TMPFILE(3)                     Library Routines                     TMPFILE(3)




NAME

       tempnam, tmpfile, tmpnam - temporary file routines


SYNOPSIS

       #include <stdio.h>

       FILE * tmpfile(void);
       char * tmpnam(char *str);
       char * tempnam(const char *tmpdir, const char *prefix);


DESCRIPTION

       The  tmpfile  function  returns a pointer to a stream associated with a
       file descriptor returned by the routine mkstemp(3).  The  created  file
       is  unlinked  before  tmpfile returns, causing the file to be automati-
       cally deleted when the last reference to it is  closed.   The  file  is
       opened with the access value w+b.

       The  tmpnam  function returns a pointer to a file name, in the P_tmpdir
       directory, which did not reference an existing file at some  indetermi-
       nate  point  in  the  past.   P_tmpdir  is  defined in the include file
       stdio.h.  If the argument str is non-NULL, the file name is  copied  to
       the  buffer  it  references.   Otherwise,  the file name is copied to a
       static buffer.  In either case, tmpnam returns a pointer  to  the  file
       name.

       The  buffer referenced by str is expected to be at least L_tmpnam bytes
       in length.  L_tmpnam is defined in the include file stdio.h.

       The tempnam function is similar to tmpnam, but provides the ability  to
       specify  the  directory  which  will contain the temporary file and the
       file name prefix.

       The environment variable TMPDIR (if set), the  argument  dir  (if  non-
       NULL), the directory P_tmpdir, and the directory /tmp are tried, in the
       listed order, as directories in which to store the temporary file.

       The argument prefix, if non-NULL, is used to specify a file  name  pre-
       fix,  which  will  be the first part of the created file name.  Tempnam
       allocates memory in which to store the file name; the returned  pointer
       may be used as a subsequent argument to free(3).


RETURN VALUES

       The  tmpfile  function returns a pointer to an open file stream on suc-
       cess, and a NULL pointer on error.

       The tmpnam and tempfile functions return a pointer to a  file  name  on
       success, and a NULL pointer on error.


ERRORS

       The tmpfile function may fail and set the global variable errno for any
       of  the  errors  specified  for  the  library  functions  fdopen(3)  or
       mkstemp(3).

       The tmpnam function may fail and set errno for any of the errors speci-
       fied for the library function mktemp(3).

       The tempnam function may fail and set errno for any of the errors spec-
       ified for the library functions malloc(3) or mktemp (3).


SEE ALSO

       mkstemp(3), mktemp(3)


STANDARDS

       The tmpfile and tmpnam functions conform to ANSI C.


BUGS

       These interfaces are provided for System V and ANSI compatibility only.
       The mkstemp(3) interface is strongly preferred.

       There are four important problems with these  interfaces  (as  well  as
       with  the  historic  mktemp(3)  interface).  First, there is an obvious
       race between file name selection and file creation and deletion.   Sec-
       ond,  most  historic  implementations  provide only a limited number of
       possible temporary file names (usually 26) before file names will start
       being recycled.  Third, the System V implementations of these functions
       (and of mktemp) use the access(2) function to determine whether or  not
       the  temporary file may be created.  This has obvious ramifications for
       setuid or setgid programs,  complicating  the  portable  use  of  these
       interfaces in such programs.  Finally, there is no specification of the
       permissions with which the temporary files are created.

       This implementation does not have these flaws,  but  portable  software
       cannot depend on that.  In particular, the tmpfile interface should not
       be used in software expected to be used on other systems  if  there  is
       any  possibility  that  the user does not wish the temporary file to be
       publicly readable and writable.



GNO                            26 November 1995                     TMPFILE(3)

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