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fmCreate

fmCreate = 65535

Example​

procedure ReplaceFile(const FileName: String; Source: TStream);
var
  Dest: TFileStream;
begin
  Dest := TFileStream.Create(FileName, fmCreate);
  try
    Dest.CopyFrom(Source, 0, 65536);
  finally
    Dest.Free;
  end;
end;

Usage​

fmCreate creates or immediately truncates a file through TFileStream, using Velox's legacy all-bits-set value and forced exclusive sharing.

Effects and risk

  • This is not a probe for writability: an existing target can be destroyed merely by successful construction.
  • Later serialization, source reads, disk-full errors or write failures can leave an empty or partial file. The operation is not transactional or atomic publication.
  • Parent directories are not created. Invalid paths, permissions and incompatible existing handles raise from the constructor.
  • The returned stream owns the file handle and must be freed in finally; sharing restrictions last for that handle's lifetime.

Additional Technical Info​

fmCreate tells TFileStream.Create to create a missing file or truncate an existing file and return a read/write handle positioned at byte 0. Truncation happens inside the constructor, before any later script statement can succeed or fail.

Velox/Delphi compatibility quirk

Velox's Pascal Script import deliberately exposes the legacy value $FFFF (65535). Current Delphi declares fmCreate = $FF00. The compiled TFileStream recognises the all-bits-set legacy value, sees lower byte $FF, and remaps the share mode to fmShareExclusive before calling FileCreate.

Because every bit in $FFFF is already set, OR-ing fmCreate with an access or share constant cannot change the result. In Velox scripts, fmCreate or fmShareDenyNone is still $FFFF and still creates/truncates with exclusive sharing. Use fmCreate by itself so this is obvious.

Related entries

  • fmOpenWrite opens an existing file for in-place writing without constructor-time truncation.
  • fmOpenReadWrite opens an existing file for both reads and writes.

External references

Created 2026-07-15