getpwent_r(3)

1getpwent_r(3)              Library Functions Manual              getpwent_r(3)
2
3
4

NAME

6       getpwent_r, fgetpwent_r - get passwd file entry reentrantly
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <pwd.h>
13
14       int getpwent_r(struct passwd *restrict pwbuf,
15                      char buf[restrict .buflen], size_t buflen,
16                      struct passwd **restrict pwbufp);
17       int fgetpwent_r(FILE *restrict stream, struct passwd *restrict pwbuf,
18                      char buf[restrict .buflen], size_t buflen,
19                      struct passwd **restrict pwbufp);
20
21   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22
23       getpwent_r(),
24           Since glibc 2.19:
25               _DEFAULT_SOURCE
26           glibc 2.19 and earlier:
27               _BSD_SOURCE || _SVID_SOURCE
28
29       fgetpwent_r():
30           Since glibc 2.19:
31               _DEFAULT_SOURCE
32           glibc 2.19 and earlier:
33               _SVID_SOURCE
34

DESCRIPTION

36       The functions getpwent_r() and fgetpwent_r() are the reentrant versions
37       of getpwent(3) and fgetpwent(3).  The former reads the next passwd  en‐
38       try  from  the stream initialized by setpwent(3).  The latter reads the
39       next passwd entry from stream.
40
41       The passwd structure is defined in <pwd.h> as follows:
42
43           struct passwd {
44               char    *pw_name;      /* username */
45               char    *pw_passwd;    /* user password */
46               uid_t    pw_uid;       /* user ID */
47               gid_t    pw_gid;       /* group ID */
48               char    *pw_gecos;     /* user information */
49               char    *pw_dir;       /* home directory */
50               char    *pw_shell;     /* shell program */
51           };
52
53       For more information about the fields of this structure, see passwd(5).
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55       The nonreentrant functions return a pointer to  static  storage,  where
56       this  static  storage contains further pointers to user name, password,
57       gecos field, home directory and shell.   The  reentrant  functions  de‐
58       scribed  here  return all of that in caller-provided buffers.  First of
59       all there is the buffer pwbuf that can hold a struct passwd.  And  next
60       the  buffer  buf  of size buflen that can hold additional strings.  The
61       result of these functions, the struct passwd read from the  stream,  is
62       stored  in  the  provided  buffer  *pwbuf, and a pointer to this struct
63       passwd is returned in *pwbufp.
64

RETURN VALUE

66       On success, these functions return 0 and *pwbufp is a  pointer  to  the
67       struct  passwd.   On  error,  these functions return an error value and
68       *pwbufp is NULL.
69

ERRORS

71       ENOENT No more entries.
72
73       ERANGE Insufficient buffer space supplied.  Try again with larger  buf‐
74              fer.
75

ATTRIBUTES

77       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
78       tributes(7).
79
80       ┌──────────────┬───────────────┬───────────────────────────────────────┐
81       │Interface     │ Attribute     │ Value                                 │
82       ├──────────────┼───────────────┼───────────────────────────────────────┤
83       │getpwent_r()  │ Thread safety │ MT-Unsafe race:pwent locale           │
84       ├──────────────┼───────────────┼───────────────────────────────────────┤
85       │fgetpwent_r() │ Thread safety │ MT-Safe                               │
86       └──────────────┴───────────────┴───────────────────────────────────────┘
87       In the above table, pwent in race:pwent signifies that if  any  of  the
88       functions  setpwent(), getpwent(), endpwent(), or getpwent_r() are used
89       in parallel in different threads of a program, then  data  races  could
90       occur.
91

VERSIONS

93       Other systems use the prototype
94
95           struct passwd *
96           getpwent_r(struct passwd *pwd, char *buf, int buflen);
97
98       or, better,
99
100           int
101           getpwent_r(struct passwd *pwd, char *buf, int buflen,
102                      FILE **pw_fp);
103

STANDARDS

105       None.
106

HISTORY

108       These  functions  are  done  in a style resembling the POSIX version of
109       functions like getpwnam_r(3).
110

NOTES

112       The function getpwent_r() is not really reentrant since it  shares  the
113       reading position in the stream with all other threads.
114

EXAMPLES

116       #define _GNU_SOURCE
117       #include <pwd.h>
118       #include <stdint.h>
119       #include <stdio.h>
120       #include <stdlib.h>
121
122       #define BUFLEN 4096
123
124       int
125       main(void)
126       {
127           struct passwd pw;
128           struct passwd *pwp;
129           char buf[BUFLEN];
130           int i;
131
132           setpwent();
133           while (1) {
134               i = getpwent_r(&pw, buf, sizeof(buf), &pwp);
135               if (i)
136                   break;
137               printf("%s (%jd)\tHOME %s\tSHELL %s\n", pwp->pw_name,
138                      (intmax_t) pwp->pw_uid, pwp->pw_dir, pwp->pw_shell);
139           }
140           endpwent();
141           exit(EXIT_SUCCESS);
142       }
143