Accepting and Displaying Screen Section Items

ACCEPT and DISPLAY operations involving Screen Section items are treated like any other ACCEPT or DISPLAY operation, but with one important difference. Consider the following code:

 working-storage section.
 01 item-a              pic 9(5).
 01 item-b              pic 9(10).
 01 item-c              pic x(10).
 screen section.
 01 demo-screen.
     03 blank screen.
     03 line 1 column 1 pic z(4)9 from item-a.
     03 line 3 column 1 pic 9(10) to item-b.
     03 line 5 column 1 pic x(10) using item-c.

When this code is compiled, the Compiler sets up a work area for each Screen Section level-01 item (record). In this example, a work area is set up for demo-screen, large enough to hold the data for the three fields.

When the following statement is executed:

display demo-screen

the contents of item-a and item-c are moved from Working-Storage Section into the work area, then the data in the work area for these two fields is displayed on the screen. item-b is not displayed because it is an ACCEPT-only field.

When the following statement is executed:

accept demo-screen

data is accepted into the work area for item-b and item-c and then the data for these two fields is moved from the work area into the Working-Storage Section. Data is not accepted into item-a because it is a DISPLAY-only field.

It is important to note that moves from the Data Division to the work area occur only on execution of a DISPLAY statement, and moves from the work area to the Data Division occur only during execution of an ACCEPT statement. If two ACCEPT statements are executed one after another with no intervening DISPLAY statement, the initial contents of the fields at the start of the second ACCEPT are those which were put into the work area during the previous ACCEPT operation not the current contents of the Data Division items.

Another implication of this is that a field should not be defined as numeric-edited in both the Data Division and the Screen Section. This results in the compiler making numeric-edited to numeric-edited moves in order to move the Data Division item into the work area and back again. The action of such moves is undefined and has unpredictable results. This is the case even if both the Data Division item and the Screen Section item have the same picture.

For example, if the following lines are coded in your program:

working-storage section.
 01 ws-item     pic zz9.99 value 1.23
 screen section.
 01 demo-screen.
     03 pic zz9.99 using ws-item.
 procedure division.
     display demo-screen.

The result of the DISPLAY operation is undefined. The items used in the Data Division as source or target for Screen Section ACCEPT or DISPLAY statements should always be non-edited fields.