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TMPFILE(3)            DragonFly Library Functions Manual            TMPFILE(3)


NAME

     tempnam, tmpfile, tmpnam -- temporary file routines


LIBRARY

     Standard C Library (libc, -lc)


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 automatically
     deleted when the last reference to it is closed.  The file is opened with
     the access value `w+'.  The file is created in the directory determined
     by the environment variable TMPDIR if set.  The default location if
     TMPDIR is not set is /tmp.

     The tmpnam() function returns a pointer to a file name, in the P_tmpdir
     directory, which did not reference an existing file at some indeterminate
     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 tmpdir (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 prefix,
     which will be the first part of the created file name.  The tempnam()
     function 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 tempnam() functions return a pointer to a file name on
     success, and a NULL pointer on error.


ENVIRONMENT

     TMPDIR  [tempnam() only] If set, the directory in which the temporary
             file is stored.  TMPDIR is ignored for processes for which
             issetugid(2) is true.


COMPATIBILITY

     These interfaces are provided from System V and ANSI compatibility only.

     Most historic implementations of these functions provide only a limited
     number of possible temporary file names (usually 26) before file names
     will start being recycled.  System V implementations of these functions
     (and of mktemp(3)) use the access(2) system call 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.

     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.


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).


SECURITY CONSIDERATIONS

     The tmpnam() and tempnam() functions are susceptible to a race condition
     occurring between the selection of the file name and the creation of the
     file, which allows malicious users to potentially overwrite arbitrary
     files in the system, depending on the level of privilege of the running
     program.  Additionally, there is no means by which file permissions may
     be specified.  It is strongly suggested that mkstemp(3) be used in place
     of these functions.


SEE ALSO

     mkstemp(3), mktemp(3)


STANDARDS

     The tmpfile() and tmpnam() functions conform to ISO/IEC 9899:1990
     (``ISO C90'').

DragonFly 3.5                   March 18, 2007                   DragonFly 3.5

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