()
    {
    // Blue background
    glClearColor(0.0f, 0.0f, 1.0f, 1.0f );

    shaderManager.InitializeStockShaders();

    // Load up a triangle
    GLfloat vVerts[] = { -0.5f, 0.0f, 0.0f, 
                          0.5f, 0.0f, 0.0f,
                          0.0f, 0.5f, 0.0f };

    triangleBatch.Begin(GL_TRIANGLES, 3);
    triangleBatch.CopyVertexData3f(vVerts);
    triangleBatch.End();
    }



///////////////////////////////////////////////////////////////////////////////
// Called to draw scene
void RenderScene(void)
    {
    // Clear the window with current clearing color
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    GLfloat vRed[] = { 1.0f, 0.0f, 0.0f, 1.0f };
    shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);
    triangleBatch.Draw();

    // Perform the buffer swap to display back buffer
    glutSwapBuffers();
    }


///////////////////////////////////////////////////////////////////////////////
// Main entry point for GLUT based programs
int main(int argc, char* argv[])
    {
    gltSetWorkingDirectory(argv[0]);

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_STENCIL);
    glutInitWindowSize(800, 600);
    glutCreateWindow("Triangle");
    glutReshapeFunc(ChangeSize);
    glutDisplayFunc(RenderScene);

    GLenum err = glewInit();
    if (GLEW_OK != err) {
        fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
        return 1;
        }

    SetupRC();

    glutMainLoop();
    return 0;
    }

But when i try to execute it the program crash, then the debugger gives me the following error:

Excepción no controlada en 0x00000000 en Triangle.exe: 0xC0000005: Infracción de acceso al leer la ubicación 0x00000000.

Answer 1

To use glCreateShader(GL_VERTEX_SHADER) you must be running OpenGL 2.0 or higher. One way to tell is to check the value of GLEW_VERSION_2_0 (after your call to glewInit()). If the value is true then OpenGL 2.0 is supported. Otherwise, you may need to update your graphics driver or use a newer graphics card.

Answer 2

The only way that this:

hVertexShader = glCreateShader(GL_VERTEX_SHADER)

Can get a NULL pointer exception (are you sure it's this line and not the one before it?) is if glCreateShader is NULL. GLTools is part of the OpenGL Superbible volume 5's distribution; it's not a "standard" OpenGL tool, so I can't say much about it.

But you seem to be initializing GLEW. And since you don't directly include the GLEW header, I can only guess that GLTools is including it for you. So GLEW's initialization ought to be carrying over to GLTools.

Check the value of "glCreateShader". Follow GLEW's #define for this function all the way back to the actual variable that GLEW defines, and then check this variable's value. If it is NULL, then you've got problems. Perhaps GLEW's initialization failed.