DELPHI - How change file extension

var
  sFileName : string;
begin
  ...
  sFileName := 'c:\temp\file.txt';
  ShowMessage( sFileName + #13 + changeFileExt( sFileName, '.exe' ) );

Output:

DELPHI - How check if file exists

var
  sPath : string;
begin
  ...
  if not FileExists( sPath ) then
    begin
      MessageDlg( Format( 'File "%s" not found.', [sPath] ), mtError, [mbOk], 0 );
      exit;
    end;
  ...
end;

DELPHI - How copy file

First parameter is source file, second parameter is target location.

_sFileName : string
..
copyfile( PChar( _sFileName ), PChar( IncludeTrailingPathDelimiter( EPath.Text ) + 
          ExtractFileName( _sFileName ) ), false );

DELPHI - How to generate file with record based type

When you need save some complex record type to file you can use this code:

{ header of admin file }
TRecFileAdmin = record
  sIdent              : string[15] ;
  dDateTo             : TDateTime;
end;
...
{ ---------------------------------------------------------------------------
  Function generate admin file into _FileName file.
  -------------------------------------------------------------------------- }
function GenerateAdminFile( _sFileName : string ) : boolean;
var
  f : TFile;
  recFileAdmin : TRecFileAdmin;
begin
  result := false;

  try
    try
      { every time establish new }
      f := TFile.Create( _sFileName, true );

      { three day validity }
      FillChar( recFileAdmin, sizeof( recFileAdmin ), 0 );
      recFileAdmin.sIdent  := gcsIdent;
      recFileAdmin.dDateTo := Now + 3;  
      f.FileWrite( recFileAdmin, sizeof( recFileAdmin ) );
    except
      on E : exception do
        begin
          doError( ERROR_SAVE, [ 'A9Admin.GenerateAdmin()', E.Message ] );
          exit;
        end;
    end;
  finally
    f.free;
  end;

  result := true;
end;