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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DESCRIPTION

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

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

43       ENOMEM Allocation of storage failed.
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NOTES

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

71       The precise meaning of `appropriate' is undefined;  it  is  unspecified
72       how accessibility of a directory is determined.
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74       Never use this function. Use mkstemp(3) or tmpfile(3) instead.
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CONFORMING TO

77       SVr4, 4.3BSD, POSIX.1-2001
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