OpenGL: Buffer Objects/Shaders going out of scope - c++

Question

I'm learning OpenGL and I have a problem.
I know that all the memory is allocated onto the GPU by OpenGL, so technically scope shouldn't be an issue? However, when I try to do this:
int SetUpVertexShader(){
glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
//BUILD AND COMPILE SHADER
//VERTEX SHADER
GLuint vertexShader;
vertexShader = glCreateShader(GL_VERTEX_SHADER);
//snip - code to compile shader, etc etc
}
};
int SetUpFragmentShaderandLink(){
//BUILD AND COMPILE SHADER
//FRAGMENT SHADER
GLint success;
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
//snip - code to compile shader, etc etc
};
int linkShaders(){
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader); //this line has complaints saying vertexShader is an undeclared identifier
glAttachShader(shaderProgram, fragmentShader); // this line also has complaints saying fragmentShader is an undeclared identifier
//the rest of the lines all have undeclared identifier complaints
glLinkProgram(shaderProgram);
//check linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if(!success){
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED" << infoLog << std::endl;
}
};
then once I get to the linking shaders and program function linkShaders, I get complaints saying that the vertex shader and fragment shader are out of scope (more specifically, I get told that those two are "undeclared identifiers"). If these are being allocated on the GPU, instead of on the stack, then why am I being told they are going out of scope? Am I doing something wrong?

Answer 1

Your variables need to be in scope to use them (this is true regardless of OpenGL involved or not).
What glCreateShader and glCreateProgram return and glAttachShader and glLinkProgram use are handles (unique identifiers for specific purposes) to OpenGL objects. Make sure to save them in a place where you can access them when you need to supply them to other OpenGL calls (especially to cleanup functions if you no longer need the resources you initially requested).

Answer 2

The issue is not the memory itself being out of scope, as GPU memory is following a Heap-Pattern, while variables goong out of scope can only happen in a Stack-Pattern.
The issue is that the Pointer to this memory, which is stored in CPU Memory, is located on the stack and going out of scope. So you simply have to declare your GLuint Pointers outside the function body.