Simple C# stringformatting question

Question

I have a case where I need to be able to convert a float to a string using a formatter that will not be known until runtime. I thought that this would be simple. However, I am having problems coming up with the correct format string for fixed width, right justified padded on left with spaces. Here is a stripped down simplified demonstration of my problem:

namespace ConsoleApp
{

  class Program
  {
    public static void FormatHandler( string Formatter, float Value)
    {
      // Simple stripped down functionality for now; format the value
      // accoring to Formatter and print.
      string OutputStr = Value.ToString( Formatter ) ;
      Console.WriteLine(OutputStr);
    }


    static void Main(string[] args)
    {
      // Test the format handler method (in real life the formatter could be
      // runtime dependent, e.g. it could come from a database or configuration
      // file or other).
      float Val = 23.592f ;

      FormatHandler( "F", Val ) ;   // Simple case, default float conversion.
      FormatHandler( "F1", Val ) ;  // Only one decimal place please.


      // How do I do fixed width, padding with space if necessary on the left?
      // For example, I want the resultant string to be five characters wide and
      // one D.P. " 23.5". Here are my attempts...


      // Nope print "5:F1" not " 23.5".
      FormatHandler( "5:F1", Val ) ;

      // Nope. Better, but padded with leading zeros not spaces.
      FormatHandler ( "000.0", Val ) ;

      // Nope. You would have thought, but looks the same as "F1"
      FormatHandler ( "###.#", Val ) ;

      // There must be a way?
    }

  }
}

Answer 1

Hello @Viorel ,

Thank you so much for spending the time to help me. The solution you offer can be made to work, but then does require an extra parameter. I have been trying to work out ways that do not need an extra width parameter, and just use the Formatter parameter. I have been battling with the C# formatters, and unless I have misunderstood things, it seems that they behave differently in different situations. (Nothing beats the good old C language "printf" formatters; consistent and you could always get exactly what you wanted :-) ).

So here is the solution I am going with. It has the disadvantage of being clunky, I have to change the simple formatters (from "F" to "0:F" etc), and it does not work with all formats. Rather unsatisfactory, but for what I am doing sufficient:

namespace ConsoleApp  
{  
  
  class Program  
  {  
    public static void FormatHandler( string Formatter, float Value)  
    {  
      string TmpStr = "{0," + Formatter + "}" ;  
      string OutputStr = string.Format( TmpStr, Value ) ;  
      Console.WriteLine(OutputStr);  
    }  
  
  
  
    static void Main(string[] args)  
    {  
      // Test the format handler method (in real life the formatter could be  
      // runtime dependent, e.g. it could come from a database or configuration  
      // file).  
      float Val = 23.592f ;  
  
      FormatHandler( "0:F", Val ) ;   // Simple case, default float conversion.  
      FormatHandler( "0:F1", Val ) ;  // Only one decimal place please.  
  
  
      // How do I do fixed width, padding with space if necessary on the left?  
      // For example, I want the resultant string to be five characters wide and  
      // one D.P. " 23.5". Here are my attempts...  
      FormatHandler( "5:F1", Val ) ;  
  
    }  
  
  }  
}  

Once again, thank you for your time.

Answer 2

Check an example:

string s = string.Format( "{0,5:F1}", Val );

You can write a FormatHandler that accepts “5:F1” as parameter and uses string.Format.

Or you can do this:

public static void FormatHandler( string Formatter, float Value, int width = 0 )
{
   string OutputStr = Value.ToString( Formatter );
   if( width > 0 ) OutputStr = OutputStr.PadLeft( width );
   Console.WriteLine( OutputStr );
}
. . .
FormatHandler( "F1", Val, 5 );