Special Uses for Group Fields

Because a group is treated as a single Format string, there are advantages to manipulating a group rather than its component fields. With care, you can achieve results that would not otherwise be possible. For example, group fields can be used to:

·    Access discrete portions (substrings) of other fields. For example, assume that you want to divide a four-byte binary number into four individual bytes (to access and manipulate each byte individually). You cannot define a substring field for the number because it is a numeric field, and APPX restricts substrings to alphanumeric fields. You can, however, define a one-byte numeric field with four occurrences, a group field for the four-byte field, and another group field for the one byte/four-occurrence field. You set the value of the one-byte/four-occurrence group field equal to the value in the four-byte group field. Once the numeric values are copied into the one-byte group field, you can manipulate an individual occurrence (equal to a single byte in the original binary number).

·    Simplify statements definition. By using a group, you can manipulate two or more fields with a single statement, rather than a statement for each field. You can even manipulate entire records with a single statement. For example, if you have two files with record structures that contain the same 15 fields, and you combine all 15 into a single group field, you can compare the values in any two records by comparing the values in their respective group fields. If you do not define a group, an IF, SET, or some other statement must be repeated 15 times, once for each field on the record.