This example enables disk write verification. It creates a file named "VERIFY.DAT" and writes the critical data to it. After this is done, it restores the original settings.

#define INCL_DOSFILEMGR          /* File Manager values */
#define INCL_DOSERRORS           /* DOS Error values    */
#include <os2.h>
#include <stdio.h>
#include <string.h>

int main(VOID) {
   UCHAR  uchFileName[20]  = "VERIFY.DAT",     /* Name of file to use      */
          uchFileData[10] = "SampleData";      /* Stuff to put in file     */
   HFILE  hfFileHandle   = 0L;                 /* Handle for user file     */
   BOOL32 fUserVerify    = 0;                  /* User Verify flag setting */
   ULONG  ulAction       = 0,                  /* Action done by DosOpen   */
          ulWritten      = 0;                  /* Number of bytes written  */
   APIRET rc             = NO_ERROR;           /* Return code              */

   rc = DosQueryVerify(&fUserVerify);     /* Get current setting of VERIFY */
   if (rc != NO_ERROR) {
     printf("DosQueryVerify error: return code = %u\n", rc);
     return 1;
   } else {
     printf ("Original setting of Verify=%s\n",(fUserVerify) ? "On" : "Off");
   } /* endif */

   rc = DosSetVerify(1);                  /* Set VERIFY=ON                 */
   if (rc != NO_ERROR) {
     printf("DosSetVerify error: return code = %u\n", rc);
     return 1;  }

   /* Open the file VERIFY.DAT for read/write.  Create it if necessary */

   rc = DosOpen(uchFileName, &hfFileHandle, &ulAction,
                10L, FILE_NORMAL,
                OPEN_ACTION_CREATE_IF_NEW | OPEN_ACTION_OPEN_IF_EXISTS,
                OPEN_SHARE_DENYNONE  | OPEN_ACCESS_READWRITE, 0L);

   if (rc != NO_ERROR) {
      printf("DosOpen error: return code = %u\n", rc);
      return 1; }

         /* Write critical data to the file */

   rc = DosWrite (hfFileHandle, (PVOID) uchFileData,
                  sizeof(uchFileData), &ulWritten);
   if (rc == NO_ERROR) {
      printf ("%u bytes written to file %s with Verify=On\n",
               ulWritten,uchFileName);
   }

   rc = DosSetVerify(fUserVerify);         /* Restore user's verify value */
   if (rc != NO_ERROR) {
     printf("DosSetVerify error: return code = %u\n", rc);
     return 1;
   }
   rc = DosClose(hfFileHandle);            /* Close the file              */

   return NO_ERROR;
}