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
 
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