define extern variable inside a function

Question

Lets say I have an extern function pointer in a header file

extern void (__stdcall * const glEnable) (GLenum cap);

is there a way to define it inside a function, because its definition depends on other stuff

void glInit()
{
    ...
    Lib lib = loadLib("opengl");
    glEnable = procAddr(lib, "glEnable");
    ...
}

to define it inside a function No it is not possible - symbols declared at file scope have to be defined at file scope. I do not believe such an answer solves your real underlying problem in any way... are you asking an XY question? — KamilCuk
– KamilCuk, Commented Jun 1, 2021 at 20:16
Are you aware of the difference of declaring, defining and initialising a variable? — Yunnosch
– Yunnosch, Commented Jun 1, 2021 at 20:22
It's unclear what initialization needs to be done on a function pointer. Could you show us how you'd like this to work so we can see the "other stuff"? — Schwern
– Schwern, Commented Jun 1, 2021 at 20:24

Aykhan Hagverdili · Accepted Answer · 2021-06-01 20:34:42Z

1

You can do this:

// .h file
extern void (__stdcall * glEnable) (GLenum cap);


// .c file
void (__stdcall * glEnable) (GLenum cap) = NULL;

void glInit()
{
    Lib lib = loadLib("opengl");
    glEnable = procAddr(lib, "glEnable");
}

Now, the function pointer is null until someone calls glInit. It is undefined behavior to call that function pointer before calling glInit, and I assume that was your intention anyway.

edited Jun 1, 2021 at 20:34

answered Jun 1, 2021 at 20:29

Aykhan Hagverdili

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