return statements with strings

WHSCT · December 27th, 2007, 09:22 PM

So here is the issue I have the book Professional C# 2005, (This is not a question on the book itself but rather I use an example to explain) and as I go through it I am keep on seeing some syntax that I don't full understand:

Code:

return string.Format("${0}.{1,-2:00}", Dollars,Cents)

now what I am confused about is how the ${0}.{1,-2:00} works and what it does?

weicco · December 28th, 2007, 03:58 AM

Well it is really simple, like printf in old C. Let's forget that ,-2:00 for a second...

{0} is replaced by the second parameter of String.Format (the first one is the format string)
{1} is replaced by the third parameter
... and so on

So let's say Dollars = 11 and Cents = 15, the return value would be "$11.15" String.Format has replaced those {n} placeholders (I'm not sure if placeholder is a correct term here) with actual values.

Now back to that ,-2:00 part in the second placeholder. It is formatting rule. How that second value should be formatted into the string. I just don't know what that -2:00 excatly does and I don't have time to check it out but you can check it from MSDN: http://msdn2.microsoft.com/en-us/library/fht0f5be.aspx

gunjan.sh · December 28th, 2007, 04:36 AM

In this statement
return string.Format("${0}.{1,-2:00}", Dollars,Cents)

{0} and {1} are placeholders which are replaced by the variables Dollars and Cents respectively.
And -2:00, formats the second placeholder to two decimal places .... ie, if u have a number say 5 and want to display it as 5.00,then u give the placeholder value say,{1:0.00}.
And -2 in -2:00 is indentation of the decimal points.
As far as i remember, -2 is indentation ... it means that 2 white spaces will be added to the right.If u give 20:00 it adds 20 white spaces to the left.Just check with it.
I hope u've atleast some idea. :)

Gunjan

WHSCT · December 28th, 2007, 08:49 PM

so why not just write soething like this... Preformance cant be the reason! so what do into all that?

return string.Format("$" + Dollars + "." + Cents);

planoie · December 29th, 2007, 01:21 AM

Using string.Format in this case doesn't add anything.

By doing only simple concatenation you don't get the output that you get with the use of string.Format().

Here are some examples of inputs and outputs using the two methods:

Code:

Inputs   Concat   Format()
--------------------------
5 24     $5.24    $5.24
0 2      $0.2     $0.02

String.Format() provides the formatting for each input value in the place holders in the string. In this case it is padding the cents value to 2 decimal places. In the case of simple concatenation, the above result could actually be interpreted wrong (20 cents instead of 02 cents).

There are measurable performance gains with the Format method over standard concatenation when you get into lots of string manipulation. But even for simple stuff it can be considerably easier to read and is a good habit to get into. When you build strings that contain quotes it becomes much easier to read. Consider the following examples:

   phrase = "I see";
   wife = "Gertrude";

   message = "\"" + phrase + "\", said the blind man to his deaf wife " + wife + ".";
      //vs.
   message = string.Format("\"{0}\", said the blind man to his deaf wife {1}.", phrase, wife);

The result is the same, and yes there is slightly more code using the Format() method. However, there is only 1 string literal instead of 3 (performance) and from my point of view it's easier to read the second to see the structure of the file string. As construction complexity grows, using the Format() method actually simplifies because you don't have to add more concatenation strings around variables. You just add a replacement token in the right place and another argument to the method call.

-Peter