glCreateShader is crashing
Solution 1
You have to initialize GLEW before you can use it:
GLenum err = glewInit();
Solution 2
There is another situation when this can happen and the conditions are far from obvious. If you decide to use glfw AND glew in your application, you can also end in glCreateShader() ACCESS_VIOLATION, if you wrote:
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
If you change this line to
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);
the ACCESS_VIOLATION due to the NULL function pointer glCreateShader() is gone.
Do not ask me, how the two libraries glew and glfw interfere with each other... voodoo alert!
Solution 3
Here is my variant which is a follow up from @BenRujil's answer above.
glewExperimental = GL_TRUE;
if(glewInit() != GLEW_OK)
throw std::runtime_error("glewInit failed");
Solution 4
If you're using GLFW and GLEW/GLXW, getting an access violation for address 0 can happen if you're trying to initialize GLEW/GLXW before creating a valid openGL context with GLFW:
if (!glfwInit()) {
std::cerr << "GL initialization failed" << std::endl;
return 1;
}
// Setup the openGL profile you need - we're going with a 4.3 core profile
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
// Context creation happens in the line below
GLFWwindow *window = glfwCreateWindow(800, 600, "text", NULL, NULL);
if (!window) {
std::cerr << "Window or GL initialization failed";
glfwTerminate();
return 1;
}
glfwMakeContextCurrent(window);
if (glxwInit()) { // Now it's a good time to initialize Xtension wranglers
std::cerr << "Failed to initialize GLXW" << std::endl;
return 1;
}
Calling glxwInit()
before context creation will pick up whatever default context is set and can trigger the access violation (might need to be picked up at runtime).
Solution 5
If it's a problem with GLFW, you can ask them for an error message before they crash your program.
Windows example:
Create a callback function:
#include <windows.h>
void glfw_onError(int error, const char* description)
{
// print message in Windows popup dialog box
MessageBox(NULL, description, "GLFW error", MB_OK);
}
and set it at the very beginning of your code.
glfwSetErrorCallback(glfw_onError);
I did that and got "The GLFW library is not initialized.
" Turns out my GLFW library wasn't initialized. Turns out Ben's answer was right. I just had glfwInit()
in an assert like this: assert(glfwInit());
so it was being stripped when I compiled my program for Release.
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Parker Olson
Updated on November 26, 2020Comments
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Parker Olson over 3 years
I should have the newest version of Glew and Glut so that shouldn't be the problem. Everything should be linked, and I'm using MS visual studio 2010. My program compiles but when I get to glCreateShader(GL_FRAGMENT_SHADER) it show an error: "0xC0000005: Access violation."
my program:
#include <GL\glew.h> #include <GL\glut.h> #include <stdio.h> #include <stdlib.h> GLuint program; static char* readShaderSource(const char * shaderFile) { FILE* fp = fopen(shaderFile, "r"); char* buf; long size; if (fp == NULL) return NULL; fseek(fp, 0L, SEEK_END);//go to end size = ftell(fp); //get size fseek(fp, 0L, SEEK_SET);//go to begining buf = (char*) malloc((size +1) * sizeof(char)); fread(buf, 1, size, fp); buf[size] = NULL; fclose(fp); return buf; } static void initShader(const GLchar * fsFile) { GLint status; GLchar * fSource; GLuint fShader; GLuint fShader2; //read file fSource = readShaderSource(fsFile); if (fSource == NULL) { printf("Fail to load file"); exit(EXIT_FAILURE); } //Create program and shader object fShader2 = glCreateShader(GL_VERTEX_SHADER); fShader = glCreateShader(GL_FRAGMENT_SHADER); program = glCreateProgram(); //Attach shaders to program glAttachShader(program, fShader); //read shaders glShaderSource(fShader, 1, (const GLchar**) &fSource, NULL); //compile fragment shader glCompileShader(fShader); //error check glGetShaderiv(fShader, GL_COMPILE_STATUS, &status); if (status == GL_FALSE) { printf("Failed to compile the fragment shader."); exit(EXIT_FAILURE); } //link and error check glLinkProgram(program); glGetProgramiv(program, GL_LINK_STATUS, &status); if (status == GL_FALSE) { printf("program error"); exit(EXIT_FAILURE); } //use program object glUseProgram(program); //set up uniform parameter //skipped for now } int main(int argc, char ** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(500,500); glutCreateWindow("Matrix Fractal"); glClearColor(1.0, 1.0, 1.0, 1.0); gluOrtho2D(0.0,0.0,(GLfloat) 500, (GLfloat) 500); glutDisplayFunc(draw); glutReshapeFunc(reshape); initShader("fsFractal.glsl"); glutMainLoop(); }
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sinner over 9 yearsThanks Ben. It worked. However I used another variant which I am posting as an answer below for clarity sake.
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jimvonmoon over 9 yearsI solved that problem by calling glewInit() after glfwMakeContextCurrent().
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scones over 8 yearsIn addition to @jimvonmoon 's suggestion, the window to which the shader belongs, has to be current at that time of the shader creation. This was my mistake.
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Matth over 6 yearsThanks, you saved me from 10 days of debugging