Using Subfiles to Minimize I/O Operations

You can use subfiles to read or write a number of records to and from a display in one operation.

Example:

The following subfile example uses DDS from T1520DDG and T1520DDH to display a list of names and telephone numbers.

To create the display file T1520DDG using the DDS source shown below, enter:

CRTDSPF FILE(MYLIB/T1520DDG) SRCFILE(QCPPLE/QADDSSRC)

Figure 1. T1520DDG — DDS Source for a Subfile Display

     A                                      DSPSIZ(24 80 *DS3)
     A          R SFL                       SFL
     A            NAME          10A  B 10 25
     A            PHONE         10A  B    +5
     A          R SFLCTL                    SFLCTL(SFL)
     A                                      SFLPAG(5)
     A                                      SFLSIZ(26)
     A                                      SFLDSP
     A                                      SFLDSPCTL
     A                                 22 25'<PAGE DOWN> FOR NEXT PAGE'
     A                                 23 25'<PAGE UP> FOR PREVIOUS PAGE'

To create the physical file T1520DDH using the DDS source shown below, enter:

CRTPF FILE(MYLIB/T1520DDH) SRCFILE(QCPPLE/QADDSSRC)


                R ENTRY
                  NAME          10A
                  PHONE         10A

Type the following data into T1520DDH:

David     435-5634
Florence  343-4537
Irene     255-5235
Carrie    747-5347
Michele   634-4557

To create the program T1520SUB using the source shown below, enter:

CRTBNDC PGM(MYLIB/T1520SUB) SRCFILE(QCPPLE/QACSRC)

/* This program illustrates how to use subfiles.                      */ 
#include <stdio.h>
#include <stdlib.h>
#include <recio.h> 
#define LEN          10
#define NUM_RECS     20
#define SUBFILENAME  "*LIBL/T1520DDG"
#define PFILENAME    "*LIBL/T1520DDH"
 
typedef struct{
    char name[LEN];
    char phone[LEN];
}pf_t; 
#define RECLEN sizeof(pf_t)
 
void init_subfile(_RFILE *, _RFILE *);

int main(void)
{
    _RFILE           *pf;
    _RFILE           *subf; 
/* Open the subfile and the physical file.                            */ 
    if ((pf = _Ropen(PFILENAME, "rr")) == NULL)
    {
        printf("can't open file %s\n", PFILENAME);
        exit(1);
    }
    if ((subf = _Ropen(SUBFILENAME, "ar+")) == NULL)
    {
        printf("can't open file %s\n", SUBFILENAME);
        exit(2);
    }
/* Initialize the subfile with records from the physical file.        */ 
    init_subfile(pf, subf);

 /* Write the subfile to the display by writing a record to the        */
/* subfile control format.                                            */
     _Rformat(subf, "SFLCTL");
     _Rwrite(subf, "", 0);
     _Rreadn(subf, "", 0, __DFT);
 
/* Close the physical file and the subfile.                           */ 
     _Rclose(pf);
     _Rclose(subf);
}
void init_subfile(_RFILE *pf, _RFILE *subf)
  {
        _RIOFB_T      *fb;
        int           i;
        pf_t          record;
 
/* Select the subfile record format.                                  */ 
        _Rformat(subf, "SFL"); 
        for (i = 1; i <= NUM_RECS; i++)
        {
               fb = _Rreadn(pf, &record, RECLEN, __DFT);
               if (fb->num_bytes != EOF)
               {
                 fb = _Rwrited(subf, &record, RECLEN, i);
                 if (fb->num_bytes != RECLEN)
                 {
                   printf("error occurred during write\n");
                   exit(3);
                 }
               }
        }
    }

This program uses _Ropen() to open subfile T1520DDG and physical file T1520DDH. The subfile is then initialized with records from the physical file. Subfile records are written to the display using the _Rwrited() function.

To run the program T1520SUB and see the output, enter:

CALL PGM(MYLIB/T1520SUB)



              David     435-5634
              Florence     343-4537
              Irene     255-5235
              Carrie     747-5347
              Michele     643-4557




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