BUG: DOSGetCurDate Incorrect in DISKMENU PWB Extension

The information in this article applies to:

• Microsoft Programmer's WorkBench for MS-DOS, versions 2.0 and 2.01.49

SYMPTOMS

An attempt to use the DOSGetCurDate function in the DISKMENU.C sample Programmer's WorkBench (PWB) extension provided with Microsoft C/C++ version 7.0 fails to return the date correctly.

CAUSE

The DOSGetCurDate function is designed to return the date in a packed MS- DOS format. This format is used by Interrupt 21h Function 57h that the DOSSetFileTime function calls. Therefore, the format of the unsigned integer result value should be as follows:

    bits 00h-04h   = day   (1-31)
    bits 05h-08h   = month (1-12)
    bits 09h-0Fh   = year  (relative to 1980)

RESOLUTION

Replace the DOSGetCurDate function in the DISKMENU extension with the following code:

   //  DOSGetCurDate - Get current DOS date
   //
   //  Returns the current DOS date in packed format
   //
   unsigned __pascal DOSGetCurDate(void)
   {
      unsigned rv;
      _asm
      {
         mov ah, 2ah         // Get the date
         int 21h
         sub cx, 1980        // CX contains the year. Make relative
                             // to 1980 for DOSSetFileTime function
      #ifdef _M_I8086
         shl cx, 1           // shift to add month from DH
         shl cx, 1
         shl cx, 1
         shl cx, 1
      #else
         shl cx, 4
      #endif
         or  cl, dh           // insert month from DH
      #ifdef _M_I8086
         shl cx, 1            // shift to add day
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
      #else
         shl cx, 5
      #endif
         or  cl, dl           // insert day from DL
         mov rv, cx
      }
      return rv;
   }

MORE INFORMATION

The incorrect code is as follows:

Sample code

   unsigned __pascal DOSGetCurDate( void )
   {
      unsigned rv;
      _asm
      {
         mov ah, 2ah
         int 21h
         sub cx, 1980
      #ifdef _M_I8086
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
         shl cx, 1
      #else
         shl cx, 9
      #endif
         or  cl, dl
      #ifdef _M_I8086
         shl dh, 1
         shl dh, 1
         shl dh, 1
         shl dh, 1
         shl dh, 1
      #else
         shl dh, 5
      #endif
         or  cl, dh
         mov rv, cx
      }
      return rv;
   }