man3/getpwent_r.3

   1 .\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
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  23 .TH GETPWENT_R 3 2003-11-15 "GNU" "Linux Programmer's Manual"
  24 .SH NAME
  25 getpwent_r, fgetpwent_r \- get passwd file entry reentrantly
  26 .SH SYNOPSIS
  27 .nf
  28 .B "#define _GNU_SOURCE"
  29 .br
  30 .B #include <pwd.h>
  31 .sp
  32 .BI "int getpwent_r(struct passwd *" pwbuf ", char *" buf ,
  33 .br
  34 .BI "               size_t " buflen ", struct passwd **" pwbufp );
  35 .sp
  36 .BI "int fgetpwent_r(FILE *" fp ", struct passwd *" pwbuf ", char *" buf ,
  37 .br
  38 .BI "                size_t " buflen ", struct passwd **" pwbufp );
  39 .SH DESCRIPTION
  40 The functions
  41 .BR getpwent_r ()
  42 and
  43 .BR fgetpwent_r ()
  44 are the reentrant versions of
  45 .BR getpwent (3)
  46 and
  47 .BR fgetpwent (3).
  48 The former reads the next passwd entry from the stream initialized by
  49 .BR setpwent (3).
  50 The latter reads the next passwd entry from the stream
  51 .I fp
  52 given as parameter.
  53 .PP
  54 The \fIpasswd\fP structure is defined in
  55 .I <pwd.h>
  56 as follows:
  57 .sp
  58 .RS
  59 .nf
  60 struct passwd {
  61     char    *pw_name;      /* user name */
  62     char    *pw_passwd;    /* user password */
  63     uid_t    pw_uid;       /* user ID */
  64     gid_t    pw_gid;       /* group ID */
  65     char    *pw_gecos;     /* real name */
  66     char    *pw_dir;       /* home directory */
  67     char    *pw_shell;     /* shell program */
  68 };
  69 .fi
  70 .RE
  71 .sp
  72 The non-reentrant functions return a pointer to static storage,
  73 where this static storage contains further pointers to user
  74 name, password, gecos field, home directory and shell.
  75 The reentrant functions described here return all of that in
  76 caller-provided buffers.
  77 First of all there is the buffer
  78 .I pwbuf
  79 that can hold a struct passwd.
  80 And next the buffer
  81 .I buf
  82 of size
  83 .I buflen
  84 that can hold additional strings.
  85 The result of these functions, the struct passwd read from the stream,
  86 is stored in the provided buffer
  87 .RI * pwbuf ,
  88 and a pointer to this struct passwd is returned in
  89 .RI * pwbufp .
  90 .SH "RETURN VALUE"
  91 On success, these functions return 0 and
  92 .RI * pwbufp
  93 is a pointer to the struct passwd.
  94 On error, these functions return an error value and
  95 .RI * pwbufp
  96 is NULL.
  97 .SH ERRORS
  98 .TP
  99 .B ENOENT
 100 No more entries.
 101 .TP
 102 .B ERANGE
 103 Insufficient buffer space supplied.
 104 Try again with larger buffer.
 105 .SH EXAMPLE
 106 .nf
 107 #define _GNU_SOURCE
 108 #include <pwd.h>
 109 #include <stdio.h>
 110 #define BUFLEN 4096
 111
 112 int
 113 main(void)
 114 {
 115     struct passwd pw, *pwp;
 116     char buf[BUFLEN];
 117     int i;
 118
 119     setpwent();
 120     while (1) {
 121         i = getpwent_r(&pw, buf, BUFLEN, &pwp);
 122         if (i)
 123             break;
 124         printf("%s (%d)\etHOME %s\etSHELL %s\en", pwp->pw_name,
 125                pwp->pw_uid, pwp->pw_dir, pwp->pw_shell);
 126     }
 127     endpwent();
 128     return 0;
 129 }
 130 .fi
 131 .\" perhaps add error checking - should use strerror_r
 132 .\" #include <errno.h>
 133 .\" #include <stdlib.h>
 134 .\"         if (i) {
 135 .\"               if (i == ENOENT)
 136 .\"                     break;
 137 .\"               printf("getpwent_r: %s", strerror(i));
 138 .\"               exit(1);
 139 .\"         }
 140 .SH "CONFORMING TO"
 141 These functions are GNU extensions, done in a style resembling
 142 the POSIX version of functions like
 143 .BR getpwnam_r (3).
 144 Other systems use prototype
 145 .sp
 146 .nf
 147 .in +4
 148 struct passwd *
 149 getpwent_r(struct passwd *pwd, char *buf, int buflen);
 150 .in
 151 .fi
 152 .sp
 153 or, better,
 154 .sp
 155 .nf
 156 .in +4
 157 int
 158 getpwent_r(struct passwd *pwd, char *buf, int buflen,
 159            FILE **pw_fp);
 160 .in
 161 .fi
 162 .SH NOTES
 163 The function
 164 .BR getpwent_r ()
 165 is not really reentrant since it shares the reading position
 166 in the stream with all other threads.
 167 .SH "SEE ALSO"
 168 .BR fgetpwent (3),
 169 .BR getpw (3),
 170 .BR getpwent (3),
 171 .BR getpwnam (3),
 172 .BR getpwuid (3),
 173 .BR putpwent (3),
 174 .BR passwd (5),
 175 .BR feature_test_macros (7)