StrToUInt64Def

function StrToUInt64Def(S: string; def: UInt64): UInt64;

Example

procedure ScriptEvent(var Value: variant);
begin
  Value := StrToUInt64Def('-1', 0);  // 0
end;

Usage

StrToUInt64Def parses text as an unsigned 64-bit integer, returning a supplied value on failure.

Parameters

Name	Type	Description
S	string	Unsigned decimal or $/0x hexadecimal text for a UInt64 destination.
def	UInt64	Value returned for malformed, negative, partial or out-of-range input.

Returns

The parsed value in 0..18446744073709551615, or def when conversion fails.

Errors

Ordinary conversion failures return def. Allocation or unexpected runtime failures can still propagate.

Usage notes

Use a fallback outside the valid business domain where possible. The type itself has no spare sentinel, so retain a separate validity flag when every UInt64 value is meaningful.

Additional Technical Info

StrToUInt64Def parses decimal or Delphi-style hexadecimal text into UInt64 and returns def when conversion fails. It accepts the complete unsigned 64-bit range and suppresses the ordinary conversion exception raised by StrToUInt64.

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

Implementation

With PascalScript 64-bit integer support enabled, runtime dispatch case 47 reads both stack arguments and calls Delphi System.SysUtils.StrToUInt64Def. That routine calls intrinsic Val with a UInt64 destination and substitutes def whenever Val returns a non-zero error position.

Edge cases and quirks

• Negative decimal input is outside the destination range and returns def; it is not wrapped modulo 2^64.
• The maximum UInt64 value is a valid result. A decimal value one greater than the maximum returns def.
• Hexadecimal input can use all 64 bits without becoming negative because the destination is unsigned.
• Syntax failure and numeric overflow share the same fallback path, and the original Val error position is not exposed.
• A valid value equal to def is indistinguishable from failure.
• Free Pascal's direct routine has the same broad fallback purpose but documents dialect-specific prefix rules. The installed Delphi terminal remains authoritative.
• The function is present because the current PascalScript build enables Int64/UInt64 support.

Side effects

None.

Performance and concurrency

Linear in input length and independent of locale, I/O and shared mutable state.

Related entries

• StrToUInt64 raises on the same conversion failures.
• StrToInt64Def parses the signed 64-bit range.
• UIntToStr formats the current script UInt64 as decimal text.

External references

• Free Pascal StrToUInt64Def - compatible unsigned fallback reference with dialect-specific parser details.
• Embarcadero System.SysUtils.StrToUInt64Def - the exact Delphi terminal called by PascalScript.

Created 2026-07-15