String format procedure similar to writeln

Question

With writeln I can format numbers into a line of text.

var 
  file: text;
  mystring: string;

begin
  writeln(file,'Result is: ', var1:8:2,' | ', var2:8:2,' |');
end;

Is there a similar easy to use procedure in Delphi that would procedure similar result

  _format_string(mystring, 'Result is: ', var1:8:2,' | ', var2:8:2,' |');

Thank you.

Answer 1

You use the Format function:

mystring := Format('The image dimensions are %d × %d.', [640, 480]);

Answer 2

Technically the answer is "yes". But it's not recommended.

You can write your own text file device driver based on the System.TTextRec type.

I've done this in the past (especially in the Turbo Pascal era) for debugging purposes. It is a lot of work, and requires you to write a special MyAssign procedure, and be sure to close the Text file using the TTextRec in a try..finally block. Cumbersome, but doable.

A much easier alternative is using the Format function as described by Andreas Rejbrand.

The cool thing about using Format is that you use for Format Strings not only to parameterize things like width and precision inside that Format String, but also as paramaters like you normally would provide values.

You can get very close to using a width of 8 and a precision of 2, like the example in your question.

For instance, to quote the documentation:

Format ('%*.*f', [8, 2, 123.456]);

is equivalent to:

Format ('%8.2f', [123.456]);

That is a much overlooked feature of Format and Format Strings.