getpwent_r(3)

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

NAME
       getpwent_r, fgetpwent_r - get passwd file entry reentrantly

SYNOPSIS
       #include <pwd.h>

       int getpwent_r(struct passwd *pwbuf, char *buf,
                      size_t buflen, struct passwd **pwbufp);

       int fgetpwent_r(FILE *stream, struct passwd *pwbuf, char *buf,
                       size_t buflen, struct passwd **pwbufp);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getpwent_r(),
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE || _SVID_SOURCE
       fgetpwent_r():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _SVID_SOURCE

DESCRIPTION
       The functions getpwent_r() and fgetpwent_r() are the reentrant versions
       of getpwent(3) and fgetpwent(3).  The former reads the next passwd  en-
       try  from  the stream initialized by setpwent(3).  The latter reads the
       next passwd entry from stream.

       The passwd structure is defined in <pwd.h> as follows:

           struct passwd {
               char    *pw_name;      /* username */
               char    *pw_passwd;    /* user password */
               uid_t    pw_uid;       /* user ID */
               gid_t    pw_gid;       /* group ID */
               char    *pw_gecos;     /* user information */
               char    *pw_dir;       /* home directory */
               char    *pw_shell;     /* shell program */
           };

       For more information about the fields of this structure, see passwd(5).

       The nonreentrant functions return a pointer to  static  storage,  where
       this  static  storage contains further pointers to user name, password,
       gecos field, home directory and shell.   The  reentrant  functions  de-
       scribed  here  return all of that in caller-provided buffers.  First of
       all there is the buffer pwbuf that can hold a struct passwd.  And  next
       the  buffer  buf  of size buflen that can hold additional strings.  The
       result of these functions, the struct passwd read from the  stream,  is
       stored  in  the  provided  buffer  *pwbuf, and a pointer to this struct
       passwd is returned in *pwbufp.

RETURN VALUE
       On success, these functions return 0 and *pwbufp is a  pointer  to  the
       struct  passwd.   On  error,  these functions return an error value and
       *pwbufp is NULL.

ERRORS
       ENOENT No more entries.

       ERANGE Insufficient buffer space supplied.  Try again with larger  buf-
              fer.

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(7).

       +--------------+---------------+-----------------------------+
       |Interface     | Attribute     | Value                       |
       +--------------+---------------+-----------------------------+
       |getpwent_r()  | Thread safety | MT-Unsafe race:pwent locale |
       +--------------+---------------+-----------------------------+
       |fgetpwent_r() | Thread safety | MT-Safe                     |
       +--------------+---------------+-----------------------------+
       In the above table, pwent in race:pwent signifies that if  any  of  the
       functions  setpwent(), getpwent(), endpwent(), or getpwent_r() are used
       in parallel in different threads of a program, then  data  races  could
       occur.

CONFORMING TO
       These  functions  are  GNU  extensions,  done in a style resembling the
       POSIX version of functions like getpwnam_r(3).  Other systems  use  the
       prototype

           struct passwd *
           getpwent_r(struct passwd *pwd, char *buf, int buflen);

       or, better,

           int
           getpwent_r(struct passwd *pwd, char *buf, int buflen,
                      FILE **pw_fp);

NOTES
       The  function  getpwent_r() is not really reentrant since it shares the
       reading position in the stream with all other threads.

EXAMPLES
       #define _GNU_SOURCE
       #include <pwd.h>
       #include <stdio.h>
       #define BUFLEN 4096

       int
       main(void)
       {
           struct passwd pw, *pwp;
           char buf[BUFLEN];
           int i;

           setpwent();
           while (1) {
               i = getpwent_r(&pw, buf, BUFLEN, &pwp);
               if (i)
                   break;
               printf("%s (%d)\tHOME %s\tSHELL %s\n", pwp->pw_name,
                      pwp->pw_uid, pwp->pw_dir, pwp->pw_shell);
           }
           endpwent();
           exit(EXIT_SUCCESS);
       }

SEE ALSO
       fgetpwent(3), getpw(3), getpwent(3),  getpwnam(3),  getpwuid(3),  putp-
       went(3), passwd(5)

COLOPHON
       This  page  is  part of release 5.07 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

GNU                               2020-06-09                     GETPWENT_R(3)