Delphi Basics : Writeln command

DelphiBasics

Writeln
Procedure

Write a complete line of data to a text file

System unit

1	procedure Writeln(Expression1 {options} {, Expression2 {options} ...});
2	procedure Writeln (var FileHandle TextFile; Expression1 {options} {, Expression2 {options} ...};

Description

The WriteLn procedure writes a complete line of data to a text file or to the console.

Version 1

Is used to write a line of text to the console.

Version 2

Is used to write a line of text to a text file with the given FileHandle.

You must use AssignFile to assign a file to the FileHandle and open the file with Reset or ReWrite before using WriteLn.

The text written may be any valid Expression(s). Often these will be strings, but may also be expressions that result in strings or numbers.

After each expression, you can add formatting options:

:width	Field width for strings + numbers
:precision	Decimal digits for numbers

Notes

WriteLn does not buffer records, so performance is degraded. BlockWrite is more efficient, but is geared to writing to binary files.

Related commands

Append		Open a text file to allow appending of text to the end
AssignFile		Assigns a file handle to a binary or text file
BlockRead		Reads a block of data records from an untyped binary file
BlockWrite		Writes a block of data records to an untyped binary file
File		Defines a typed or untyped file
Read		Read data from a binary or text file
ReadLn		Read a complete line of data from a text file
Reset		Open a text file for reading, or binary file for read/write
ReWrite		Open a text or binary file for write access
TextFile		Declares a file type for storing lines of text
Write		Write data to a binary or text file

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Example code : Illustrating single, multiple and formatted text line writing

var
  myFile : TextFile;
  text   : string;

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

  // Write a couple of well known words to this file
  WriteLn(myFile, 'Hello World');

  // Write a blank line
  WriteLn(myFile);

  // Write a string and a number to the file
  WriteLn(myFile, '22/7 = ' , 22/7);

  // Repeat the above, but with number formatting
  WriteLn(myFile, '22/7 = ' , 22/7:12:6);

  // Close the file
  CloseFile(myFile);

  // Reopen the file for reading
  Reset(myFile);

  // Display the file contents
  while not Eof(myFile) do
  begin
    ReadLn(myFile, text);
    ShowMessage(text);
  end;

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

Show full unit code

  Hello World

  22/7 = 3.14285714285714E:0000
  22/7 = 3.142857