tempnam(3)

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

6       tempnam - create a name for a temporary file
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <stdio.h>
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14       char *tempnam(const char *dir, const char *pfx);
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16   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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18       tempnam():
19           Since glibc 2.19:
20               _DEFAULT_SOURCE
21           glibc 2.19 and earlier:
22               _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

25       Never use this function.  Use mkstemp(3) or tmpfile(3) instead.
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27       The  tempnam()  function  returns a pointer to a string that is a valid
28       filename, and such that a file with this name did not exist when  temp‐
29       nam()  checked.   The  filename  suffix  of the pathname generated will
30       start with pfx in case pfx is a non-NULL string of at most five  bytes.
31       The  directory  prefix part of the pathname generated is required to be
32       "appropriate" (often that at least implies writable).
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34       Attempts to find an appropriate  directory  go  through  the  following
35       steps:
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37       a) In case the environment variable TMPDIR exists and contains the name
38          of an appropriate directory, that is used.
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40       b) Otherwise, if the dir argument is non-NULL and  appropriate,  it  is
41          used.
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43       c) Otherwise, P_tmpdir (as defined in <stdio.h>) is used when appropri‐
44          ate.
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46       d) Finally an implementation-defined directory may be used.
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48       The string returned by tempnam() is allocated using malloc(3) and hence
49       should be freed by free(3).
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RETURN VALUE

52       On success, the tempnam() function returns a pointer to a unique tempo‐
53       rary filename.  It returns NULL if a unique name cannot  be  generated,
54       with errno set to indicate the error.
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ERRORS

57       ENOMEM Allocation of storage failed.
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ATTRIBUTES

60       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
61       tributes(7).
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63       ┌────────────────────────────────────────┬───────────────┬─────────────┐
64       │Interface                               │ Attribute     │ Value       │
65       ├────────────────────────────────────────┼───────────────┼─────────────┤
66       │tempnam()                               │ Thread safety │ MT-Safe env │
67       └────────────────────────────────────────┴───────────────┴─────────────┘
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STANDARDS

70       POSIX.1-2008.
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HISTORY

73       SVr4, 4.3BSD, POSIX.1-2001.  Obsoleted in POSIX.1-2008.
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NOTES

76       Although tempnam() generates names that are difficult to guess,  it  is
77       nevertheless  possible  that  between the time that tempnam() returns a
78       pathname, and the time that the program opens it, another program might
79       create  that  pathname  using open(2), or create it as a symbolic link.
80       This can lead to security holes.  To avoid such possibilities, use  the
81       open(2)  O_EXCL  flag  to  open  the  pathname.   Or  better  yet,  use
82       mkstemp(3) or tmpfile(3).
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84       SUSv2 does not mention the use of TMPDIR; glibc will use it  only  when
85       the  program  is not set-user-ID.  On SVr4, the directory used under d)
86       is /tmp (and this is what glibc does).
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88       Because it dynamically allocates memory used to  return  the  pathname,
89       tempnam() is reentrant, and thus thread safe, unlike tmpnam(3).
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91       The  tempnam()  function  generates  a different string each time it is
92       called, up to TMP_MAX (defined in <stdio.h>) times.  If  it  is  called
93       more than TMP_MAX times, the behavior is implementation defined.
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95       tempnam() uses at most the first five bytes from pfx.
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97       The  glibc implementation of tempnam() fails with the error EEXIST upon
98       failure to find a unique name.
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BUGS

101       The precise meaning of "appropriate" is undefined;  it  is  unspecified
102       how accessibility of a directory is determined.
103