神秘的字符串进行双重转换

Question

I am tying to convert a string to double in C#, wherein i face a situation,

String of value "6,," gets converted to double whereas the string "6++" or a number with successive chars throws an error which is understandable.

Please clarify why the first string gets converted?

Answer 1

The comma is used as a thousands separator in some cultures, so it's acceptable for it to be present in a numeric string. The same cannot be said for a plus sign.

To clarify, "+6" would be valid, since you can represent a positive number explicitly with the plus sign. However, "6+" is not a recognised numeric format in any culture that I am aware of. Similarly, while "6," could be considered valid, ",6" probably isn't unless you specifically use a culture where the comma is a decimal separator.

Answer 2

Since , is the thousands separator for the invariant culture, the parser just ignores them before the decimal point. You can also parse "6,4,55.23" and it yields 6455.23 .

Trying to parse a number with a comma after the decimal point, however, results in an error.

In the documentation doe Double.Parse , the following rules are given (paraphrased):

[ws][sign][integral-digits[,]]integral-digits[.[fractional-digits]][E[sign]exponential-digits][ws]

• Runs of integral-digits can be partitioned by a group-separator symbol. For example, in some cultures a comma (,) separates groups of thousands

So there's no requirement that the thousands separator have three digits after it (or between consecutive separators)