Unhandled exception in C++ for Opengl [closed] - c++

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I've been working on an OpenGL tutorial for a few days. I got the first Tutorial to work but once I got to the second tutorial it throws
First-chance exception at 0x00000000 in playground.exe: 0xC0000005: Access violation.
Unhandled exception at 0x00000000 in playground.exe: 0xC0000005: Access violation.
My code is
#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <glfw3.h>
GLFWwindow* window;
#include <glm/glm.hpp>
using namespace glm;
int main( void )
{
// Initialise GLFW
if( !glfwInit() )
{
fprintf( stderr, "Failed to initialize GLFW\n" );
return -1;
}
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
glfwWindowHint(GLFW_SAMPLES, 4);
glfwWindowHint(GLFW_RESIZABLE,GL_FALSE);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
// Open a window and create its OpenGL context
window = glfwCreateWindow( 1024, 768, "Playground", NULL, NULL);
if( window == NULL ){
fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
// Initialize GLEW
if (glewInit() != GLEW_OK) {
fprintf(stderr, "Failed to initialize GLEW\n");
return -1;
}
// Ensure we can capture the escape key being pressed below
glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
// Dark blue background
glClearColor(0.0f, 0.0f, 0.4f, 0.0f);
// An array of 3 vectors which represents 3 vertices
static const GLfloat g_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f,
};
// This will identify our vertex buffer
GLuint vertexbuffer;
// Generate 1 buffer, put the resulting identifier in vertexbuffer
glGenBuffers(1, &vertexbuffer);
// The following commands will talk about our 'vertexbuffer' buffer
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
// Give our vertices to OpenGL.
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
do{
// Draw nothing, see you in tutorial 2 !
// 1rst attribute buffer : vertices
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(
0, // attribute 0. No particular reason for 0, but must match the layout in the shader.
3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
// Draw the triangle !
glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
glDisableVertexAttribArray(0);
// Swap buffers
glfwSwapBuffers(window);
glfwPollEvents();
} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
glfwWindowShouldClose(window) == 0 );
// Close OpenGL window and terminate GLFW
glfwTerminate();
return 0;
}

Answer 1

Wrong command sequencing. You have this:
int main( void )
{
...
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
...
window = glfwCreateWindow( 1024, 768, "Playground", NULL, NULL);
...
glfwMakeContextCurrent(window);
...
if (glewInit() != GLEW_OK) {
...
}
Since you're using GLEW function pointers like glGenVertexArrays() and glBindVertexArray() aren't valid until a successful glewInit().
Move your VAO creation to after glewInit():
int main( void )
{
...
window = glfwCreateWindow( 1024, 768, "Playground", NULL, NULL);
...
glfwMakeContextCurrent(window);
...
if (glewInit() != GLEW_OK) {
...
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
...
}
Since you're creating a GL 2.1 context you should explicitly check for ARB_vertex_array_object support before you use VAOs. VAOs weren't core until GL 3.0.
Your use of generic vertex attributes without corresponding shaders is iffy at best. Supply some shaders or drop back to glVertexPointer() and friends.