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fgetgrent_r (3)
  • >> fgetgrent_r (3) ( Linux man: Библиотечные вызовы )
  •  

    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 *fp, 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(): _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 the stream fp.

    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;      /* group members */
    };
    

    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 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.  

    RETURN VALUE

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

    ERRORS

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

    CONFORMING TO

    These functions are GNU extensions, done in a style resembling the POSIX version of functions like getpwnam_r(3). Other systems use 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)  

    COLOPHON

    This page is part of release 3.14 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


     

    Index

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


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