C#: String.Format("Format", Arguments) for .Net

This is my personal reference for String.Format().

Here are the quick reference tables.  Below are the explanations.

Format	Int 1234	Decimal 1234.567	Decimal 0.1234567	Decimal 1234.5
0:c	$1,234.00	$1,234.57	$0.12	$1,234.50
0:d	1234	-	-	-
0:e	1.234000e +003	1.234567e+003	1.234567e-001	1.234500e+003
0:f	1234.00	1234.57	0.12	1234.50
0:g	1234	1234.567	0.1234567	1234.5
0:n	1234.00	1,234.57	0.12	1,234.50
0:p	123,400.00 %	123,456.70 %	12.35 %	123,450.00 %
0:r	-	-	-	-
0:x	4d2	-	-	-
0:X	4D2	-	-	-
Padding/Precision:
0:d5	01234	-	-	-
0:e5	1.23400e+003	1.23457e+003	1.23457e-001	1.23450e+003
0:n5	1,234.00000	1,234.56700	0.12346	1,234.50000
0:c5	$1,234.00000	$1,234.56700	$0.12346	$1,234.50000
0:x5	004d2	-	-	-

Using: DateTime.Parse("December
13, 2008 5:01:30.7770 pm");

Format	DateTime (above date)	Jan 5 (rest same)	Description
0:D	Saturday, December 13, 2008	Wednesday, January 09, 2008	Long Date
0:F	Saturday, December 13, 2008 5:01:30 PM	Wednesday, January 09, 2008 5:01:30 PM	Full Date/Time (long time)
0:G	12/13/2008 5:01:30 PM	1/9/2008 5:01:30 PM	General Date/Time (long time)
0:M	December 13	January 09	Month Day
0:O	2008-12-13T17:01:30.7770000	2008-01-09T17:01:30.7770000	Round-Trip Date/Time
0:R	Sat, 13 Dec 2008 17:01:30 GMT	Wed, 09 Jan 2008 17:01:30 GMT	RFC1123
0:T	5:01:30 PM	5:01:30 PM	Long Time
0:U	Saturday, December 13, 2008 10:01:30 PM	Wednesday, January 09, 2008 10:01:30 PM	Universal Full Date/Time (long time)
0:Y	December, 2008	January, 2008	Year Month
0:d	12/13/2008	1/9/2008	Short Date
0:f	Saturday, December 13, 2008 5:01 PM	Wednesday, January 09, 2008 5:01 PM	Full Date/Time (short time)
0:g	12/13/2008 5:01 PM	1/9/2008 5:01 PM	General Date/Time (short time)
0:m	December 13	January 09	Month Day
0:o	2008-12-13T17:01:30.7770000	2008-01-09T17:01:30.7770000	Round-Trip Date/Time
0:r	Sat, 13 Dec 2008 17:01:30 GMT	Wed, 09 Jan 2008 17:01:30 GMT	RFC1123
0:s	2008-12-13T17:01:30	2008-01-09T17:01:30	Sortable Date/Time
0:t	5:01 PM	5:01 PM	Short Time
0:u	2008-12-13 17:01:30Z	2008-01-09 17:01:30Z	Universal Sortable Date/Time
0:y	December, 2008	January, 2008	Year Month

Useful Examples

Format	Use	Output
0:000-00-0000	SSN	012-34-5678
0:(###)###-####	US Phone Number	(555)555-5555
0:#-(###)###-####	US Phone Number	1-(555)555-5555
0:1-(###)###-####	US Phone Number	1-(555)555-5555

Formatting DateTime objects with DateTime.ToString("Format Here"):

Format	Description
d	Non-padded day
dd	Zero padded day
ddd	Short day name (Tue)
dddd	Full day name (Tuesday)
h	Non-padded hour 12 hour format
hh	Zero padded hour 12 hour format
H	Non-padded hour 24 hour format
HH	Zero padded hour 24 hour format
m	Non-padded minute
mm	Zero padded minute
M	Non-padded Month
MM	Zero padded Month
MMM	Short month name (Jun)
MMMM	Full month name (June)
s	Non-padded seconds
ss	Zero-padded seconds
tt	AM/PM
yy	2 digit year
yyyy	4 digit year
:	As is
/	As is
MM/DD/yyyy	Sample: 06/14/2008

You can customize the above with Number Customizations:

# is a digit place holder.

0 is a zero place holder.

