Handling errors in joining and splitting strings

During the joining or splitting of strings, the pointer used by STRING or UNSTRING might fall outside the range of the receiving field. A potential overflow condition exists, but COBOL does not let the overflow happen.

About this task

Instead, the STRING or UNSTRING operation is not completed, the receiving field remains unchanged, and control passes to the next sequential statement. If you do not code the ON OVERFLOW phrase of the STRING or UNSTRING statement, you are not notified of the incomplete operation.

Consider the following statement:


String Item-1 space Item-2 delimited by Item-3
    into Item-4
    with pointer String-ptr
    on overflow
        Display "A string overflow occurred"
End-String

These are the data values before and after the statement is performed:

Data item	`PICTURE`	Value before	Value after
`Item-1`	`X(5)`	AAAAA	AAAAA
`Item-2`	`X(5)`	EEEAA	EEEAA
`Item-3`	`X(2)`	EA	EA
`Item-4`	`X(8)`	bbbbbbbb¹	bbbbbbbb¹
`String-ptr`	`9(2)`	0	0
1. The symbol b represents a blank space.

Because String-ptr has a value (0) that falls short of the receiving field, an overflow condition occurs and the STRING operation is not completed. (Overflow would also occur if String-ptr were greater than 9.) If ON OVERFLOW had not been specified, you would not be notified that the contents of Item-4 remained unchanged.