C ++中的正则表达式，用于接受“ \\”

Question

I am trying to use C++ library to use regex expression .

bool x =   std::regex_match(cInputLayoutRec->InputString, std::regex("^[A-Z0-9-\'// ]*$"));

in this case the result should be true (x) if the input supplied is any of these letters A to Z , 0-9 , \\ , ' AND /

Its working for all the conditions except \\ ie if the input string contains \\ this results into false. I tried with putting /\\ to cater for this special character '\\' even then its not working.
Can anyone suggest some inputs if i am missing something ?

Thanks in Advance!

Answer 1

其他答案是正确的，但是由于您使用的是C ++ 11，因此应注意，您也可以使用原始字符串文字，如下所示：

std::regex(R"(^[A-Z0-9-\\'// ]*$)")

Answer 2

You are using \\ in a string, hence it will treated as a string escape sequence (in your case escaping ' .

You need to use \\\\ to have a \\ in a string.

As the backslash is also an escape character for regexes, you have to escape this again, so use \\\\\\\\ to represent the \\ character in a regex.

Answer 3

The \\ character is used for escaping pretty much everywhere. This "everywhere" includes C++ string literals syntax and regex syntax.

Your regex definition in C++ should be:

std::regex("^[A-Z0-9-\\\\'// ]*$") 

This is what happens:

• C++ parser interprets the string literal "^[A-Z0-9-\\\\\\\\'// ]*$" as the string with the following contents: ^[A-Z0-9-\\\\'// ]*$ . This string is passed to the regex parser. Note that two sequences \\\\ have been "replaced" with \\ .

• Regex parser interprets the \\\\ sequence as literal \\ character in your character class.