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[thirdparty/man-pages.git] / man3 / getgrent_r.3

.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
.\"
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.\" USA.
.\"
.TH GETGRENT 3 2003-11-15 "GNU" "Linux Programmer's Manual"
.SH NAME
getgrent_r, fgetgrent_r \- get group file entry reentrantly
.SH SYNOPSIS
.nf
.B "#define _GNU_SOURCE"
.br
.B #include <grp.h>
.sp
.BI "int getgrent_r(struct group *" gbuf ", char *" buf ,
.br
.BI "               size_t " buflen ", struct group **" gbufp );
.sp
.BI "int fgetgrent_r(FILE *" fp ", struct group *" gbuf ", char *" buf ,
.br
.BI "                size_t " buflen ", struct group **" gbufp );
.SH DESCRIPTION
The functions
.BR getgrent_r ()
and
.BR fgetgrent_r ()
are the reentrant versions of
.BR getgrent (3)
and
.BR fgetgrent (3).
The former reads the next group entry from the stream initialized by
.BR setgrent (3).
The latter reads the next group entry from the stream
.I fp
given as parameter.
.PP
The \fIgroup\fP structure is defined in
.I <grp.h>
as follows:
.sp
.RS
.nf
struct group {
    char    *gr_name;      /* group name */
    char    *gr_passwd;    /* group password */
    gid_t   gr_gid;        /* group ID */
    char    **gr_mem;      /* group members */
};
.ta
.fi
.RE
.sp
The non-reentrant 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
.I gbuf
that can hold a struct group.
And next the buffer
.I buf
of size
.I buflen
that can hold additional strings.
The result of these functions, the struct group read from the stream,
is stored in the provided buffer
.RI * gbuf ,
and a pointer to this struct group is returned in
.RI * gbufp .
.SH "RETURN VALUE"
On success, these functions return 0 and
.RI * gbufp
is a pointer to the struct group.
On error, these functions return an error value and
.RI * gbufp
is NULL.
.SH ERRORS
.TP
.B ENOENT
No more entries.
.TP
.B ERANGE
Insufficient buffer space supplied.
Try again with larger buffer.
.SH EXAMPLE
.nf
#define _GNU_SOURCE
#include <grp.h>
#include <stdio.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("\en");
    }
    endgrent();
    return 0;
}
.fi
.\" perhaps add error checking - should use strerror_r
.\" #include <errno.h>
.\" #include <stdlib.h>
.\"         if (i) {
.\"               if (i == ENOENT)
.\"                     break;
.\"               printf("getgrent_r: %s", strerror(i));
.\"               exit(1);
.\"         }
.SH "CONFORMING TO"
These functions are GNU extensions, done in a style resembling
the POSIX version of functions like
.BR getpwnam_r (3).
Other systems use prototype
.sp
.nf
.in +4
struct group *
getgrent_r(struct group *grp, char *buf, int buflen);
.in
.fi
.sp
or, better,
.sp
.nf
.in +4
int
getgrent_r(struct group *grp, char *buf, int buflen,
           FILE **gr_fp);
.in
.fi
.SH NOTES
The function
.BR getgrent_r ()
is not really reentrant since it shares the reading position
in the stream with all other threads.
.SH "SEE ALSO"
.BR fgetgrent (3),
.BR getgrent (3),
.BR getgrgid (3),
.BR getgrnam (3),
.BR putgrent (3),
.BR group (5),
.BR feature_test_macros (7)