Delphi Basics : FilePos command

DelphiBasics

FilePos
Function

Gives the file position in a binary or text file

System unit

1	function FilePos(var FileHandle File;):LongInt;
2	function FilePos (var FileHandle TextFile;;

Description

The FilePos function returns the current position in an open file. The returned value is the Record position, starting at 0 for the file beginning.

The file may be an Untyped, Typed or Text file.

The record length is as follows:

Untyped files	: As set in Reset or ReWrite
Typed files	: SizeOf the file type
Text files	: Variable - defined by line ends

Notes

Seek to the given record position only works for binary files.

Related commands

Eoln		Returns true if the current text file is pointing at a line end
File		Defines a typed or untyped file
Seek		Move the pointer in a binary file to a new record position
SeekEoln		Skip to the end of the current line or file
TextFile		Declares a file type for storing lines of text

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Example code : Show the file position in a binary file

var
  myWord, myWord1, myWord2, myWord3 : Word;
  myFile : File of Word;

begin
  // Try to open the Test.cus binary file in write only mode
  AssignFile(myFile, 'Test.cus');
  ReWrite(myFile);

  // Write a few lines of Word data to the file
  myWord1 := 123;
  myWord2 := 456;
  myWord3 := 789;
  Write(myFile, myWord1, myWord2, myWord3);

  // Close the file
  CloseFile(myFile);

  // Reopen the file in read only mode
  FileMode := fmOpenRead;
  Reset(myFile);

  // Display the file contents
  while not Eof(myFile) do
  begin
    Read(myFile, myWord);
    // Note - FilePos shows the after read position
    ShowMessage('Record '+
                IntToStr(FilePos(myFile))+' = '+
                IntToStr(myWord));
  end;

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

Show full unit code

  Record 1 = 123
  Record 2 = 456
  Record 3 = 789