This example defines and adjust the maximum number of file handles.

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

int main(VOID){

  ULONG    CurMaxFH      = 0;          /* Current count of handles         */
  LONG     ReqCount      = 0;          /* Number to adjust file handles    */
  APIRET   rc            = NO_ERROR;   /* Return code                      */

  rc = DosSetRelMaxFH(&ReqCount,     /* Using 0 here will return the       */
                      &CurMaxFH);    /* current number of file handles     */

  if (rc != NO_ERROR) {
     printf("DosSetRelMaxFH error: return code = %u\n", rc);
     return 1;
  } else {
     printf("Maximum number of file handles is %u.\n", CurMaxFH);
  }

  rc = DosSetMaxFH(110L);            /* Set maximum file handles to 110  */

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

  ReqCount = -5L;                    /* Want 5 less file handles         */

  rc = DosSetRelMaxFH(&ReqCount,&CurMaxFH);     /* Change handle maximum */

  if (rc != NO_ERROR) {
     printf("DosSetRelMaxFH error: return code = %u\n", rc);
     return 1;
  } else {
     printf("Maximum number of file handles is now %u.\n", CurMaxFH);
  }

  return NO_ERROR;
}