Manpages - getpwent_r.3

getpwent_r, fgetpwent_r - get passwd file entry reentrantly

  #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",structpasswd*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

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.

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.

ENOENT

No more entries.

ERANGE

Insufficient buffer space supplied. Try again with larger buffer.

For an explanation of the terms used in this section, see *attributes*(7).

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.

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);

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

  #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);
  }

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

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