Basic PDS 7.10 Call to C Routine to Open > 15 Files Fails (71795)

MORE INFORMATION

The failure occurs because the C file-open routines check the run-time variable _nfile to see if there are enough file handles available to open the file.

You can modify the C 6.00 run time to support more than 15 files, as described in the C 6.00 documentation; however, if you link a C 6.00 routine with Microsoft Basic PDS 7.10, the modified portion of the run time will not get incorporated into the actual executable program (the Basic run-time code is used instead).

Increasing the file handle count by calling interrupt 21 Hex with function 67 Hex in Basic does not resolve the problem because this method does not change the run-time variable that C 6.00 is checking (_nfile) to indicate the new number of available file handles.

The following method to work around the problem directly modifies the run-time variable _nfile from the C 6.00 function that is called from Basic PDS 7.10. This workaround is based on internal details of the C and Basic run-time routines, and is not guaranteed to work for versions other than those specified above. If you chose to use this workaround, be certain that the call to interrupt 21 Hex with function 67 Hex (to increase the available file handles) has been done and returned successfully before calling the C function that modifies _nfile.

Compile and link the workaround programs as follows:

   BC /o test ;
   CL /c /AM files.c ;
   LINK test files,,,BCL71ENR MLIBCE QBX /NOE /NOD ;
				

TEST.BAS

'$INCLUDE: 'QBX.BI'
DECLARE SUB profile CDECL ()
DIM InRegs AS RegType, OutRegs AS RegType
CLS
InRegs.ax = &H6700
InRegs.bx = 40
CALL Interrupt(&H21, InRegs, OutRegs)  'Increases MS-DOS file handles.
CALL profile   ' Calls the C routine.
PRINT "In Basic again."
END
				

FILES.C

#define SYSCALL 0x21
#include <stdio.h>
#include <conio.h>
#include <io.h>
#include <dos.h>
#include <bios.h>
#include <fcntl.h>
#include <sys\types.h>
#include <sys\stat.h>
#include <sys\locking.h>
#include <share.h>
#include <stdlib.h>

union REGS regs;
extern int _nfile;                  /* run-time variable */ 
void extern profile(void);

void extern profile(void)
 {
   int i,handle[20];
   char filename[20][20];

   _nfile = 40;

   strcpy(filename[0],"t1.tmp\0");   strcpy(filename[1],"t2.tmp\0");
   strcpy(filename[2],"t3.tmp\0");   strcpy(filename[3],"t4.tmp\0");
   strcpy(filename[4],"t5.tmp\0");   strcpy(filename[5],"t6.tmp\0");
   strcpy(filename[6],"t7.tmp\0");   strcpy(filename[7],"t8.tmp\0");
   strcpy(filename[8],"t9.tmp\0");   strcpy(filename[9],"t10.tmp\0");
   strcpy(filename[10],"t11.tmp\0"); strcpy(filename[11],"t12.tmp\0");
   strcpy(filename[12],"t13.tmp\0"); strcpy(filename[13],"t14.tmp\0");
   strcpy(filename[14],"t15.tmp\0"); strcpy(filename[15],"t16.tmp\0");
   strcpy(filename[16],"t17.tmp\0"); strcpy(filename[17],"t18.tmp\0");
   strcpy(filename[18],"t19.tmp\0"); strcpy(filename[19],"t20.tmp\0");

   for (i=0;i<20;i++)
      {
        handle[i] = sopen(filename[i], O_BINARY | O_RDWR | O_CREAT,
                          SH_DENYNO, S_IREAD | S_IWRITE);
        if( handle[i] == -1 )
            printf( "Can't open file %d\n",i );
        else
            printf( "Opened file %d!\n",i);
      }
  printf("end of C, going back to Basic \n");
}