COBOL data (except key data) that is illegal by database standards is stored in the database as null unless you specifically override this default. (Use the ACUCOBOL-GT runtime configuration file variable 4GL_ILLEGAL_DATA to override.)
The following COBOL data usages are considered illegal by the database:
| Illegal Values | |
| USAGE DISPLAY numbers | LOW-VALUES , HIGH-VALUES, and SPACES |
| COMP-2 numbers | HIGH-VALUES and SPACES |
| COMP-3 numbers | HIGH-VALUES |
All other numeric types fit one of the preceding cases (depending on their internal storage format)
| DATE fields | The value "zero" and any other illegal conditions as defined by the date's USAGE type (see above) |
| text fields | LOW-VALUES |
BINARY numbers are always legal, and all values are legal in BINARY text fields.