Delphi Basics : Seek command

DelphiBasics

Seek
Procedure

Move the pointer in a binary file to a new record position

System unit

procedure Seek(var FileHandle File; RecordNumber LongInt);

Description

The Seek procedure moves the current record position in an open binary file given by FileHandle to a new position RecordNumber.

The file must have been assigned with AssignFile and opened with Reset or ReWrite.

For untyped files, the record size is set with the Reset or ReWrite routine used.

For typed files, the record size is SizeOf the file type.

The first record in a file is record 0.

Notes

Use SeekEoln or SeekEof to move the file pointer on a text file.

Related commands

Eof		Returns true if a file opened with Reset is at the end
Eoln		Returns true if the current text file is pointing at a line end
File		Defines a typed or untyped file
FilePos		Gives the file position in a binary or text file
SeekEoln		Skip to the end of the current line or file

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Example code : Repositioning in a Word type file

var
  myWord, myWord1, myWord2, myWord3, myWord4 : 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 := 12;
  myWord2 := 34;
  myWord3 := 56;
  myWord4 := 78;
  Write(myFile, myWord1, myWord2, myWord3, myWord4);

  // Close the file
  CloseFile(myFile);

  // Reopen the file for read only purposes
  FileMode := fmOpenRead;
  Reset(myFile);

  // Seek (move) to the start of the 3rd record
  Seek(myFile, 2);    // Records start from 0

  // Show this record
  Read(myFile, myWord);
  ShowMessage('Record 3 = '+IntToStr(myWord));

  // Close the file
  CloseFile(myFile);
end;

Show full unit code

Record 3 = 56