Displaying the Percentage Character in Delphi's Format function

Fixing Delphi's: "Format '% ' invalid or incompatible with argument"

Delphi's Format (declared in the SysUtils unit) function can be used to construct a formatted string assembled from a format string and an array of arguments (open array).

Declared in two overloads as

function Format(const Format: string; const Args: array of const): string; overload;

function Format(const Format: string; const Args: array of const; const FormatSettings: TFormatSettings): string; overload;

The second version uses the TFormatSettings type variable which refers to localization information contained in the FormatSettings parameter.

To display a number, you can use the next code:

var
  s : string;
begin
  s := Format('3 divided with 7 (using 2 decimal places) is %.2f',[3/7]) ;

  ShowMessage(s) ;

Note the usage of the percentage character. The "%.2f" is the format string to be used when formatting the value "3/7" and converting to a string.

Displaying the Percentage Sign (%)

A beginner Delphi developer might have problems with a line like:

Format('In percentage the value is %.2f %',[3/7]) ;

The last percentage sign will NOT be a part of the resulting string.

To fix this "problem" you simply need to use two % characters, as in

Format('In percentage the value is %.2f %%',[3/7]) ;

What's more, if you forget about the need to use the two % characters to make the Format function display the percentage sign, aline like this one will result in the "Format '% ' invalid or incompatible with argument".

Format('3 % of 7 is %.2f',[3/7]) ;

To fix this, simply use two % characters, as in:

Format('3 %% of 7 is %.2f',[3/7]) ;

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