c++11/regex - search for exact string, escape [duplicate]

Question

Say you have a string which is provided by the user. It can contain any kind of character. Examples are:

std::string s1{"hello world");
std::string s1{".*");
std::string s1{"*{}97(}{.}}\\testing___just a --%#$%# literal%$#%^"};
...

Now I want to search in some text for occurrences of >> followed by the input string s1 followed by <<. For this, I have the following code:

std::string input; // the input text
std::regex regex{">> " + s1 + " <<"};

if (std::regex_match(input, regex)) {
     // add logic here
}

This works fine if s1 did not contain any special characters. However, if s1 had some special characters, which are recognized by the regex engine, it doesn't work.

How can I escape s1 such that std::regex considers it as a literal, and therefore does not interpret s1? In other words, the regex should be:

std::regex regex{">> " + ESCAPE(s1) + " <<"};

Is there a function like ESCAPE() in std?

important I simplified my question. In my real case, the regex is much more complex. As I am only having troubles with the fact the s1 is interpreted, I left these details out.

Answer 1

You will have to escape all special characters in the string with \. The most straightforward approach would be to use another expression to sanitize the input string before creating the expression regex.

// matches any characters that need to be escaped in RegEx
std::regex specialChars { R"([-[\]{}()*+?.,\^$|#\s])" };

std::string input = ">> "+ s1 +" <<"; 
std::string sanitized = std::regex_replace( input, specialChars, R"(\$&)" );

// "sanitized" can now safely be used in another expression