Regular Expressions
Regular expressions are a standardized way to express patterns to be matched against sequences of characters.

The standard C++ library provides support for regular expressions in the <regex> header through a series of operations. All these operations make use of some typical regex parameters:
  • Target sequence (subject): The sequence of characters searched for the pattern. Generally, this is a range specified by two iterators, but some functions also accept a c-string or a string object instead.
  • Regular expression (pattern): The pattern which is searched for in the target sequence. This must be an object of a basic_regex type (such as regex), generally constructed from a string with a special syntax that describes what constitutes a match (see ECMAScript syntax).
  • Matches array: Some operations allow to retrieve information about matches. This information is stored in one of the special match_results array types (such as cmatch or smatch).
  • Replacement string: Some operations can replace matches. These replacements are specified in strings that allow for a special format (see ECMAScript syntax).

Regex operations

Regex operations are performed using either functions or special iterator adaptors:


Iterator types:


The regex functions and iterators make heavy use of a set of supporting types as arguments and return values:

Basic types:

Some of these types are templates, and have aliases for their most common instantiations:

basic_regex instantiations:

match_results instantiations:

sub_match instantiations:


This header also defines a namespace, regex_constants, under which all constant values to be used by the library are located:


Regular expressions follow very strict grammars. By default, the functions in this library use the ECMAScript grammar:

Other functions