mkstemp(3)

1mkstemp(3)                 Library Functions Manual                 mkstemp(3)
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NAME

6       mkstemp, mkostemp, mkstemps, mkostemps - create a unique temporary file
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <stdlib.h>
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14       int mkstemp(char *template);
15       int mkostemp(char *template, int flags);
16       int mkstemps(char *template, int suffixlen);
17       int mkostemps(char *template, int suffixlen, int flags);
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19   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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21       mkstemp():
22           _XOPEN_SOURCE >= 500
23               || /* glibc >= 2.12: */ _POSIX_C_SOURCE >= 200809L
24               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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26       mkostemp():
27           _GNU_SOURCE
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29       mkstemps():
30           /* glibc >= 2.19: */ _DEFAULT_SOURCE
31               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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33       mkostemps():
34           _GNU_SOURCE
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DESCRIPTION

37       The  mkstemp() function generates a unique temporary filename from tem‐
38       plate, creates and opens the file, and returns an open file  descriptor
39       for the file.
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41       The  last six characters of template must be "XXXXXX" and these are re‐
42       placed with a string that makes the filename unique.  Since it will  be
43       modified,  template  must  not  be a string constant, but should be de‐
44       clared as a character array.
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46       The file is created with permissions 0600, that is, read plus write for
47       owner  only.  The returned file descriptor provides both read and write
48       access to the file.  The file is opened with the open(2)  O_EXCL  flag,
49       guaranteeing that the caller is the process that creates the file.
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51       The mkostemp() function is like mkstemp(), with the difference that the
52       following bits—with the same meaning as for open(2)—may be specified in
53       flags:  O_APPEND,  O_CLOEXEC,  and O_SYNC.  Note that when creating the
54       file, mkostemp() includes the values O_RDWR, O_CREAT, and O_EXCL in the
55       flags  argument  given  to open(2); including these values in the flags
56       argument given to mkostemp() is unnecessary,  and  produces  errors  on
57       some systems.
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59       The  mkstemps()  function  is like mkstemp(), except that the string in
60       template contains a suffix of suffixlen characters.  Thus, template  is
61       of  the  form  prefixXXXXXXsuffix, and the string XXXXXX is modified as
62       for mkstemp().
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64       The mkostemps() function is to  mkstemps()  as  mkostemp()  is  to  mk‐
65       stemp().
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RETURN VALUE

68       On success, these functions return the file descriptor of the temporary
69       file.  On error, -1 is returned, and errno is set to indicate  the  er‐
70       ror.
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ERRORS

73       EEXIST Could  not create a unique temporary filename.  Now the contents
74              of template are undefined.
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76       EINVAL For mkstemp() and mkostemp(): The last six  characters  of  tem‐
77              plate were not XXXXXX; now template is unchanged.
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79              For  mkstemps() and mkostemps(): template is less than (6 + suf‐
80              fixlen) characters long, or the last  6  characters  before  the
81              suffix in template were not XXXXXX.
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83       These  functions  may  also  fail  with any of the errors described for
84       open(2).
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ATTRIBUTES

87       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
88       tributes(7).
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90       ┌────────────────────────────────────────────┬───────────────┬─────────┐
91       │Interface                                   │ Attribute     │ Value   │
92       ├────────────────────────────────────────────┼───────────────┼─────────┤
93       │mkstemp(), mkostemp(), mkstemps(),          │ Thread safety │ MT-Safe │
94       │mkostemps()                                 │               │         │
95       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

98       mkstemp()
99              POSIX.1-2001.
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101       mkstemps()
102              BSD.
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104       mkostemp()
105       mkostemps()
106              GNU.
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HISTORY

109       mkstemp()
110              4.3BSD, POSIX.1-2001.
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112       mkstemps()
113              glibc 2.11.  BSD, Mac OS X, Solaris, Tru64.
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115       mkostemp()
116              glibc 2.7.
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118       mkostemps()
119              glibc 2.11.
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121       In glibc versions 2.06 and earlier, the file is  created  with  permis‐
122       sions  0666,  that is, read and write for all users.  This old behavior
123       may be a security risk, especially since other UNIX flavors  use  0600,
124       and   somebody  might  overlook  this  detail  when  porting  programs.
125       POSIX.1-2008 adds a requirement that the  file  be  created  with  mode
126       0600.
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128       More  generally, the POSIX specification of mkstemp() does not say any‐
129       thing about file modes, so the application should make  sure  its  file
130       mode  creation  mask (see umask(2)) is set appropriately before calling
131       mkstemp() (and mkostemp()).
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