Originální popis anglicky: 
mkstemp - make a unique filename
Návod, kniha: POSIX Programmer's Manual
#include <stdlib.h>
 
 
int mkstemp(char * 
template);  
 
The 
mkstemp() function shall replace the contents of the string pointed
  to by 
template by a unique filename, and return a file descriptor for
  the file open for reading and writing. The function thus prevents any possible
  race condition between testing whether the file exists and opening it for use.
  The string in 
template should look like a filename with six trailing
  
'X' s; 
mkstemp() replaces each 
'X' with a character from
  the portable filename character set. The characters are chosen such that the
  resulting name does not duplicate the name of an existing file at the time of
  a call to 
mkstemp().
Upon successful completion, 
mkstemp() shall return an open file
  descriptor. Otherwise, -1 shall be returned if no suitable file could be
  created.
No errors are defined.
The following sections are informative.
The following example creates a file with a 10-character name beginning with the
  characters 
"file" and opens the file for reading and writing.
  The value returned as the value of 
fd is a file descriptor that
  identifies the file.
 
#include <stdlib.h>
...
char template[] = "/tmp/fileXXXXXX";
int fd;
 
fd = mkstemp(template);
 
It is possible to run out of letters.
The 
mkstemp() function need not check to determine whether the filename
  part of 
template exceeds the maximum allowable filename length.
None.
None.
getpid() , 
open() , 
tmpfile() , 
tmpnam() , the Base
  Definitions volume of IEEE Std 1003.1-2001,
  
<stdlib.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
  Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
  Operating System Interface (POSIX), The Open Group Base Specifications Issue
  6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
  Engineers, Inc and The Open Group. In the event of any discrepancy between
  this version and the original IEEE and The Open Group Standard, the original
  IEEE and The Open Group Standard is the referee document. The original
  Standard can be obtained online at http://www.opengroup.org/unix/online.html
  .