fgetpwent_r(3) -- Linux man page

 

NAME

getpwent_r, fgetpwent_r - get passwd file entry reentrantly  

SYNOPSIS

#define _GNU_SOURCE

#include <pwd.h> int getpwent_r(struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp); int fgetpwent_r(FILE *fp, struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp);
 

DESCRIPTION

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 the stream fp given as parameter.

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

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

The non-reentrant 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

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 buffer.
 

EXAMPLE

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

int main() {
      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();
      return 0;
}
 

CONFORMING TO

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

SEE ALSO

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