Processing Work Files and Nested Loops

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# Processing Work Files and Nested Loops

This document describes restrictions on the use of work file attributes, the support of work file formats and the impact of `READ` loops.

- Work File Format and Attributes

- Maximum File Transfer Record Length for Natural Connection

- Streaming

- Dynamic Variables in READ WORK FILE

- Nested READ Loops

- Subsequent READ Loops

## Work File Format and Attributes

Below are the restrictions that apply to the use of work file attributes:

- Accessing PC work files is restricted to a fixed record length of 1073741823 bytes or 32767 bytes when using the statement `WRITE WORK FILE VARIABLE`. Depending on the Entire Connection version installed on the PC, additional restrictions may apply as described below.

## Maximum File Transfer Record Length for Natural Connection

The maximum record length supported for file transfer depends on the version of Entire Connection installed on the PC.

For Entire Connection up to Version 4.2, the maximum record length is limited by the number of bytes that can be displayed on the appropriate 3270 model. For example, for a 3270 Model 2 device the record length is 24*80 = 1920 bytes. Since all data buffers are enclosed by a header and trailer, the resulting net record length is 1887 bytes.

For Entire Connection Version 4.3.1, the maximum record length is limited to 32 KB - 1 byte = 32767 bytes.

As of Entire Connection Version 4.3.2 Fix Level 1 and Entire Screen Builder Version 5.2.1, the maximum record length is increased to 1 GB - 1 byte = 1073741823 bytes. But writing work files in variable format (`WRITE WORK VARIABLE`) is still restricted to a maximum record length of 32 KB - 1 byte.

## Streaming

Entire Connection provides the option to transfer byte-streamed data that are non-record-oriented. A byte-streamed data transfer is activated when a `READ WORK FILE` or `WRITE WORK FILE` statement is coded with only one single operand of binary format.

### Downloading and Uploading Binary Data

Binary data is usually object code or executable code that does not contain displayable or printable characters. To prevent standard character translations being performed during data transfer, Natural and Entire Connection use special methods for transferring binary data.

To download binary data

1. Define a binary variable.

2. If the last block of downloaded data contains less data than the block size chosen, insert `X'FF'` at the position that marks the end of the binary data. (If you omit `X'FF'`, the rest of the last block will be filled with `X00`.)

To upload binary data

1. Define a binary variable.

2. Remove `X'FF` from the last block. `X'FF` marks the end of the binary data.

## Dynamic Variables in READ WORK FILE

If you define a dynamic variable of the format binary or alphanumeric as operand of a `READ WORK FILE` statement, when processing the corresponding `READ` loop, any resize operation on this variable will only be valid until the next `READ` is performed. While processing the `READ`, Natural resizes all dynamic variables to the size they had when the work file was opened. This is required in the open process which determines the record layout. The record layout is mandatory for processing the corresponding work file. The record layout is valid until the next close of the work file occurs.

Exception: An internal resize cannot be performed for inner loops if nested `READ` loops are processed on the same work file. See also the programming recommendations about nested loops below. If a dynamic variable of size 0 is used as the only operand of a `READ WORK FILE` statement, Natural issues the error NAT1500.

## Nested READ Loops

Do not specify nested `READ` loops on one work file. The result of the inner loop(s) can be unpredictable if the operands of the inner loop do not correspond to the operands of the outer loop. The reason is that all records uploaded from the PC are processed in the format that was determined when the work file was opened in the outermost loop.

Below are example programs that demonstrate the unpredictable results the inner loop(s) of nested `READ` loops can have.

- Example of Inner READ Loop

- Example of READ Loop and CALLNAT

### Example of Inner READ Loop

In the example program `PCNESTED`, during `READ` processing, another `READ` is performed:

    /* PCNESTED
    /*
    DEFINE DATA LOCAL
      1 #REC1   (A) DYNAMIC
      1 #NUMBER (N10)
    END-DEFINE
    *
    MOVE ALL 'TEST RECORD 1' TO #REC1 UNTIL 100
    READ WORK FILE 1 #REC1
       READ WORK FILE 1 #NUMBER
         DISPLAY #NUMBER
       END-WORK
    END-WORK
    END

### Example of READ Loop and CALLNAT

In the example program `PCMAIN` and subprogram `PCRSUB01`, during `READ` loop processing, an external object is called:

    /* PCMAIN
    /*
    DEFINE DATA
    LOCAL
      1 RECL (A2000)
      1 REDEFINE RECL
        2 RECNR (N4)
      1 CO   (N4
    END-DEFINE
    *
    WRITE WORK 1 COMMAND
     'SET PCFILE 2 UP DATA C:/TSTPCAM/PCMAIN.TXT'
    READ WORK 2 RECL
      DISPLAY RECL (AL=72)
      CALLNAT 'PCRSUB01' RECL
    END-WORK
    END

Subprogram `PCRSUB01`:

    /*Subprogram PCRSUB01
    /*
    DEFINE DATA
    PARAMETER
      1 RECL (A2000)
    LOCAL
      1 #CC1 (A20)
      1 #CC2 (N4)
    *
    END-DEFINE
    READ WORK 2 RECL
      #CC1 #CC2
      DISPLAY #CC1 #CC2
    END-WORK
    END

## Subsequent READ Loops

If a `READ` loop is terminated by a conditional `ESCAPE`, close the work file explicitly with the `CLOSE WORK FILE` statement so that the same work file can be processed in a subsequent `READ` in the same object.

Exception: You can omit the `CLOSE WORK FILE` if you need not read the file again from the beginning, and if the subsequent `READ` uses the same record layout as the preceding one.

Below is an example that demonstrates how to correctly code a program with two `READ` loops on one work file.

### Example of Loop with ESCAPE and CLOSE

In the example program `PCESCAPE`, the work file is explicitly closed after the first `READ` loop has been terminated by `ESCAPE BOTTOM` so that the second `READ` loop must reopen the work file:

    /*PCESCAPE
    /*
    DEFINE DATA
    LOCAL
      1 #CC1        (A20)
      1 #CC2        (A40)
      1 #COUNTER    (I2)
    *
    END-DEFINE
    READ WORK 2 #CC1
      DISPLAY #CC2
      ADD 1 TO #COUNTER
      IF #COUNTER GE 3
        ESCAPE BOTTOM
      END-IF
    END-WORK
    CLOSE WORK FILE 2
    *
    READ WORK 2 #CC2
      DISPLAY #CC2
    END-WORK
    END

### On this page

- Work File Format and Attributes
- Maximum File Transfer Record Length for Natural Connection
- Streaming
- Dynamic Variables in READ WORK FILE
- Nested READ Loops
- Subsequent READ Loops