对于int，double等的tostring：

C	货币	2.5.ToString("C")	￥2.50
D	十进制数	25.ToString("D5")	00025
E	科学型	25000.ToString("E")	2.500000E+005
F	固定点	25.ToString("F2")	25.00
G	常规	2.5.ToString("G")	2.5
N	数字	2500000.ToString("N")	2,500,000.00
X	十六进制	255.ToString("X")	FF

格式符	应 用	含 义	示 例
C	数字类型	专用场合的货币值	$4834.50 (USA) £4834.50 (UK)
D	只用于整数类型	一般的整数	4834
E	数字类型	科学计数法	4.834E+003
F	数字类型	小数点后的位数固定	4384.50
G	数字类型	一般的数字	4384.5
N	数字类型	通常是专用场合的数字 格式	4,384.50 (UK/USA) 4 384,50 (欧洲大陆)
P	数字类型	百分比计数法	432,000.00%
X	只用于整数类型	16进制格式	1120 (如果要显示0x1120，需要写上0x)

Custom number formatting:

 

 

Specifier	Type	Example	Output (Passed Double 1500.42)	Note
0	Zero placeholder	{0:00.0000}	1500.4200	Pads with zeroes.
#	Digit placeholder	{0:(#).##}	(1500).42
.	Decimal point	{0:0.0}	1500.4
,	Thousand separator	{0:0,0}	1,500	Must be between two zeroes.
,.	Number scaling	{0:0,.}	2	Comma adjacent to Period scales by 1000.
%	Percent	{0:0%}	150042%	Multiplies by 100, adds % sign.
e	Exponent placeholder	{0:00e+0}	15e+2	Many exponent formats available.
;	Group separator	see below

 

The group separator is especially useful for formatting currency values which require that negative values be enclosed in parentheses. This currency formatting example at the bottom of this document makes it obvious:

Dates

Note that date formatting is especially dependant on the system's regional settings; the example strings here are from my local locale.

 

 

Specifier	Type	Example (Passed System.DateTime.Now)
d	Short date	10/12/2002
D	Long date	December 10, 2002
t	Short time	10:11 PM
T	Long time	10:11:29 PM
f	Full date & time	December 10, 2002 10:11 PM
F	Full date & time (long)	December 10, 2002 10:11:29 PM
g	Default date & time	10/12/2002 10:11 PM
G	Default date & time (long)	10/12/2002 10:11:29 PM
M	Month day pattern	December 10
r	RFC1123 date string	Tue, 10 Dec 2002 22:11:29 GMT
s	Sortable date string	2002-12-10T22:11:29
u	Universal sortable, local time	2002-12-10 22:13:50Z
U	Universal sortable, GMT	December 11, 2002 3:13:50 AM
Y	Year month pattern	December, 2002

 

The 'U' specifier seems broken; that string certainly isn't sortable.

Custom date formatting:

 

 

Specifier	Type	Example	Example Output
dd	Day	{0:dd}	10
ddd	Day name	{0:ddd}	Tue
dddd	Full day name	{0:dddd}	Tuesday
f, ff, ...	Second fractions	{0:fff}	932
gg, ...	Era	{0:gg}	A.D.
hh	2 digit hour	{0:hh}	10
HH	2 digit hour, 24hr format	{0:HH}	22
mm	Minute 00-59	{0:mm}	38
MM	Month 01-12	{0:MM}	12
MMM	Month abbreviation	{0:MMM}	Dec
MMMM	Full month name	{0:MMMM}	December
ss	Seconds 00-59	{0:ss}	46
tt	AM or PM	{0:tt}	PM
yy	Year, 2 digits	{0:yy}	02
yyyy	Year	{0:yyyy}	2002
zz	Timezone offset, 2 digits	{0:zz}	-05
zzz	Full timezone offset	{0:zzz}	-05:00
:	Separator	{0:hh:mm:ss}	10:43:20
/	Separator	{0:dd/MM/yyyy}	10/12/2002

 

Enumerations

 

 

Specifier	Type
g	Default (Flag names if available, otherwise decimal)
f	Flags always
d	Integer always
x	Eight digit hex.

 

Some Useful Examples

String.Format("{0:$#,##0.00;($#,##0.00);Zero}", value);

This will output "$1,240.00" if passed 1243.50. It will output the same format but in parentheses if the number is negative, and will output the string "Zero" if the number is zero.
String.Format("{0:(###) ###-####}", 18005551212);

This will output "(800) 555-1212".

变量.ToString()

字符型转换 转为字符串
12345.ToString("n"); //生成 12,345.00
12345.ToString("C"); //生成 ￥12,345.00
12345.ToString("e"); //生成 1.234500e+004
12345.ToString("f4"); //生成 12345.0000
12345.ToString("x"); //生成 3039 (16进制)
12345.ToString("p"); //生成 1,234,500.00%