How to use String.format in .NET?

example	output
String.Format(“–{0,10}–”, “test”);	–      test–
String.Format(“–{0,-10}–”, “test”);	–test      –

Number formatting is culture dependant. For example, formatting a currency string on a system with regional settings to UK will return a result like £9.99, formatting a currency on a machine set for the US region would return $9.99.

specifier	type	format	output(double 1.2345)	output(int -12345)
c	currency	{0:c}	£1.23	-£12,345.00
d	decimal(whole number)	{0:d}	System.FormatException	-12345
e	exponent / scientific	{0:e}	1.234500e+000	-1.234500e+004
f	fixed point	{0:f}	1.23	-12345.00
g	general	{0:g}	1.2345	-12345
n	number	{0:n}	1.23	-12,345.00
r	round trippable	{0:r}	1.23	System.FormatException
x	hexadecimal	{0:x4}	System.FormatException	ffffcfc7

custom number formatting

specifier	type	format	output(double 1234.56)
0	zero placeholder	{0:00.000}	1234.560
#	digit placeholder	{0:#.##}	1234.56
.	decimal point placeholder	{0:0.0}	1234.6
,	thousand separator	{0:0,0}	1,235
%	percentage	{0:0%}	123456%

In addition there is the group separator; this is useful for varying the format, depending on the value of the parameter passed. For example

String.Format("{0:£#,##0.00;(£#,##0.00);Nothing}", value);

This will output “£1,240.00″ if passed 1243.56.  It will output the same format bracketed if the value is negative “(£1,240.00)”, and will output the string “Nothing” if the number is zero.

date formatting

Date formats are very dependant on the culture information passed. The examples below are shown using the UK culture.

specifier	type	output(June 8, 1970 12:30:59)
d	Short Date	08/06/1970
D	Long Date	08 June 1970
t	Short Time	12:30
T	Long Time	12:30:59
f	Full date and time	08 June 1970 12:30
F	Full date and time (long)	08 June 1970 12:30:59
g	Default date and time	08/06/1970 12:30
G	Default date and time (long)	08/06/1970 12:30:59
M	Day / Month	8 June
r	RFC1123 date string	Mon, 08 Jun 1970 12:30:59 GMT
s	Sortable date/time	1970-06-08T12:30:59
u	Universal time, local timezone	1970-06-08 12:30:59Z
Y	Month / Year	June 1970

custom date formatting

specifier	type	output(June 8, 1970 12:30:59)
dd	Day	08
ddd	Short Day Name	Mon
dddd	Full Day Name	Monday
hh	2 digit hour	12
HH	2 digit hour (24 hour)	12
mm	2 digit minute	30
MM	Month	06
MMM	Short Month name	Jun
MMMM	Month name	June
ss	seconds	59
tt	AM/PM	PM
yy	2 digit year	70
yyyy	4 digit year	1970
:	seperator, e.g. {0:hh:mm:ss}	12:30:59
/	seperator, e.g. {0:dd/MM/yyyy}	08/06/1970

There are others, including time zone formatting and so on, but the ones above are the most commonly used.