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TMPFILE(3)               BSD 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 *s);

     char *
     tempnam(const char *dir, const char *pfx);

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+'.  If the environment variable TMPDIR is defined, the file is created in the specified direc-tory. directory.
     tory.  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 refer-ence reference
     ence an existing file at some indeterminate point in the past.  P_tmpdir is defined in the include file
     <stdio.h>.  If the argument s is non-NULL, the file name is copied to the buffer it references.  Other-wise, Otherwise,
     wise, the file name is copied to a static buffer.  In either case, tmpnam() returns a pointer to the
     file name.

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

     The argument pfx, 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 success, 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.

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 specified for the library function
     mktemp(3).

     The tempnam() function may fail and set errno for any of the errors specified 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 selec-tion selection
     tion of the file name and the creation of the file, which allows malicious users to potentially over-write overwrite
     write arbitrary files in the system, depending on the level of privilege of the running program.  Addi-tionally, Additionally,
     tionally, 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 the FSA.)

LEGACY DESCRIPTION
     In legacy mode, the order directories are tried by the tempnam() function is different; the environment
     variable TMPDIR (if defined) is used first.

SEE ALSO
     mkstemp(3), mktemp(3)

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

BSD                            November 12, 2008                           BSD