Manpage of GETGRENT_R

GETGRENT_R

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

getgrent_r, fgetgrent_r - get group file entry reentrantly  

SYNOPSIS

#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  

DESCRIPTION

The functions getgrent_r() and fgetgrent_r() are the reentrant versions of getgrent(3) and fgetgrent(3). The former reads the next group entry from the stream initialized by setgrent(3). The latter reads the next group entry from stream.

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 gbufthat can hold a struct group. And next the buffer bufof size buflenthat 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.  

RETURN VALUE

On success, these functions return 0 and *gbufpis a pointer to the struct group. On error, these functions return an error value and *gbufpis NULL.  

ERRORS

ENOENT
No more entries.
ERANGE
Insufficient buffer space supplied. Try again with larger buffer.
 

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
getgrent_r() Thread safetyMT-Unsafe race:grent locale
fgetgrent_r() Thread safetyMT-Safe

In the above table, grentin race:grentsignifies 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.  

CONFORMING TO

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 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);
 

NOTES

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

EXAMPLE

#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);
}
 

SEE ALSO

fgetgrent(3), getgrent(3), getgrgid(3), getgrnam(3), putgrent(3), group(5)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO

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