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cuserid(3) [netbsd man page]

CUSERID(3)						   BSD Library Functions Manual 						CUSERID(3)

NAME
cuserid -- get user name LIBRARY
Compatibility Library (libcompat, -lcompat) SYNOPSIS
#include <stdio.h> char * cuserid(char *buf); DESCRIPTION
This interface is available from the compatibility library, libcompat and has been obsoleted by getlogin(2). The cuserid() function returns a character string representation of the user name associated with the effective user ID of the calling process. If buf is not the NULL pointer, the user name is copied into the memory referenced by buf. The argument buf is assumed to point to an array at least L_cuserid (as defined in the include file <stdio.h>) bytes long. Otherwise, the user name is copied to a static buffer. RETURN VALUES
If buf is not the NULL pointer, buf is returned; otherwise the address of the static buffer is returned. If the user name could not be determined, if buf is not the NULL pointer, the null character '' will be stored at *buf; otherwise the NULL pointer is returned. SEE ALSO
getlogin(2), getpwent(3) STANDARDS
The cuserid() function conforms to IEEE Std 1003.1-1988 (``POSIX.1''). BUGS
Due to irreconcilable differences in historic implementations, cuserid() was removed from the ISO/IEC 9945-1:1990 (``POSIX.1'') standard. This implementation exists purely for compatibility with existing programs. New programs should use one of the following three alternatives to obtain the user name: 1. getlogin() to return the user's login name. 2. getpwuid(geteuid()) to return the user name associated with the calling process' effective user ID. 3. getpwuid(getuid()) to return the user name associated with the calling process' real user ID. BSD
November 28, 1993 BSD

Check Out this Related Man Page

GETLOGIN(3)						     Linux Programmer's Manual						       GETLOGIN(3)

NAME
getlogin, cuserid - get user name SYNOPSIS
#include <unistd.h> char *getlogin(void); #include <stdio.h> char *cuserid(char *string); DESCRIPTION
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. cuserid returns a pointer to a string containing a user name 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 user name. 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 setuid 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. ERRORS
ENOMEM Insufficient memory to allocate passwd structure. FILES
/etc/passwd password database file /var/run/utmp (traditionally /etc/utmp; some libc versions used /var/adm/utmp) CONFORMING TO
POSIX.1. System V has a cuserid function which uses the real user ID rather than the effective user ID. The cuserid function was included in the 1988 version of POSIX, but removed from the 1990 version. BUGS
Unfortunately, it is often rather easy to fool getlogin(). Sometimes it does not work at all, because some program messed up the utmp file. Often, it gives only the first 8 characters of the login name. The user currently logged in on the controlling tty of our program need not be the user who started it. Avoid getlogin() for security-related purposes. Nobody knows precisely what cuserid() does - avoid it in portable programs - avoid it altogether - use getpwuid(geteuid()) instead, if that is what you meant. DO NOT USE cuserid(). SEE ALSO
geteuid(2), getuid(2) Linux 1.2.13 1995-09-03 GETLOGIN(3)
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