.NET字符串格式化 - 小数点左边的＃是什么意思？(.NET String formatting -What does the # mean to the left of the decimal point?)

 我需要将数字字符串格式化为小数点两边最多2个位置，即使这意味着截断或截断前导数字（这是一个很长的故事，不要问）。 在MSDN上，它暗示可以使用井号（＃）完成： 
 
 
 
 “”＃“自定义格式说明符用作数字占位符符号。如果格式化的值在格式字符串中出现井号的位置有一个数字，则该数字将复制到结果字符串。否则，没有任何东西存储在结果字符串中的那个位置。“ 
 
 
 但在实践中，似乎只能在小数点右侧工作。 如果我这样做： 
 
String s = " Test - " + String.Format("format0 = {0:0.##}, format1 = {1:#.##}, format2 = {2:##.###}",321.2345, 321.2345, 321.2345);
 
 我得到s的这个输出： 
 
 
 
 “测试 - 格式0 = 321.23，格式1 = 321.23，格式2 = 321.235” 
 
 
 ...注意“0。##”和“＃。##”产生相同的输出。 那么当它位于小数点左侧时，“＃” 究竟是什么意思呢？ 

I have a need to format a numeric string to a maximum of 2 places either side of the decimal point, even if it means truncating or chopping off the leading digits (it's a long story, don't ask). On the MSDN it implies this can be done with the pound sign (#):
 
 
 
"The "#" custom format specifier serves as a digit-placeholder symbol. If the value that is being formatted has a digit in the position where the pound sign appears in the format string, that digit is copied to the result string. Otherwise, nothing is stored in that position in the result string."
 
 
But in practice that only seems to work to the right of the decimal point. If I do this:
 
String s = " Test - " + String.Format("format0 = {0:0.##}, format1 = {1:#.##}, format2 = {2:##.###}",321.2345, 321.2345, 321.2345);
 
I get this output for s:
 
 
 
" Test - format0 = 321.23, format1 = 321.23, format2 = 321.235"
 
 
... note that "0.##" and "#.##" produced the same output. So what exactly does the "#" mean when it's to the left of the decimal point? 

原文：https://stackoverflow.com/questions/20707973