How to include <glad/glad.h> into several header files in C++? - c++

Question

I have a project in C++ using opengl. I have main.cpp working with openGL initialization, creating window and stuff like that.
I would like to create a class, where I can outsource loading some texture into Shader.
But when I am trying to use shader.h or glad.h headers as include in any other class-headers, I got error:
fatal error C1189: #error: OpenGL header already included, remove
this include, glad already provides it
If I do all logic inside main.cpp everything is fine, problem raised only if trying to use openGL functions anywhere except main.cpp
main.cpp:
#include <glad/glad.h> // generated from https://glad.dav1d.de
#include "shader.h"
int main()
{
... //Do OpenGL Staff
}
shader.h:
#ifndef SHADER_H
#define SHADER_H
#include <glad/glad.h>
#include <glm/glm.hpp>
class Shader
{
public:
unsigned int ID;
...//some Shader definition staff
}
#endif
and now I want external class "Maze.h" to load it's map inside opengl texture, something like That:
class Maze
{
public:
...//some maze-relate staff
void LoadMazeToGL(Shader* shader)
{
// load and create a texture
// -------------------------
glGenTextures(1, &screenTex1);
glBindTexture(GL_TEXTURE_1D, screenTex1);
// set the texture wrapping parameters
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_REPEAT); // set texture wrapping to GL_REPEAT (default wrapping method)
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_T, GL_REPEAT);
// set texture filtering parameters
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
GLint curMapId = glGetUniformLocation(shader->ID, "shaderInternalVarName");
glUniform1i(curMapId, 2); // Texture unit 2 is for current map.
... //define and fill tex1data using Maze private information
glActiveTexture(GL_TEXTURE0 + 2);
glBindTexture(GL_TEXTURE_1D, screenTex1);
glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA, MazeIntegerSize, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex1data);
}
}

Answer 1

To check for problems like this use the -E flag of GCC/g++ or an alternative for your compiler. This outputs the result of the pre-processor (so the includes etc). You can then have a look at the files produced and look for the double include. You may have just forgotten an include guard somewhere :)