Informix Error -4156: Warning: The loop counter may overflow.

Cause and resolution

Warning: The loop counter may overflow.

This warning can occur for a FOR statement when the upper limit of the FOR loop is within the STEP value of the maximum value of that type. As an example, suppose the FOR statement tried to run IX from 1 to 32760 with a step of 20, and IX was declared as SMALLINT; the compiler would issue the warning because IX would overflow without satisfying the loop termination condition.

Oninit® Troubleshooting Guidance

Reasons / Common Causes

-4156 is a compiler warning: per the official guidance, this can occur for a FOR statement when the loop's upper limit is within the STEP value of that type's maximum. For example, a SMALLINT loop counter running from 1 to 32760 with a step of 20 would overflow before satisfying the loop's termination condition.

A FOR loop counter whose upper limit is close enough to its type's maximum that the STEP could overshoot it, per the official guidance — the direct cause.

Solutions / Resolution

Use a wider integer type for the loop counter, or adjust the loop's bounds/step so it can't overflow.

Examples

A loop counter close to overflow

DEFINE ix SMALLINT
FOR ix = 1 TO 32760 STEP 20
  ...
END FOR
-- -4156: ix may overflow SMALLINT's maximum before the loop terminates

Corrected

DEFINE ix INTEGER
FOR ix = 1 TO 32760 STEP 20
  ...
END FOR

Diagnostic Checks

Check every FOR loop's counter type, upper limit, and step for the possibility of overflow, and widen the type or adjust the bounds if needed.

Related Errors / Related Topics

No closely related error codes are cross-referenced for -4156 in this set yet.

A FOR loop's counter may overflow its declared type before the loop terminates — widen the type or adjust the bounds/step.