. is a printed decimal point.

, is a printed comma.

% means use the number as a percentage where 1 is 100%.

If you want to have the actual number be the percentage, prefix the % with a '.
Example:

String.Format("{0:##.00'%",
12.34); // 12.34%

To do left and right padding:

String.Format("{0,-9}",
1234); // “1234 
“

String.Format("{0,9}", 1234); // “     1234“

The Basics

How to call String.Format(): String.Format("{ArgumentPosition,Padding}",
arguments[] or argument,argument…); 

String.Format("{0} {1}",
"Hello", "World");

Prints: Hello World

{0} and {1} are the positions of the arguments “Hello” and “World” specifying
where in the string they are top be used.

String.Format("First
Number: {0}, Third Number: {2}, Second Number: {1}.", 1,2,3);

Prints:
First Number: 1, Third Number: 3, Second Number: 2.

You do not have to call ToString() on your arguments, String.Format()
is smart enough to do that for us. Suppose you created your own Class called
Currency, which overrides ToString(). When your instance of Currency has a value of $19.95,
you can use:

String.Format("MyCurrency value:
{0}", myCurrency);

Prints: MyCurrency value: $19.95

Continue that thought just a little further... if you print DataRow information:

String.Format("Column
'ID': {0}", dr["ID"]);

C#: Performance: Boxing and Unboxing

You know to avoid boxing and unboxing wherever you can. Don't know what boxing is, read about it here[MSDN], but read on because you'll probably figure it out. Sometimes you can't avoid it, but other times, it can really be avoided so easily. Where?

ArrayList

Yep. ArrayList. If you are storing one type of object in ArrayList, why are you using it? You are wasting CPU cycles with boxing and unboxing. Include a reference to System.Collections and replace that snippet with a typed List.

ArrayList al = new ArrayList();

Becomes

List<DateTime> typedList = new List<DateTime>();

Now your gains won't be huge like replacing String with StringBuilder, but not only will you gain performance, but you now don't have to worry about type checking, either.

Why you should not throw Exceptions for normal Business Flow

You've heard it before and I'll tell you again, don't throw Exceptions for normal Business Logic because they are very expensive to process. It is so expensive that when you measure a return value of false verses a thrown exception, the return of false is nearly instantaneous verses a thrown exception is about 4 orders of magnitude slower.

Use booleans or other return value types to determine failure in business logic processing and only throw Exceptions when you are truly in an Exception condition.

What is an Exception condition? It's a condition where continuing to process is impossible and notification must be immediate. When you use SqlTransaction or TransactionScope, it's a quick and easy way to rollback the transaction and handle the exception in one easy step.

A great example of an Exception condition is where you retrieve data from a database and you really expected data to be there. You cannot continue processing because that data is necessary to continue.

Code:

DateTime startTime = DateTime.Now;
for (int i = 0; i < 1000; i++)
{

    try
    {
        throwException();
    }
    catch (Exception)
    {
    }

}
DateTime endTime = DateTime.Now;

Console.WriteLine("avg milliseconds for throwing: " + endTime.Subtract(startTime).TotalMilliseconds / 1000);

startTime = DateTime.Now;
for (int i = 0; i < 1000; i++)
{
    returnFalse();

}
endTime = DateTime.Now;

Console.WriteLine("avg milliseconds for returning: " + endTime.Subtract(startTime).TotalMilliseconds / 1000);