Delphi in a Nutshell

Name

AssignFile Procedure

Syntax

procedure AssignFile(var F: File; const FileName: string);
procedure AssignFile(var F: TextFile; const FileName: string);

Description

Call AssignFile to assign a filename to a typed file, an untyped file, or a text file prior to opening the file. AssignFile is not a real procedure.

Tips and Tricks

• A subsequent call to Append, Reset, or Rewrite will open the file. If you do not call AssignFile first, a call to Append, Reset, or Rewrite causes Delphi to report I/O error 102.

• Delphi interprets an empty string as the console. In a console application, the Input and Output files are automatically assigned to the console. Trying to use a console file in a GUI application results in I/O error 105.

Example

var
  LogFile: string = 'c:\log.txt';

// Append a message to a log file. See the example with the Array
// Keyword for the other overloaded Log procedure.
procedure Log(const Msg: string); overload;
var
  F: TextFile;
begin
  AssignFile(F, LogFile);
  // Try to append to the file, which succeeds only if the file exists.
{$IoChecks Off}
  Append(F);
{$IoChecks On}
  if IOResult <> 0 then
    // The file does not exist, so create it.
    Rewrite(F);
  WriteLn(F, Msg);
  CloseFile(F);
end;

See Also

Append Procedure, CloseFile Procedure, Eof Function, File Type, IOResult Function, Reset Procedure, Rewrite Procedure, TextFile Type, $I Compiler Directive, $IOChecks Compiler Directive