IsInteger

Function IsInteger( const S : string) : Boolean

Example

procedure ScriptEvent(var Value: variant);
begin
  Value := IsInteger('0042');
end;

Usage

IsInteger checks that non-empty text consists only of ASCII decimal digits.

Parameters

Name	Type	Description
S	string, const	Text to inspect exactly as supplied.

Returns

True when the nonempty inspected prefix contains only ASCII digits; otherwise False.

Behaviour

Leading zeroes are accepted. A plus or minus sign is not accepted, and neither are spaces, decimal points, group separators or exponent notation.

Errors

The lexical scan has no normal exception path. A subsequent numeric conversion can still raise an invalid-value or overflow exception.

Usage notes

After this check, use the integer conversion and range required by the destination and handle conversion failure. If signed integers are permitted, validate the optional leading sign explicitly or use a parser with documented format rules.

Additional Technical Info

IsInteger checks whether a nonempty string consists only of the ASCII characters 0 through 9. It validates a lexical shape; it does not convert the text or prove that it fits a Velox/Delphi integer type.

The example returns True. It is source-reviewed and is not executed by the documentation workflow.

Implementation

The Velox implementation returns False for S = '', then scans a PChar until a null character. Each character must belong to the Delphi set ['0'..'9'].

Edge cases and quirks

• -1, +1, 1, 1 , 1.0 and 1,000 all return False.
• Unicode digits outside ASCII 0 through 9 return False.
• There is no length or range check. A string containing thousands of digits can return True and still overflow every available integer conversion.
• An embedded #0 ends the pointer scan. Characters after it are ignored; a nonempty string whose first character is #0 can return True.
• The result does not distinguish identifiers with leading zeroes from canonical decimal representations.

Side effects

None.

Performance and concurrency

Time is linear in the inspected prefix. No transformed string is allocated and no shared mutable state is used.

Related entries

• IsNumber permits an optional leading sign and one period.
• IsCurrencyNumber is a broader punctuation whitelist.
• Comparison explains why these lexical helpers are not numeric parsers.

Created 2026-07-15