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StrToFloatDef

function StrToFloatDef(const S: string; const Default: Extended): Extended;

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := StrToFloatDef('not-a-number-value', -1.0);  // -1.0
end;

Usage​

StrToFloatDef uses the public Velox-compatible alias to parse system-locale text as Extended, returning the supplied fallback on ordinary failure.

Parameters

NameTypeDescription
SstringFloating text interpreted with the Windows system locale's decimal separator.
DefaultExtendedValue returned when the complete input cannot be converted. It is returned unchanged and can itself be zero, infinity or NaN.

Returns

The parsed Extended value on success; otherwise Default. The return alone cannot distinguish a successful conversion from failure when the parsed value equals the fallback.

Errors

Ordinary syntax, separator and range failures return Default. Allocation failures or other unexpected runtime exceptions are not promised to be swallowed.

Usage notes

Use this function when the fallback is part of the data contract. If malformed text must be logged, rejected or distinguished from a legitimate fallback value, use a try-style conversion and handle its Boolean result.

Additional Technical Info​

StrToFloatDef parses an Extended value with Velox's Windows system-locale policy and returns Default if parsing fails. It is the non-raising companion to StrToFloat, with the same accepted grammar and precision constraints.

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

Implementation

The scripting registration maps the public name to Velox vxStrToFloatDef. Each call creates TFormatSettings with LOCALE_SYSTEM_DEFAULT and invokes Delphi System.SysUtils.StrToFloatDef(S, Default, AFormatSettings). The Delphi overload attempts the same text-to-floating conversion as StrToFloat and assigns Default when that attempt returns false.

Edge cases and quirks

  • Decimal punctuation depends on the Windows system locale. Thousands separators and currency symbols remain invalid even when they are defined by that locale.
  • Leading and trailing ASCII spaces are accepted for ordinary numeric forms; partial values or trailing non-space characters fail as a whole.
  • The installed Delphi terminal accepts NAN, INF, +INF and -INF as successful special values, so Default is not used for those tokens.
  • Precision and finite range depend on the compiled Delphi target's Extended representation.
  • A fallback such as 0 or -1 can also be a legitimate parsed value. The API exposes no success flag; use vxTryStrToFloat when the distinction is essential.
  • Free Pascal's similarly named routine has a compatible high-level fallback contract, but Velox's system-locale wrapper and Delphi special-value behaviour remain authoritative.

Side effects

None outside local format-settings construction and temporary parsing state.

Performance and concurrency

Time is linear in input length plus the cost of obtaining system-locale settings for each call. The explicit local settings record avoids Delphi global-format races; subsequent calls can reflect an operating-system locale change.

Related entries

  • StrToFloat raises rather than returning a fallback.
  • FloatToStr converts in the other direction with Velox's system-locale settings.
  • vxTryStrToFloat reports success separately and is documented in its own later Conversion entry.

External references

Created 2026-07-15