#include <stdio.h> char *cuserid(char *s);
The cuserid() function generates a character-string representation of the login name under which the owner of the current process is logged in. If s is a null pointer, this representation is generated in an internal static area whose address is returned. Otherwise, s is assumed to point to an array of at least L_cuserid characters; the representation is left in this array. The constant L_cuserid is defined in the <stdio.h> header.
In multithreaded applications, the caller must always supply an array s for the return value.
If the login name cannot be found, cuserid() returns a null pointer. If s is not a null pointer, the null character `\0' will be placed at s.
See attributes(5) for descriptions of the following attributes: