说明
示例
输出

C 货币 string.Format("{0:C3}", 2) ＄2.000
D 十进制 string.Format("{0:D3}", 2) 002
E 科学计数法 1.20E+001 1.20E+001
G 常规 string.Format("{0:G}", 2) 2
N 用分号隔开的数字 string.Format("{0:N}", 250000) 250,000.00
X 十六进制 string.Format("{0:X000}", 12) C

string.Format("{0:000.000}", 12.2) 012.200
Strings
There really isn't any formatting within a strong, beyond it's alignment. Alignment works for any argument being printed in a String.Format call.
Sample Generates
String.Format("->{1,10}<-", "Hello"); -> Hello<-
String.Format("->{1,-10}<-", "Hello"); ->Hello <-

Numbers
Basic number formatting specifiers:
Specifier Type Format  Output
(Passed
Double 1.42)
Output
(Passed
Int -12400)

c Currency {0:c} ＄1.42 -＄12,400
d Decimal (Whole number) {0:d} System.
FormatException -12400
e Scientific {0:e} 1.420000e+000 -1.240000e+004
f Fixed point {0:f} 1.42 -12400.00
g General {0:g} 1.42 -12400
n Number with commas for thousands {0:n} 1.42 -12,400
r Round trippable {0:r} 1.42 System.
FormatException
FormatException cf90

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".

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%
Dim MyDateTime As Date = #1/27/2001 5:04:23 PM#
Dim MyStr As String
' Returns current system time in the system-defined long time format.
MyStr = Format(Now(), "Long Time")
' Returns current system date in the system-defined long date format.
MyStr = Format(Now(), "Long Date")
' Also returns current system date in the system-defined long date
' format, using the single letter code for the format.
MyStr = Format(Now(), "D")
' Returns the value of MyDateTime in user-defined date/time formats.
MyStr = Format(MyDateTime, "h:m:s")   ' Returns "5:4:23".
MyStr = Format(MyDateTime, "hh:mm:ss tt")   ' Returns "05:04:23 PM".
MyStr = Format(MyDateTime, "dddd, MMM d yyyy")   ' Returns "Saturday,
' Jan 27 2001".
MyStr = Format(MyDateTime, "HH:mm:ss")   ' Returns "17:04:23"
MyStr = Format(23)   ' Returns "23".
' User-defined numeric formats.
MyStr = Format(5459.4, "##,##0.00")   ' Returns "5,459.40".
MyStr = Format(334.9, "###0.00")   ' Returns "334.90".
MyStr = Format(5, "0.00%")   ' Returns "500.00%".

(0)

(#)

(.)

(%)

(,)

(:)

(/)

(E- E+ e- e+)

- + \$ ( )

(\)

("ABC")