一、定义
String.Format是将指定的 String类型的数据中的每个格式项替换为相应对象的值的文本等效项。
如:
（1）这二者的效果是一样的。都是将最后面的两项的值分别替换第一项的{0}和{1}。
string p1 = "Jackie";
string p2 = "Aillo";
Response.Write(String.Format("Hello {0}, I'm {1}", p1, p2));
（2）
Response.Write(String.Format("Hello {0}, I'm {1}", "Jackie", "Aillo"));
输出的结果是：Hello Jackie, I'm Aillo
二、String.Format的多格式定义：
这里所谓的多格式是指一个格式项中可以定义1~3个格式参数，每种格式参数用分号（；）隔开。带2个和3个格式参数的格式项所对应的值必须是数值类型的，这样才能判断是否为负数、正数、零。
带1个格式参数：
//以科学计数法的格式输出带2个格式参数：
double p1 = 1000000;
Response.Write(String.Format("{0:E2}", p1));
/*当格式项对应的值为非负数，则选择第一种格式；值为负数则选第二种格式*/带3个格式参数：
double p1 = 10000;
double p2 = -2420.50;
Response.Write(String.Format("{0:#,###0.00;#,###0.000;}<BR>", p1));
Response.Write(String.Format("{0:#,###0.00;#,###0.000;}", p2));
/*当格式项对应的值为正数则选择第一张格式；补充：
负数则为第二中格式；
值等于零则为第三种格式*/
1double p1 = 10000;
double p2 = -2420.50;
double p3 = 0.00;
Response.Write(String.Format("{0:#,###0.00;#,###0.000;#,###0.0000}<BR>", p1));
Response.Write(String.Format("{0:#,###0.00;#,###0.000;#,###0.0000}<BR>", p3));
Response.Write(String.Format("{0:#,###0.00;#,###0.000;#,###0.0000}", p2));
{0:N2} 中的N3,f3表示格式化之后数据的类型以及小数的位数。如：N2表示带2个小数的数字；
与此类似：
N或者n 表示 数字
F或者f 表示 固定点
E或者e 表示 科学计数法
D或者d 表示 十进制数
X或者x 表示 十六进制
G或者g 表示 常规
C或者c 表示 货币
例子：
C 或 c
货币
Console.Write("{0:C}", 2.5); //$2.50
Console.Write("{0:C}", -2.5); //($2.50)D 或 d
十进制数
Console.Write("{0:D5}", 25); //00025
E 或 e
科学型
Console.Write("{0:E}", 250000); //2.500000E+005
F 或 f
固定点
Console.Write("{0:F2}", 25); //25.00
Console.Write("{0:F0}", 25); //25
G 或 g
常规
Console.Write("{0:G}", 2.5); //2.5
N 或 n
数字
Console.Write("{0:N}", 2500000); //2,500,000.00
X 或 x
十六进制
Console.Write("{0:X}", 250); //FA
Console.Write("{0:X}", 0xffff); //FFFF原文地址：http://www.ezloo.com/2008/11/string_format.html
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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
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
x Hexadecimal {0:x4} System.
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".
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%