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; } 
glGetProgramInfoLog()receives an uninitialise bufferlog. Without testing the functions return code, you attempt to uselogin an error message... there's a funny smell there....printf(strcat(strcpy(msg, "Vertex Shader Failed to Compile!\n> OpenGL Error: "), log));looks like a train wreck. What's wring with something likeprintf("Vertex Shader Failed to Compile!\n> OpenGL Error: %s", log);?