man3/getpwent_r.3

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  24 .TH GETPWENT_R 3 2016-03-15 "GNU" "Linux Programmer's Manual"
  25 .SH NAME
  26 getpwent_r, fgetpwent_r \- get passwd file entry reentrantly
  27 .SH SYNOPSIS
  28 .nf
  29 .B #include <pwd.h>
  30 .PP
  31 .BI "int getpwent_r(struct passwd *" pwbuf ", char *" buf ,
  32 .br
  33 .BI "               size_t " buflen ", struct passwd **" pwbufp );
  34 .PP
  35 .BI "int fgetpwent_r(FILE *" stream ", struct passwd *" pwbuf ", char *" buf ,
  36 .br
  37 .BI "                size_t " buflen ", struct passwd **" pwbufp );
  38 .fi
  39 .PP
  40 .in -4n
  41 Feature Test Macro Requirements for glibc (see
  42 .BR feature_test_macros (7)):
  43 .in
  44 .PP
  45 .BR getpwent_r (),
  46     Since glibc 2.19:
  47         _DEFAULT_SOURCE
  48     Glibc 2.19 and earlier:
  49         _BSD_SOURCE || _SVID_SOURCE
  50 .br
  51 .BR fgetpwent_r ():
  52     Since glibc 2.19:
  53         _DEFAULT_SOURCE
  54     Glibc 2.19 and earlier:
  55         _SVID_SOURCE
  56 .SH DESCRIPTION
  57 The functions
  58 .BR getpwent_r ()
  59 and
  60 .BR fgetpwent_r ()
  61 are the reentrant versions of
  62 .BR getpwent (3)
  63 and
  64 .BR fgetpwent (3).
  65 The former reads the next passwd entry from the stream initialized by
  66 .BR setpwent (3).
  67 The latter reads the next passwd entry from
  68 .IR stream .
  69 .PP
  70 The \fIpasswd\fP structure is defined in
  71 .I <pwd.h>
  72 as follows:
  73 .sp
  74 .in +4n
  75 .nf
  76 struct passwd {
  77     char    *pw_name;      /* username */
  78     char    *pw_passwd;    /* user password */
  79     uid_t    pw_uid;       /* user ID */
  80     gid_t    pw_gid;       /* group ID */
  81     char    *pw_gecos;     /* user information */
  82     char    *pw_dir;       /* home directory */
  83     char    *pw_shell;     /* shell program */
  84 };
  85 .fi
  86 .in
  87 .PP
  88 For more information about the fields of this structure, see
  89 .BR passwd (5).
  90
  91 The nonreentrant functions return a pointer to static storage,
  92 where this static storage contains further pointers to user
  93 name, password, gecos field, home directory and shell.
  94 The reentrant functions described here return all of that in
  95 caller-provided buffers.
  96 First of all there is the buffer
  97 .I pwbuf
  98 that can hold a \fIstruct passwd\fP.
  99 And next the buffer
 100 .I buf
 101 of size
 102 .I buflen
 103 that can hold additional strings.
 104 The result of these functions, the \fIstruct passwd\fP read from the stream,
 105 is stored in the provided buffer
 106 .IR *pwbuf ,
 107 and a pointer to this \fIstruct passwd\fP is returned in
 108 .IR *pwbufp .
 109 .SH RETURN VALUE
 110 On success, these functions return 0 and
 111 .I *pwbufp
 112 is a pointer to the \fIstruct passwd\fP.
 113 On error, these functions return an error value and
 114 .I *pwbufp
 115 is NULL.
 116 .SH ERRORS
 117 .TP
 118 .B ENOENT
 119 No more entries.
 120 .TP
 121 .B ERANGE
 122 Insufficient buffer space supplied.
 123 Try again with larger buffer.
 124 .SH ATTRIBUTES
 125 For an explanation of the terms used in this section, see
 126 .BR attributes (7).
 127 .TS
 128 allbox;
 129 lb lb lbw27
 130 l l l.
 131 Interface       Attribute       Value
 132 T{
 133 .BR getpwent_r ()
 134 T}      Thread safety   MT-Unsafe race:pwent locale
 135 T{
 136 .BR fgetpwent_r ()
 137 T}      Thread safety   MT-Safe
 138 .TE
 139
 140 In the above table,
 141 .I pwent
 142 in
 143 .I race:pwent
 144 signifies that if any of the functions
 145 .BR setpwent (),
 146 .BR getpwent (),
 147 .BR endpwent (),
 148 or
 149 .BR getpwent_r ()
 150 are used in parallel in different threads of a program,
 151 then data races could occur.
 152 .SH CONFORMING TO
 153 These functions are GNU extensions, done in a style resembling
 154 the POSIX version of functions like
 155 .BR getpwnam_r (3).
 156 Other systems use the prototype
 157 .sp
 158 .nf
 159 .in +4n
 160 struct passwd *
 161 getpwent_r(struct passwd *pwd, char *buf, int buflen);
 162 .in
 163 .fi
 164 .sp
 165 or, better,
 166 .sp
 167 .nf
 168 .in +4n
 169 int
 170 getpwent_r(struct passwd *pwd, char *buf, int buflen,
 171            FILE **pw_fp);
 172 .in
 173 .fi
 174 .SH NOTES
 175 The function
 176 .BR getpwent_r ()
 177 is not really reentrant since it shares the reading position
 178 in the stream with all other threads.
 179 .SH EXAMPLE
 180 .nf
 181 #define _GNU_SOURCE
 182 #include <pwd.h>
 183 #include <stdio.h>
 184 #define BUFLEN 4096
 185
 186 int
 187 main(void)
 188 {
 189     struct passwd pw, *pwp;
 190     char buf[BUFLEN];
 191     int i;
 192
 193     setpwent();
 194     while (1) {
 195         i = getpwent_r(&pw, buf, BUFLEN, &pwp);
 196         if (i)
 197             break;
 198         printf("%s (%d)\etHOME %s\etSHELL %s\en", pwp\->pw_name,
 199                pwp\->pw_uid, pwp\->pw_dir, pwp\->pw_shell);
 200     }
 201     endpwent();
 202     exit(EXIT_SUCCESS);
 203 }
 204 .fi
 205 .\" perhaps add error checking - should use strerror_r
 206 .\" #include <errno.h>
 207 .\" #include <stdlib.h>
 208 .\"         if (i) {
 209 .\"               if (i == ENOENT)
 210 .\"                     break;
 211 .\"               printf("getpwent_r: %s", strerror(i));
 212 .\"               exit(EXIT_SUCCESS);
 213 .\"         }
 214 .SH SEE ALSO
 215 .BR fgetpwent (3),
 216 .BR getpw (3),
 217 .BR getpwent (3),
 218 .BR getpwnam (3),
 219 .BR getpwuid (3),
 220 .BR putpwent (3),
 221 .BR passwd (5)