April 2006 Technical Tip – COBOL: Did you remember to test for numerics?
When performing data validation on zoned decimal numeric fields in COBOL, always check for NUMERIC. Never rely upon IFs and 88s alone! This article will demonstrate why.
I love 88s (condition names.) I often tell my students that I find them to be one of the nicest features in COBOL. But IF statements, with or without 88s, when performed on zoned decimal numeric fields, disregard the sign bits of all but the last digit. Consequently, it is possible to have a non-numeric character, such as any letter of the alphabet, in a supposed numeric field, and that field be treated as a number. IFs and 88s won’t catch the error. However, at least to my knowledge, COBOL’s check for NUMERIC cannot be fooled. Consider the following example
The reason for this is that C’13E79’ is equivalent to X’F1F3C5F7F9’ and when COBOL’s IF looks at a zoned decimal field, it ignores the zone bits (X’F’ and X’C’) in all but the rightmost byte. Indeed, the COBOL compiler will generate a machine level PACK instruction for the purpose of the compare (since zoned decimal instructions do not exist at the machine level) and this value packs to X’13579F’, which is a valid packed decimal numeric field.
So you should never rely upon a range check alone (with or without an 88.) The data could be properly checked as follows: IF INPUT-FLD-AS-9 IS NUMERIC AND VALID-VALUES
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