This is the second part about posts what my “string_view support for regex” proposal entails. This part explains what it does for the user. part 1 explains why I started to work on it,

If my draft proposal will be accepted in C++23 it will make using std::string_view with std::regex much more pleasant experience. This post shows the most promintent features for the user’s point of view.

TL;DR

It will be possible to use a std::svmatch instead of a std::smatch to get the match results when using a std::string_view in std::regex_match or std::regex_search. The match results and its sub matches can return a std::string_view.

Regex

The std::basic_regex will get the following overloads taking a std::string_view:

• constructor
• operator=
• member function assign

Sub_match

The std::sub_match will get two new typedefs for std::string_view::const_iterator and std::wstring_view::const_iterator. They will not often be used directly by the user, but are added for completeness.

The std::sub_match class will get the following additional member functions:

• operator string_view_type() const;
• string_view_type view() const;
• int compare(string_view_type sv) const;

This allows implicit conversion to a std::string_view. Whether this will be accepted is not certain: std::sub_match can now implitely convert to both std::string and to std::string_view.

The new functions in this class make it easier to get a std::string_view of the match and do not require a std::string to look at the result.

Match_results

The std::match_result will get two new typedefs for svmatch and wvsmatch. These will be often used in user code!

The std::match_result class will get the following additional member functions:

• string_view_type view(size_type sub = 0) const;
• Two overloads of format to use a std::string_view as format argument.

The new typdefs make it easy to use a std::match_result for a std::string_view the view() function makes it easier to get a std::string_view of the match and do not require a std::string to look at the result.

Regex_match & regex_search

The std::regex_match and std::regex_search functions get overloads to take a std::string_view as input.

regex_replace

The std::regex_replace function get overloads to take a std::string_view as input and format argument.

Hidden goodies

There are some more hidden goodies in the proposal. Most constructions of temporary std::string objects will become temporary std::string_view objects. The latter is much cheaper to create and consumes less memory. There are several other typedefs using a std::string_view, but will probably not be used a lot.

Caveat emptor

Another tiny issue with std::sub_match is the fact it takes BidirectionalIterator which does not need to be continious. For most code the BidirectionalIterator will also be continuous, for example:

• const char *
• std::string
• std::string_view
• std::vector
• std::array

But the following types are not continuos:

• std::deque
• std::list

In these cases the std::string_view operator will not be available and the view() member returns the same as str().

The latest draft of the proposal contains all details. Hopefully this will become part of C++23.