glGetProgramIv() doesn't change the pointer sent to it - c++

Question

I have this function:
void GetAllUniforms(unsigned int prog) {
int total = -1;
glGetProgramiv(prog, GL_LINK_STATUS, &total);
printf("total & prog: %d %d\n", total, prog);
for(int i=0; i<total; ++i) {
int name_len=-1, num=-1;
GLenum type = GL_ZERO;
char name[100];
glGetActiveUniform(prog, i, sizeof(name)-1,
&name_len, &num, &type, name);
name[name_len] = 0;
unsigned int location = glGetUniformLocation(prog, name);
printf("Name: %s/Number: %d/Location: %d\n", name, num, location);
}
}
It's purpose is simple, get all uniforms and print them,
however, let's say I ran this function, right?
It would give me:
Running newpmo/build/out
total & prog: -1 1
It's clear, there are no active uniforms in my glsl shaders, which is ridiculous cause I have a WorldMatrix multiplying a Position Vector to get Gl_Position, and upon further debugging I found that if I set total to another number, let's say 5, I get this:
Running newpmo/build/out
total & prog: 5 1
Name: /Number: -1/Location: -1
Name: /Number: -1/Location: -1
Name: /Number: -1/Location: -1
Name: /Number: -1/Location: -1
Name: /Number: -1/Location: -1
This is pretty odd, cause it shows that glGetProgramiv is not actually affecting total in any way, even though I sent it my address and the program is compiled and linked properly!
How is that possible?

Answer 1

GL_LINK_STATUS returns whether the program has been successfully linked or not. So even if that line had worked correctly, the result is not a value you should be looping over. Given what you're trying to do, the value you want to query is GL_ACTIVE_UNIFORMS.
However, on to your principle problem. You are getting some kind of OpenGL error from this (BTW: always check for OpenGL errors). I know that because the only reason that function would not set the variable is if it errors out. So go fetch the error.
Since it's not an obvious error (like passing the wrong enum or something), what's probably happening is not something that's visible from here. That is, you're not passing a valid program to this function. You could be passing a shader object instead of a program object, or you could be passing a value you didn't get from glCreateProgram.