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       The  tempnam()  function  returns a pointer to a unique temporary file‐
44       name, or NULL if a unique name cannot be generated.
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ERRORS

47       ENOMEM Allocation of storage failed.
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CONFORMING TO

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

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

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

87       This  page  is  part of release 3.25 of the Linux man-pages project.  A
88       description of the project, and information about reporting  bugs,  can
89       be found at http://www.kernel.org/doc/man-pages/.
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93                                  2008-08-06                        TEMPNAM(3)