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Flash name of exe com file that is being opened in write mode

Flash name of exe com file that is being opened in write mode

#pragma inline
#include <dos.h>
#include<bios.h>
void interrupt(*old_21)();
void interrupt new_21(unsigned BP_21, unsigned DI_21, unsigned SI_21,
unsigned DS_21, unsigned ES_21, unsigned DX_21, unsigned CX_21,
unsigned BX_21, unsigned AX_21, unsigned IP_21, unsigned CS_21,
unsigned flags_21);
char far *scr = (char far *)0xb8000000;
int k = 2000, i = 0,j;
char filename[50], ch, op[50], *ptr = "open is";
char far *fname;
void main()
{
   old_21 = getvect(0x21);
   setvect(0x21, new_21);
   keep(0, 1000);
}

void interrupt new_21(unsigned BP_21, unsigned DI_21, unsigned SI_21,
unsigned DS_21, unsigned ES_21, unsigned DX_21, unsigned CX_21,
unsigned BX_21, unsigned AX_21, unsigned IP_21, unsigned CS_21,
unsigned flags_21)
{

   if(_AH == 0x4b)
   {
      fname = MK_FP(DS_21, DX_21);
      i = 0;
      while(*fname)
      {
         ch = *fname;
         op[i] = ch;
         fname++;
         i++;
      }
      op[i] = 0;
   }
   if(_AH == 0x3d || _AH == 0x3c)
   {
      fname = MK_FP(DS_21, DX_21);
      i = 0;
      while(*fname)
      {
         ch = *fname;
         filename[i] = ch;
         fname++;
         i++;
      }
      filename[i] = 0;
      strupr(filename);
      i = 0;
      while(filename[i] != '.' && filename[i])
      {
         i++;
      }
      if((!strcmp(&filename[i+1], "EXE")) || (!strcmp(&filename[i+1], "SYS"))
      || (!strcmp(&filename[i+1], "COM")))
      {
         //*(scr + 1000) = 'P';
         //   scr = ptr;
         if(AX_21 & 3)
         {

      //fwrite(39, 1, 1, "file opened is:- ");
      //   fwrite(58, 1, 1, "      ");
      //fwrite(58, 1, 1, op);
      //printf("%sname is",op);
            for(j = 0; op[j]; j++)
            {
               *(scr + k + j * 2) = op[j];
            }
            k = k + j * 2 + 8;
            for(j = 0; filename[j]; j++)
            {
               *(scr + k + j * 2) = filename[j];
            }
            k = k + j * 2;
            while((ch = bioskey(0)) != 'y' &&  ch != 'n')
            if(ch == 'n')
            {
               asm stc;
               asm pushf;
               asm pop flags_21;
               return;
            }
         }
      }
   }
   asm pop bp;
   asm pop di;
   asm pop si;
   asm pop ds;
   asm pop es;
   asm pop dx;
   asm pop cx;
   asm pop bx;
   asm pop ax;
   asm jmp cs:_old_21;
}