OpenGL Shader Compilation and Linking Error

Question

I have a method that creates and returns a shader program from two given strings (vertex and fragment shader filenames). Initially, it was working perfectly, with the compilation and linking being successful, before randomly failing and giving me an error message of unicode emoji's.

Example Code:

#define GLEW_STATIC
#define NO_SDL_GLEXT
#include <GL/glew.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFSIZE 1024
#define MAXSIZE 1048576

typedef struct Shader {
  unsigned int data;
} Shader;

char* loadshader(char*);
Shader* createShader(char* vertexfile, char* fragmentfile) {
  const char* vertexcode = loadshader(vertexfile);
  unsigned int vertex = glCreateShader(GL_VERTEX_SHADER);
  glShaderSource(vertex, 1, &vertexcode, NULL);
  glCompileShader(vertex);

  {
    char log[512]; int success; glGetProgramiv(vertex, GL_COMPILE_STATUS, &success);
    printf("Vertex File Name: %s\n", vertexfile); printf("Vertex Code: %d\n", vertexcode); printf("Vertex Value: %d\n", vertex);
    glGetProgramInfoLog(vertex, 512, NULL, log);
    printf("Vertex Shader Failed to Compile!\n> OpenGL Error: %s\n\n - - - - - \n\n", log);
  }

  const char* fragmentcode = loadshader(fragmentfile);
  unsigned int fragment = glCreateShader(GL_FRAGMENT_SHADER);
  glShaderSource(fragment, 1, &fragmentcode, NULL);
  glCompileShader(fragment);

  {
    char log[512]; int success; glGetProgramiv(fragment, GL_COMPILE_STATUS, &success);
    printf("Fragment File Name: %s\n", fragmentfile); printf("Fragment Code: %d\n", fragmentcode); printf("Fragment Value: %d\n", fragment);
    glGetProgramInfoLog(fragment, 512, NULL, log);
    printf("Fragment Shader Failed to Compile!\n> OpenGL Error: %s\n\n - - - - - \n\n", log);
  }

  unsigned int data = glCreateProgram();
  glAttachShader(data, vertex);
  glAttachShader(data, fragment);
  glLinkProgram(data);

  {
    char log[512]; int success; glGetProgramiv(data, GL_LINK_STATUS, &success);
    printf("Program Value: %d\n", data); glGetProgramInfoLog(data, 512, NULL, log);
    printf("Shader Failed to Link!\n> OpenGL Error: %s", log);
  }

  glDeleteShader(vertex);
  glDeleteShader(fragment);
  free((void*) vertexcode);
  free((void*) fragmentcode);

  Shader* shader = (Shader*) malloc(sizeof(Shader));
  shader -> data = data;
  return shader;
}

int WinMain(int argc, char const *argv[]) {
  SDL_Init(SDL_INIT_VIDEO);
  SDL_Window* window = SDL_CreateWindow("Basic Window", 660, 240, 600, 600, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
  SDL_GLContext context = SDL_GL_CreateContext(window);
  glewInit();
  Shader* shader = createShader("data/test.vs", "data/test.fs");
  return 0;
}

char* loadshader(char* filename) {
  FILE* file = fopen(filename, "r");
  if (!file)
    return NULL;

  int flag = 0;
  char* shader = (char*) malloc(MAXSIZE);
  char* buffer = (char*) malloc(BUFFSIZE);
  while (fgets(buffer, BUFFSIZE, file) != NULL)
    strcat(shader, buffer);

  free(buffer);
  fclose(file);

  printf("\"%s\" Content:\n%s\n", filename, shader);
  return shader;
}

The output of the print statements are as follows:

"data/test.vs" Content:
#version 330 core
layout (location = 0) in vec3 POSITION;

void main() {
  gl_Position = vec4(POSITION, 1.0);
}

Vertex File Name: data/test.vs
Vertex Code: -1521078208
Vertex Value: 1
Vertex Shader Failed to Compile!
> OpenGL Error: ░╗x¥j☻

 - - - - -

"data/test.fs" Content:
#version 330 core
out vec4 COLOR;

void main() {
  COLOR = vec4((1.0f, 0.5f, 0.2f, 1.0f);
}

Fragment File Name: data/test.fs
Fragment Code: -1486147520
Fragment Value: 2
Fragment Shader Failed to Compile!
> OpenGL Error: ░╗x¥j☻

 - - - - -

Program Value: 3
Shader Failed to Link!
> OpenGL Error: Fragment shader(s) were not successfully compiled before glLinkProgram() was called.  Link failed.

Solution: The error was in my GLSL shader code, not the code I was using to compile the shaders. That being said, I also made changes to properly check for compilation and linking errors based on @Rabbid76 and @David Sullivan's responses.

Shader* createShader(char* vertexfile, char* fragmentfile) {
  const char* vertexcode = loadshader(vertexfile);
  unsigned int vertex = glCreateShader(GL_VERTEX_SHADER);
  glShaderSource(vertex, 1, &vertexcode, NULL);
  glCompileShader(vertex);

  {
    char log[1024]; int success; glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);
    if (!success) {
      glGetShaderInfoLog(vertex, 1024, NULL, log);
      printf("Vertex Shader Failed to Compile!\n> OpenGL Error: %s\n", log);
    }
  }

  const char* fragmentcode = loadshader(fragmentfile);
  unsigned int fragment = glCreateShader(GL_FRAGMENT_SHADER);
  glShaderSource(fragment, 1, &fragmentcode, NULL);
  glCompileShader(fragment);

  {
    char log[1024]; int success; glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);
    if (!success) {
      glGetShaderInfoLog(fragment, 1024, NULL, log);
      printf("Fragment Shader Failed to Compile!\n> OpenGL Error: %s\n", log);
    }
  }

  unsigned int data = glCreateProgram();
  glAttachShader(data, vertex);
  glAttachShader(data, fragment);
  glLinkProgram(data);

  {
    char log[1024]; int success; glGetProgramiv(data, GL_LINK_STATUS, &success);
    if (!success) {
      glGetProgramInfoLog(data, 1024, NULL, log);
      printf("Shader Failed to Link!\n> OpenGL Error: %s", log);
    }
  }

  glDeleteShader(vertex);
  glDeleteShader(fragment);
  free((void*) vertexcode);
  free((void*) fragmentcode);

  Shader* shader = (Shader*) malloc(sizeof(Shader));
  shader -> data = data;
  return shader;
}

Answer 1

If the compiling of a shader succeeded has to be checked by glGetShaderiv and the parameter GL_COMPILE_STATUS instead of glGetProgramiv. THe log can be get with glGetShaderInfoLog instead of glGetProgramInfoLog e.g.:

glCompileShader(vertex);

{
    glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);
    if (!success) {
        // [...]

        glGetShaderInfoLog(vertex, 512, NULL, log);
        printf(strcat(strcpy(msg, "Vertex Shader Failed to Compile!\n> OpenGL Error: "), log));
    }
}