Why must backslashes in string literals be escaped in C++?

问题

I want to declare the same regex pattern for both languages. For TCL I do this

set pattern "\d\s\S" 

but for C++ I have to do this for the same pattern

boost::regex pattern("\\d\\s\\S");

otherwise C++ compiler will tell us the following:

warning C4129: 'd' : unrecognized character escape sequence

so why TCL don't try to find \d \s \S escape symbols and just ignores \-s but C++ tries and sucks?

P.S. PHP works as TCL as I remeber.

回答1:

This is just how C++ and PHP differ; in PHP, the character following a backslash is matched against a small set of special characters (I believe "rnvtx"). If the match fails it will just continue without altering the meaning.

However, C++ expects the character to be in that small set (I think the set is bigger btw) but if the match fails you will see an error instead.

回答2:

C++ has the concept of Character Escape Sequences. Escape sequences, which take the form \c (the 'c' being a character), are used to define certain special characters within string literals, so it follows that backslashes by themselves must also be escaped to denote that a special character isn't being implied.

来源：https://stackoverflow.com/questions/13986708/why-must-backslashes-in-string-literals-be-escaped-in-c