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.
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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       For more information about the fields of this structure, see group(5).
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39       The nonreentrant functions return a pointer to  static  storage,  where
40       this  static  storage contains further pointers to group name, password
41       and members.  The reentrant functions described here return all of that
42       in caller-provided buffers.  First of all there is the buffer gbuf that
43       can hold a struct group.  And next the buffer buf of size  buflen  that
44       can hold additional strings.  The result of these functions, the struct
45       group read from the stream, is stored in the provided buffer *gbuf, and
46       a pointer to this struct group is returned in *gbufp.
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RETURN VALUE

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

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

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

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

77       #define _GNU_SOURCE
78       #include <grp.h>
79       #include <stdio.h>
80       #include <stdlib.h>
81       #define BUFLEN 4096
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83       int
84       main(void)
85       {
86           struct group grp, *grpp;
87           char buf[BUFLEN];
88           int i;
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90           setgrent();
91           while (1) {
92               i = getgrent_r(&grp, buf, BUFLEN, &grpp);
93               if (i)
94                   break;
95               printf("%s (%d):", grpp->gr_name, grpp->gr_gid);
96               for (i = 0; ; i++) {
97                   if (grpp->gr_mem[i] == NULL)
98                       break;
99                   printf(" %s", grpp->gr_mem[i]);
100               }
101               printf("\n");
102           }
103           endgrent();
104           exit(EXIT_SUCCESS);
105       }
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COLOPHON

112       This page is part of release 3.53 of the Linux  man-pages  project.   A
113       description  of  the project, and information about reporting bugs, can
114       be found at http://www.kernel.org/doc/man-pages/.
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118GNU                               2010-10-21                     GETGRENT_R(3)