#include <grp.h> int getgrent_r(struct group *gbuf, char *buf,
size_t buflen, struct group **gbufp); int fgetgrent_r(FILE *stream, struct group *gbuf, char *buf,
size_t buflen, struct group **gbufp);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getgrent_r():
_GNU_SOURCE
fgetgrent_r():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_SVID_SOURCE
The group structure is defined in <grp.h> as follows:
struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
gid_t gr_gid; /* group ID */
char **gr_mem; /* NULL-terminated array of pointers
to names of group members */
};
For more information about the fields of this structure, see group(5).
The nonreentrant functions return a pointer to static storage, where this static storage contains further pointers to group name, password and members. The reentrant functions described here return all of that in caller-provided buffers. First of all there is the buffer gbuf that can hold a struct group. And next the buffer buf of size buflen that can hold additional strings. The result of these functions, the struct group read from the stream, is stored in the provided buffer *gbuf, and a pointer to this struct group is returned in *gbufp.
| Interface | Attribute | Value |
| getgrent_r() | Thread safety | MT-Unsafe race:grent locale |
| fgetgrent_r() | Thread safety | MT-Safe |
In the above table, grent in race:grent signifies that if any of the functions setgrent(), getgrent(), endgrent(), or getgrent_r() are used in parallel in different threads of a program, then data races could occur.
struct group *getgrent_r(struct group *grp, char *buf,
int buflen);
or, better,
int getgrent_r(struct group *grp, char *buf, int buflen,
FILE **gr_fp);
#define _GNU_SOURCE #include <grp.h> #include <stdio.h> #include <stdlib.h> #define BUFLEN 4096 int main(void) { struct group grp, *grpp; char buf[BUFLEN]; int i; setgrent(); while (1) { i = getgrent_r(&grp, buf, BUFLEN, &grpp); if (i) break; printf("%s (%d):", grpp->gr_name, grpp->gr_gid); for (i = 0; ; i++) { if (grpp->gr_mem[i] == NULL) break; printf(" %s", grpp->gr_mem[i]); } printf("\n"); } endgrent(); exit(EXIT_SUCCESS); }