getpwent_r(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

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

NAME         top

       getpwent_r, fgetpwent_r - get passwd file entry reentrantly

SYNOPSIS         top

       #include <pwd.h>

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

       The functions getpwent_r() and fgetpwent_r() are the reentrant
       versions of getpwent(3) and fgetpwent(3).  The former reads the
       next passwd entry 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 described 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         top

       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         top

       ENOENT No more entries.

       ERANGE Insufficient buffer space supplied.  Try again with larger
              buffer.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(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         top

       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         top

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

EXAMPLES         top

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

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

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

SEE ALSO         top

       fgetpwent(3), getpw(3), getpwent(3), getpwnam(3), getpwuid(3),
       putpwent(3), passwd(5)

COLOPHON         top

       This page is part of release 5.13 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                            2021-03-22                  GETPWENT_R(3)

Pages that refer to this page: fgetpwent(3)getpwent(3)genhomedircon(8)