Informix Error -688

Reasons / Common Causes

-688 fires when a variable used in a context requiring a character type is declared as something else — per the official guidance, the fix is simply to correct the declaration to CHAR/ VARCHAR.

1. A variable declared as a non-character type (INTEGER, DATE, etc.) used somewhere that specifically requires CHAR/VARCHAR — for example, as the target of SET DEBUG FILE TO (per -649) or another character-specific context.
2. A variable reused from elsewhere in the routine (declared for a different, non-character purpose) repurposed for a character-specific use without redeclaring it.

Solutions / Resolution

1. Correct the declaration to CHAR/VARCHAR, per the official guidance, matching the width the specific context needs.
2. If the variable genuinely needs to hold both a non-character value and a character representation of it, declare a separate CHAR/VARCHAR variable for the character-specific use rather than trying to reuse the original.

Examples

The disallowed declaration

DEFINE v_debug_path INT;
SET DEBUG FILE TO v_debug_path;
-- -688: v_debug_path must be CHAR or VARCHAR

Corrected

DEFINE v_debug_path VARCHAR(200);
LET v_debug_path = '/path/to/debug/directory/routine_trace.out';
SET DEBUG FILE TO v_debug_path;

Diagnostic Checks

1. Identify the specific variable-name named in the error and the context it's used in, then correct its declaration to CHAR/VARCHAR with an appropriate width.

Related Errors / Related Topics

• -666 — "Variable variable-name must be declared INTEGER or SMALLINT." The mirror-image type requirement, for a different context (a ranged FOR loop variable) that needs a numeric type instead.

A type-mismatch error — correct the declaration to CHAR/VARCHAR, matching the specific character-requiring context that triggered it.