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ExtractFileDir

Function ExtractFileDir( const FileName : string) : string

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := ExtractFileDir('C:\Fictional\Inbound\order.csv');
  // C:\Fictional\Inbound
end;

Usage​

ExtractFileDir returns the drive and directory portion of a file-name string without its trailing separator in ordinary cases.

Parameters

NameTypeDescription
FileNamestring, constFile-name or path text to parse. It may be absolute, drive-relative or relative.

Returns

The parsed drive/directory text, or an empty string when no recognised path or drive delimiter occurs.

Behaviour

  • 'C:\Folder\file.txt' returns 'C:\Folder'.
  • 'C:\file.txt' returns 'C:\', preserving the drive root.
  • 'C:file.txt' returns 'C:'; that remains a drive-relative prefix, not a drive-root path.
  • 'file.txt' returns ''.
  • The result is computed from text even when no such directory exists.

Errors

There is no normal path-content exception. String conversion or allocation failures can propagate.

Usage notes

Use this result when an API expects a directory name without an ordinary trailing separator. Use ExtractFilePath when the result will be concatenated directly with another relative name.

Additional Technical Info​

ExtractFileDir returns the drive and directory portion parsed from FileName. Unlike ExtractFilePath, it normally omits the trailing path delimiter so the result can be used as a directory name.

The example is source-reviewed and was not executed by the documentation workflow. No path existence check occurs.

Implementation

The Velox wrapper calls installed System.SysUtils.ExtractFileDir. On Windows the RTL locates the final backslash or drive colon. When the final delimiter is a backslash whose preceding character is neither a backslash nor a colon, it steps back one character before copying the prefix. That rule removes an ordinary trailing separator while retaining drive-root and paired-separator forms.

Edge cases and quirks

  • This is not the same operation as removing the final delimiter from ExtractFilePath for every root/UNC case; the installed implementation has explicit preceding-character rules.
  • A path ending in an ordinary directory separator is treated as directory text and normally returned without that final separator.
  • On Windows, forward slashes are not part of the terminal delimiter set. URL-style or mixed-separator input can parse unexpectedly.
  • . and .. segments, duplicate separators, environment variables and relative prefixes are not resolved.
  • UNC, extended-length and device prefixes are preserved lexically; the routine does not verify that the share or device exists.

Side effects

None.

Performance and concurrency

The routine scans backward and copies a prefix, making work linear in the path length. It has no mutable shared state.

Related entries

External references

Created 2026-07-15