Delphi Basics : Truncate command

DelphiBasics

Truncate
Procedure

Truncates a file size - removes all data after the current position

System unit

procedure Truncate(var FileHandle File);

Description

The Truncate procedure truncates a file at the current file position. All data after the current file position is erased.

The file must have been assigned using Assign and opened using RewRite or Reset.

Text files are not supported.

Related commands

Append		Open a text file to allow appending of text to the end
Erase		Erase a file
FilePos		Gives the file position in a binary or text file

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Example code : Write to a file, then truncate it

var
  myWord, myWord1, myWord2 : Word;
  myFile : File of Word;

begin
  // Try to open the Test.bin binary file for writing to
  AssignFile(myFile, 'Test.cus');
  ReWrite(myFile);

  // Write a couple of Words to the file
  myWord1 := 234;
  myWord2 := 567;
  Write(myFile, myWord1, myWord2);

  // Close the file
  CloseFile(myFile);

  // Display the file contents
  Reset(myFile);
  ShowMessage('Before truncate :');
  while not Eof(myFile) do
  begin
    Read(myFile, myWord);
    ShowMessage(IntToStr(myWord));
  end;

  // Close, reopen, and truncate after the first word
  CloseFile(myFile);
  FileMode := 2;
  Reset(myFile);
  Read(myFile, myWord);
  Truncate(myFile);
  CloseFile(myFile);

  // Display the file contents again
  Reset(myFile);
  ShowMessage('After truncate :');
  while not Eof(myFile) do
  begin
    Read(myFile, myWord);
    ShowMessage(IntToStr(myWord));
  end;

  // Close the file for the last time
  CloseFile(myFile);
end;

Show full unit code

  Before truncate :
  234
  567
  After truncate :
  234