Regex C++ Note

Below is my summary note over regular expression (regex) library as provided in C++ standard.

Generic Objects

These are generic type in which there are specialized type (noted as _{(specialized)} in subsequent sections below) users will directly work with.

STL Names	Note
`std::basic_regex`	Holds regex string used in regular expression operation. By default it’s created by using ECMAScript syntax. It provides with quite options to choose from namely `basic`, `extended`, `awk`, `grep`, `egrep`, and `ECMAScript`.
`std::sub_match`	We don’t use it directly, but used by regex engine itself to mark and denote the sequences of characters matched by input regex string.
`std::match_results`	Matching results which we directly work with. It holds a collection of `std::sub_match` as result we can make use of. It provides more meta information like `prefix`, `suffix`, `size` of matching result, and random access to each matching result for convenient in iterating through the collection.

Operations

STL Names	Note
`std::regex_match`	Process the input string to determine whether it matches the entire target character sequence.
`std::regex_search`	Process the input string to determine whether it matches some of the subsequence character sequence.
`std::regex_replace`	Perform replacing the target input string according to regex string.

Regex String _{(specialized)}

All of these are typedef-ed from std::basic_regex with different types.

STL Names	Note
`std::regex`	It’s typedef-ed from `typedef basic_regex<char> regex;` Basically works with ASCII character type.
`std::wregex`	It’s typedef-ed from `typedef basic_regex<wchar_t> regex;` Basically works with wide-character (character that needs multiple bytes to represent i.e. CJK charcter etc).

Matching Results _{(specialized)}

All of these are typedef-ed from std::match_results with different types.

STL Names	Note
`std::cmatch`	It’s typedef-ed from `typedef match_results<const char*> cmatch;` Basically works with C-style string of ASCII type.
`std::smatch`	It’s typedef-ed from `typedef match_results<string::const_iterator> smatch;` Basically works with C++ - style string. Use `const_iterator` to provide features from `std::iterator`.
`std::wcmatch`	It’s typedef-ed from `typedef match_results<const wchar_t*> wcmatch;` Basically works with C-style string of wide-character type `wchar_t`.
`std::wsmatch`	It’s typedef-ed from `typedef match_results<wstring::const_iterator> wsmatch;` Basically works with C++ - style string of wide-character type. Use `const_iterator` to provide features from `std::iterator`.

Sub-matching Result _{(specialized)}

All of these are typedef-ed from std::sub_match with different types.

STL Names	Note
`std::csub_match`	It’s typedef-ed from `typedef sub_match<const char*> csub_match;` Basically works with C-style string of ASCII type.
`std::ssub_match`	It’s typedef-ed from `typedef sub_match<string::const_iterator> ssub_match;` Basically works with C++ - style string. Use `const_iterator` to provide features from `std::iterator`.
`std::wcsub_match`	It’s typedef-ed from `typedef sub_match<const wchar_t*> wcsub_match;` Basically works with C-style string of wide-character type `wchar_t`.
`std::wssub_match`	It’s typedef-ed from `typedef sub_match<wstring::const_iterator> wssub_match;` Basically works with C++ - style string of wide-character type. Use `const_iterator` to provide features from `std::iterator`.

Code Examples

I’ve done demonstration code in using regex. Each topic focuses on Operations which in itself covers usage of basic building-block of working with regex in C++ namely

std::regex for regex string
std::regex_... for operations i.e. std::regex_match, std::regex_search, and std::regex_replace
std::match_results for matching results

Topic	URL
`std::regex_match`	Regex_RegexMatch.cpp
`std::regex_search`	Regex_RegexSearch.cpp
`std::regex_replace`	Regex_RegexReplace.cpp
`Attribute Parser - Hackerrank Problem`	AttributeParser.cpp

Update

Nov, 15, 2019

Fixed typo, and add info telling where sub-matching result typedef-ed from.

First published on Oct, 8, 2019

Written by Wasin Thonkaew
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