should I free pointer returned by getpwuid() in Linux?

Question

Hi,

After I call getpwuid(uid), I have a reference to a pointer. Should I free that when I don't use it anymore? Reading the man pages, it says that it makes reference to some static area, that may be overwritten by subsequent calls to the same functions, so I'm sure sure if I should touch that memory area.

Thanks.

Answer 1

Actually it returns a pointer to an already existing structure, so you should not free it.

Answer 2

No. You do not need to free the result. You can only call free(3) on pointers allocated on the heap with malloc(3), calloc(3) or realloc(3).

Static data is part of a program's data or bss segments and will persist until the process exits (or is overwritten by exec(2)).

Answer 3

Use the *_r functions (getpwuid_r()) for thread-safe (reentrant) functions that allow you to supply the buffer space to place the returned information in. Be sure check errno for success or failure. If you do not use reentrant functions you can safely assume that the function returns data that does not need to be freed, but will also be overwritten by successive calls to the same function.