Question

Is it possible to pass an enum as a parameter to a variadic function? I’m trying to do the following:

GLenum ShaderManager::initialize()
{
    GLuint program = loadShader("Flat", 2, ATTRIBUTE_VERTEX, "coord3d", ATTRIBUTE_TEXTURE0, "texcoord");

    //...
}


GLuint ShaderManager::loadShader(std::string shaderName, ... )
{
    GLuint program;

    //...

    va_list arglist;
    va_start(arglist, shaderName);

    int count = va_arg(arglist, int);
    for(int i = 0; i < count; i++) {
        AttributeLocation location = va_arg(arglist, AttributeLocation);
        char * name = va_arg(arglist, char *);
        glBindAttribLocation(program, location, name);
    }
    va_end(arglist);

    //...
}

Where both ATTRIBUTE_VERTEX and ATTRIBUTE_TExTURE are declared as

enum AttributeLocation {
        ATTRIBUTE_VERTEX = 0,
        ATTRIBUTE_COLOR,
        ATTRIBUTE_NORMAL,
        ATTRIBUTE_TEXTURE0
    };

But the program just terminates. I’ve found out, debugging the program, that the error occurs on the first line after the for loop. So I’m wondering if it is possible to do it or it’s something illegal.

Answer 1

This is because passing integral types that are less than sizeof(int) bytes big to a varargs function will convert them up to sizeof(int) bytes when passed on the stack. If AttributeLocation smaller than sizeof(int) bytes, then sizeof(int) bytes are pushed on the stack, but you retrieve only sizeof(AttributeLocation) bytes from the stack with the va_arg call. Then when you try to read the char*, you get the rest of the bytes of the AttributeLocation and some of the bytes of the const char* that you passed.