在写程序的过程中我们常常会遇到格式化字符串呀啥的，如:DataTime.ToString("yyyy-MM-dd")等，当然最常用的应该是String.Format了，非常方便好用！
但有时有些格式记不住，只要认真分析这个规律，其实它很好记，很快就掌握了，我特意收集起来，希望对大家有所帮助！
C#格式化数值结果表
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字符 -------- 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
真的没有任何格式在一个强大的、超越它的位置。如有任何争议对齐的作品被印刷在一个字符串：
String.Format("->{1,10}<-", "Hello"); -> Hello<-
String.Format("->{1,-10}<-", "Hello"); ->Hello <-
Numbers
基本的数字格式：
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
x Hexadecimal {0:x4} System.
FormatException cf90
特殊类型的例子输出：
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:
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
g Default (Flag names if available, otherwise decimal)
f Flags always
d Integer always
x Eight digit hex.
几个有用的例子：
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%
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