How can I calculate the complete buffer size for GetModuleFileName?

Question

The GetModuleFileName() takes a buffer and size of buffer as input; however its return value can only tell us how many characters is has copied, and if the size is not enoug

Answer 1

Using

extern char* _pgmptr

might work.

From the documentation of GetModuleFileName:

The global variable _pgmptr is automatically initialized to the full path of the executable file, and can be used to retrieve the full path name of an executable file.

But if I read about _pgmptr:

When a program is not run from the command line, _pgmptr might be initialized to the program name (the file's base name without the file name extension) or to a file name, relative path, or full path.

Anyone who knows how _pgmptr is initialized? If SO had support for follow-up questions I would posted this question as a follow up.