tempnam(3)

1TEMPNAM(3)                 Linux Programmer's Manual                TEMPNAM(3)
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NAME

6       tempnam - create a name for a temporary file
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SYNOPSIS

9       #include <stdio.h>
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11       char *tempnam(const char *dir, const char *pfx);
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13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15       tempnam(): _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

18       The  tempnam()  function  returns a pointer to a string that is a valid
19       filename, and such that a file with this name did not exist when  temp‐
20       nam()  checked.   The  filename  suffix  of the pathname generated will
21       start with pfx in case pfx is a non-NULL string of at most five  bytes.
22       The  directory  prefix part of the pathname generated is required to be
23       "appropriate" (often that at least implies writable).
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25       Attempts to find an appropriate  directory  go  through  the  following
26       steps:
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28       a) In case the environment variable TMPDIR exists and contains the name
29          of an appropriate directory, that is used.
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31       b) Otherwise, if the dir argument is non-NULL and  appropriate,  it  is
32          used.
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34       c) Otherwise, P_tmpdir (as defined in <stdio.h>) is used when appropri‐
35          ate.
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37       d) Finally an implementation-defined directory may be used.
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39       The string returned by tempnam() is allocated using malloc(3) and hence
40       should be freed by free(3).
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RETURN VALUE

43       On  succes, the tempnam() function returns a pointer to a unique tempo‐
44       rary filename.  It returns NULL if a unique name cannot  be  generated,
45       with errno set to indicate the cause of the error.
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ERRORS

48       ENOMEM Allocation of storage failed.
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CONFORMING TO

51       SVr4, 4.3BSD, POSIX.1-2001.  POSIX.1-2008 marks tempnam() as obsolete.
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NOTES

54       Although  tempnam()  generates names that are difficult to guess, it is
55       nevertheless possible that between the time that  tempnam()  returns  a
56       pathname, and the time that the program opens it, another program might
57       create that pathname using open(2), or create it as  a  symbolic  link.
58       This  can lead to security holes.  To avoid such possibilities, use the
59       open(2)  O_EXCL  flag  to  open  the  pathname.   Or  better  yet,  use
60       mkstemp(3) or tmpfile(3).
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62       SUSv2  does  not mention the use of TMPDIR; glibc will use it only when
63       the program is not set-user-ID.  On SVr4, the directory used  under  d)
64       is /tmp (and this is what glibc does).
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66       Because  it  dynamically  allocates memory used to return the pathname,
67       tempnam() is reentrant, and thus thread safe, unlike tmpnam(3).
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69       The tempnam() function generates a different string  each  time  it  is
70       called,  up  to  TMP_MAX (defined in <stdio.h>) times.  If it is called
71       more than TMP_MAX times, the behavior is implementation defined.
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73       tempnam() uses at most the first five bytes from pfx.
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75       The glibc implementation of tempnam() will fail with the  error  EEXIST
76       upon failure to find a unique name.
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BUGS

79       The  precise  meaning  of "appropriate" is undefined; it is unspecified
80       how accessibility of a directory is determined.
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82       Never use this function.  Use mkstemp(3) or tmpfile(3) instead.
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COLOPHON

88       This page is part of release 3.53 of the Linux  man-pages  project.   A
89       description  of  the project, and information about reporting bugs, can
90       be found at http://www.kernel.org/doc/man-pages/.
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94                                  2013-04-19                        TEMPNAM(3)