getlogin, getlogin_r, cuserid - get username
#include <unistd.h>
char *getlogin(void);
int getlogin_r(char buf[.bufsize], size_t bufsize);
#include <stdio.h>
char *cuserid(char *string);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getlogin() returns a pointer to a string containing the name of the user logged in on the controlling terminal of the process, or a null pointer if this information cannot be determined. The string is statically allocated and might be overwritten on subsequent calls to this function or to cuserid().
getlogin_r() returns this same username in the array
buf of size bufsize.
cuserid() returns a pointer to a string containing a
username associated with the effective user ID of the process. If
string is not a null pointer, it should be an array that can
hold at least L_cuserid characters; the string is
returned in this array. Otherwise, a pointer to a string in a static
area is returned. This string is statically allocated and might be
overwritten on subsequent calls to this function or to
getlogin().
The macro L_cuserid is an integer constant that
indicates how long an array you might need to store a username.
L_cuserid is declared in <stdio.h>.
These functions let your program identify positively the user who is running (cuserid()) or the user who logged in this session (getlogin()). (These can differ when set-user-ID programs are involved.)
For most purposes, it is more useful to use the environment variable LOGNAME to find out who the user is. This is more flexible precisely because the user can set LOGNAME arbitrarily.
getlogin() returns a pointer to the username when
successful, and NULL on failure, with errno set to indicate the
error. getlogin_r() returns 0 when successful, and
nonzero on failure.