The getpwnam function returns information about a user database
entry for the specified name.
The getpwnam_r function is a reentrant version of getpwnam.
Format
#include <pwd.h>
struct passwd *getpwnam (const char *name); (ISO POSIX-1)
struct passwd *getpwnam (const char *name, . . . );
(DEC C Extension)
int getpwnam_r (const char *name, struct passwd *pwd,
char *buffer, size_t bufsize, struct
passwd **result); (ISO POSIX-1),
(Integrity servers, Alpha)
int getpwnam_r (const char *name, struct passwd *pwd,
char *buffer, size_t bufsize, struct
passwd **result, . . . ); (DEC C Extension),
(Integrity servers, Alpha)
1 – Function Variants
The getpwnam and getpwnam_r functions have variants named __32_
getpwnam, _getpwnam_r32 and __64_getpwnam, _getpwnam_r64 for use
with 32-bit and 64-bit pointer sizes, respectively.
2 – Arguments
name
The name of the user for which the attributes are to be read.
pwd
The address of a passwd structure into which the function writes
its results.
buffer
A working buffer for the result argument that is able to hold the
largest entry in the passwd structure. Storage referenced by the
passwd structure is allocated from the memory provided with the
buffer argument, which is bufsize characters in length.
bufsize
The length of the character array that buffer points to.
result
Upon successful return, is set to pwd. Upon unsuccessful return,
the result is set to NULL.
. . .
An optional argument that can be either 1 or 0. If you specify
1, the directory specification is returned in OpenVMS format. If
you specify 0, the directory specification (pathname) is returned
in UNIX style format. If you omit this argument, the function
returns the directory specification according to your current
command-language interpreter.
3 – Description
The getpwnam function searches the user database for an entry
with the specified name. The function returns the first user
entry in the database with the pw_name member of the passwd
structure that matches the name argument.
The passwd structure is defined in the <pwd.h> header file as
follows:
pw_name The user's login name.
pw_uid The numerical user ID.
pw_gid The numerical group ID.
pw_dir The home directory of the user.
pw_shell The initial program for the user.
NOTE
All information generated by the getpwnam function is stored
in a per-thread static area and is overwritten on subsequent
calls to the function.
The getpwnam_r function is the reentrant version of getpwnam.
The getpwnam_r function updates the passwd structure pointed to
by pwd and stores a pointer to that structure at the location
pointed to by result. The structure will contain an entry from
the user database that matches the specified name. Storage
referenced by the structure is allocated from the memory provided
with the buffer argument, which is bufsize characters in length.
The maximum size needed for this buffer can be determined with
the _SC_GETPW_R_SIZE_MAX parameter of the sysconf function. On
error or if the requested entry is not found, a NULL pointer is
returned at the location pointed to by result.
Applications wishing to check for error situations should set
errno to 0 before calling getpwnam. If getpwnam returns a NULL
pointer and errno is nonzero, an error occurred.
4 – Return Values
x getpwnam returns a pointer to a valid passwd
structure, if a matching entry is found.
NULL getpwnam returns NULL if an error occurred
or a the specified entry was not found. errno
is set to indicate the error. The getpwnam
function may fail if:
o EIO - An I/O error has occurred.
o EINTR - A signal was intercepted during
getpwnam.
o EMFILE - OPEN_MAX file descriptors are
currently open in the calling process.
o ENFILE - The maximum allowable number of
files is currently open in the system.
0 When successful, getpwnam_r returns 0 and
stores a pointer to the updated passwd
structure at the location pointed to by
result.
0 When unsuccessful (on error or if the
requested entry is not found), getpwnam_r
returns 0 and stores a NULL pointer at the
location pointed to by result. The getpwnam_r
function may fail if:
o ERANGE - Insufficient storage was supplied
through buffer and bufsize to contain the
data to be referenced by the resulting
passwd structure.
5 – Example
When building a sample program with /def=_USE_STD_STAT, you can
observe the following:
o When the DECC$POSIX_STYLE_UID logical is enabled:
- For a system, that supports POSIX style identifiers:
- getpwnam_r API reads information from the TCP/IP proxy
database and fills UID and GID with values from the
TCP/IP proxy database.
- getgrgid_r API returns gr_name and gr_mem from
the right's database associated with GID returned by
getpwnam_r API.
- System with no support for POSIX style identifiers,
getpwnam_r fills GID and UID with SYSGEN parameters as
"DEFUID" and "DEFGID".
o When the DECC$POSIX_STYLE_UID logical is not defined:
getpwnam function returns information about a user database
entry for the specified name, which is specified in
SYSUAF.DAT
#include <unistd> // getuid()
#include <pwd> // getpwuid_r()
#include <grp>
#include <errno.h>
#include <stdio.h>
#include <string.h>
main()
{
struct passwd pwd2;
const unsigned int PWD_BUFF_SIZE = 1024;
const unsigned int GRP_BUFF_SIZE = 1024;
struct passwd *p_passwd;
struct passwd *result;
struct group *grpresult;
struct group grp;
char pwdBuffer[PWD_BUFF_SIZE],*name;
char grpBuffer[GRP_BUFF_SIZE];
char buf[PWD_BUFF_SIZE];
gid_t gid;
uid_t uid;
int status;
p_passwd = getpwnam("user1");
uid=p_passwd->pw_uid;
gid=p_passwd->pw_gid;
printf("User id is %u\n", uid);
printf("Group id is %u\n", gid);
status = getpwnam_r("user1", &pwd2, pwdBuffer, PWD_BUFF_SIZE, &result);
gid = pwd2.pw_gid;
status = getgrgid_r(gid, &grp, grpBuffer, GRP_BUFF_SIZE, &grpresult);
gid=grp.gr_gid; name=grp.gr_name;
strcpy(name,grp.gr_name);
printf("Group id is %u\n", gid);
printf("Group name is %s\n", name);
}
Running the example program with /def=_USE_STD_STAT produces
the following result:
o When the DECC$POSIX_STYLE_UID logical is NOT enabled, prints
uid as 11010118 (result of 65536*168+ 70) and gid as 168
with group name as RTL.
o When the DECC$POSIX_STYLE_UID logical is enabled and POSIX
style identifiers are supported, prints uid as 70, gid as
168 with group name as FOR_POSIX_TEST (retrieved from TCP/IP
proxy database).
o When the DECC$POSIX_STYLE_UID logical is enabled, but POSIX
style identifiers are not supported, prints uid as DEFUID,
gid as DEFGID with group name as invalid buffer.