windows-nt/Source/XPSP1/NT/base/crts/crtw32/lowio/mktemp.c

/***
*mktemp.c - create a unique file name
*
*       Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines _mktemp() - create a unique file name
*
*Revision History:
*       06-02-86  JMB   eliminated unneccesary routine exits
*       05-26-87  JCR   fixed bug where mktemp was incorrectly modifying
*                       the errno value.
*       12-11-87  JCR   Added "_LOAD_DS" to declaration
*       07-11-88  JCR   Optimized REG allocation
*       03-12-90  GJF   Replaced _LOAD_DS with _CALLTYPE1, added #include
*                       <cruntime.h>, removed #include <register.h> and
*                       fixed the copyright. Also, cleaned up the formatting
*                       a bit.
*       04-04-90  GJF   Added #include <process.h> and #include <io.h>. Removed
*                       #include <sizeptr.h>.
*       07-23-90  SBM   Replaced <assertm.h> by <assert.h>
*       08-13-90  SBM   Compiles cleanly with -W3
*       09-28-90  GJF   New-style function declarator.
*       01-16-91  GJF   ANSI naming.
*       11-30-92  KRS   Ported _MBCS code from 16-bit tree.
*       06-18-93  KRS   MBCS-only bug fix ported from 16-bit tree.
*       08-03-93  KRS   Call _ismbstrail instead of isdbcscode.
*       11-01-93  CFW   Enable Unicode variant.
*       02-21-94  SKS   Use ThreadID instead of ProcessID in multi-thread libs.
*       04-11-94  CFW   Fix first X handling, cycle 'a'-'z'.
*       02-06-95  CFW   assert -> _ASSERTE.
*       02-15-95  GJF   Appended Mac version of source file (somewhat cleaned
*                       up), with appropriate #ifdef-s.
*       03-28-96  GJF   Detab-ed. Also, replaced isdbcscode with __isdbcscode.
*       07-08-96  GJF   Replaced defined(_WIN32) with !defined(_MAC), and
*                       defined(_M_M68K) || defined(_M_MPPC) with 
*                       defined(_MAC). Removed obsolete REG* macros. Also, 
*                       cleaned up the format a bit.
*       05-17-99  PML   Remove all Macintosh support.
*
*******************************************************************************/

#include <cruntime.h>
#include <stdio.h>
#include <io.h>
#include <process.h>
#include <errno.h>
#include <dbgint.h>
#include <stddef.h>
#ifdef  _MBCS
#include <mbctype.h>
#include <mbdata.h>
#endif
#include <tchar.h>

/***
*_TSCHAR *_mktemp(template) - create a unique file name
*
*Purpose:
*       given a template of the form "fnamXXXXXX", insert number on end
*       of template, insert unique letter if needed until unique filename
*       found or run out of letters.  The number is generated from the Win32
*       Process ID for single-thread libraries, or the Win32 Thread ID for
*       multi-thread libraries.
*
*Entry:
*       _TSCHAR *template - template of form "fnamXXXXXX"
*
*Exit:
*       return pointer to modifed template
*       returns NULL if template malformed or no more unique names
*
*Exceptions:
*
*******************************************************************************/

_TSCHAR * __cdecl _tmktemp (
        _TSCHAR *template
        )
{
        _TSCHAR *string = template;
        unsigned number;
        int letter = _T('a');
        int xcount = 0;
        int olderrno;

        _ASSERTE(template != NULL);
        _ASSERTE(*template != _T('\0'));

        /*
         * The Process ID is not a good choice in multi-threaded programs
         * because of the likelihood that two threads might call mktemp()
         * almost simultaneously, thus getting the same temporary name.
         * Instead, the Win32 Thread ID is used, because it is unique across
         * all threads in all processes currently running.
         *
         * Note, however, that unlike *NIX process IDs, which are not re-used
         * until all values up to 32K have been used, Win32 process IDs are
         * re-used and tend to always be relatively small numbers.  Same for
         * thread IDs.
         */
#ifdef  _MT
        number = __threadid();
#else
        number = _getpid();
#endif

        while (*string)
                string++;

        /* replace last five X's */
#ifdef  _MBCS
        while ((--string>=template) && (!_ismbstrail(template,string))
                && (*string == 'X') && xcount < 5)
#else
        while (*--string == _T('X') && xcount < 5)
#endif
        {
                xcount++;
                *string = (_TSCHAR)((number % 10) + '0');
                number /= 10;
        }

        /* too few X's ? */
        if (*string != _T('X') || xcount < 5)
                return(NULL);

        /* set first X */
        *string = letter++;

        olderrno = errno;       /* save current errno */
        errno = 0;              /* make sure errno isn't EACCESS */

        /* check all the files 'a'-'z' */
        while ((_taccess(template,0) == 0) || (errno == EACCES))
        /* while file exists */
        {
                errno = 0;
                if (letter == _T('z') + 1) {
                        errno = olderrno;
                        return(NULL);
                }

                *string = (_TSCHAR)letter++;
        }

        errno = olderrno;
        return(template);
}