getgrent_r(3)

1GETGRENT_R(3)              Linux Programmer's Manual             GETGRENT_R(3)
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NAME

6       getgrent_r, fgetgrent_r - get group file entry reentrantly
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SYNOPSIS

9       #include <grp.h>
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11       int getgrent_r(struct group *gbuf, char *buf,
12                      size_t buflen, struct group **gbufp);
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14       int fgetgrent_r(FILE *fp, struct group *gbuf, char *buf,
15                       size_t buflen, struct group **gbufp);
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       getgrent_r(): _GNU_SOURCE
20       fgetgrent_r(): _SVID_SOURCE
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DESCRIPTION

23       The functions getgrent_r() and fgetgrent_r() are the reentrant versions
24       of getgrent(3) and fgetgrent(3).  The former reads the next group entry
25       from  the stream initialized by setgrent(3).  The latter reads the next
26       group entry from the stream fp.
27
28       The group structure is defined in <grp.h> as follows:
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30           struct group {
31               char    *gr_name;     /* group name */
32               char    *gr_passwd;   /* group password */
33               gid_t    gr_gid;      /* group ID */
34               char   **gr_mem;      /* group members */
35           };
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37       The nonreentrant functions return a pointer to  static  storage,  where
38       this  static  storage contains further pointers to group name, password
39       and members.  The reentrant functions described here return all of that
40       in caller-provided buffers.  First of all there is the buffer gbuf that
41       can hold a struct group.  And next the buffer buf of size  buflen  that
42       can hold additional strings.  The result of these functions, the struct
43       group read from the stream, is stored in the provided buffer *gbuf, and
44       a pointer to this struct group is returned in *gbufp.
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RETURN VALUE

47       On  success,  these  functions  return 0 and *gbufp is a pointer to the
48       struct group.  On error, these functions  return  an  error  value  and
49       *gbufp is NULL.
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ERRORS

52       ENOENT No more entries.
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54       ERANGE Insufficient  buffer space supplied.  Try again with larger buf‐
55              fer.
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CONFORMING TO

58       These functions are GNU extensions, done  in  a  style  resembling  the
59       POSIX  version of functions like getpwnam_r(3).  Other systems use pro‐
60       totype
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62           struct group *getgrent_r(struct group *grp, char *buf,
63                                    int buflen);
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65       or, better,
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67           int getgrent_r(struct group *grp, char *buf, int buflen,
68                          FILE **gr_fp);
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NOTES

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

75       #define _GNU_SOURCE
76       #include <grp.h>
77       #include <stdio.h>
78       #include <stdlib.h>
79       #define BUFLEN 4096
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81       int
82       main(void)
83       {
84           struct group grp, *grpp;
85           char buf[BUFLEN];
86           int i;
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88           setgrent();
89           while (1) {
90               i = getgrent_r(&grp, buf, BUFLEN, &grpp);
91               if (i)
92                   break;
93               printf("%s (%d):", grpp->gr_name, grpp->gr_gid);
94               for (i = 0; ; i++) {
95                   if (grpp->gr_mem[i] == NULL)
96                       break;
97                   printf(" %s", grpp->gr_mem[i]);
98               }
99               printf("\n");
100           }
101           endgrent();
102           exit(EXIT_SUCCESS);
103       }
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COLOPHON

110       This page is part of release 3.25 of the Linux  man-pages  project.   A
111       description  of  the project, and information about reporting bugs, can
112       be found at http://www.kernel.org/doc/man-pages/.
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116GNU                               2007-07-26                     GETGRENT_R(3)