NAME¶

std::basic_regex::basic_regex - std::basic_regex::basic_regex

Synopsis¶

basic_regex(); (1) (since C++11)
explicit basic_regex( const CharT* s,
flag_type f = (2) (since C++11)
std::regex_constants::ECMAScript );
basic_regex( const CharT* s, std::size_t count, (3) (since C++11)
flag_type f = std::regex_constants::ECMAScript );
basic_regex( const basic_regex& other ); (4) (since C++11)
basic_regex( basic_regex&& other ) noexcept; (5) (since C++11)
template< class ST, class SA >

explicit basic_regex( const std::basic_string<CharT,ST,SA>& str, (6) (since C++11)

flag_type f =
std::regex_constants::ECMAScript );
template< class ForwardIt >

basic_regex( ForwardIt first, ForwardIt last, (7) (since C++11)

flag_type f = std::regex_constants::ECMAScript );
basic_regex( std::initializer_list<CharT> init, (8) (since C++11)
flag_type f = std::regex_constants::ECMAScript );

Constructs a new regular expression from a sequence of characters interpreted
according to the flags f.

1) Default constructor. Constructs an empty regular expression which will match
nothing.
2) Constructs a regex from a null-terminated string s.
3) Constructs a regex from a sequence of count characters, pointed to by s.
4) Copy constructor. Constructs a regex by copying other.
5) Move constructor. Constructs a regex with the contents of other using move
semantics.
6) Constructs a regex from a string str.
7) Range constructor. Constructs the string with the contents of the range
[first, last).
8) Initializer list constructor. Constructs the string with the contents of the
initializer list init.

Parameters¶

s - pointer to a null-terminated string
count - length of a character sequence used to initialize the regex
first, last - range of a character sequence used to initialize the regex
str - a basic_string used as a source used to initialize the regex
other - another regex to use as source to initialize the regex
init - initializer list used to initialize the regex
f - flags used to guide the interpretation of the character sequence as a
regular expression

Type requirements¶

-
ForwardIt must meet the requirements of LegacyForwardIterator.

Exceptions¶

1) May throw implementation-defined exceptions.
2,3) std::regex_error if the supplied regular expression is not valid.
4) May throw implementation-defined exceptions.
6-8) std::regex_error if the supplied regular expression is not valid.

Example¶

// Run this code

#include <iomanip>
#include <iostream>
#include <regex>
#include <string>

void match_and_print(const std::string& text, const std::regex& pattern)
{
std::sregex_iterator it(text.begin(), text.end(), pattern), it_end;
int count = 0;
for (; it != it_end; ++it)
{
const std::smatch& match = *it;
std::cout << ++count << ". " << std::quoted(match.str()) << '\n';
}
std::cout << (count ? "\n" : "no match found\n\n");
}

int main()
{
const std::string text = "Hello, World! 12345";

// Matches one or more digits
std::string pattern_text = "\\d+";
std::cout << "digits (" << pattern_text << "):\n";
auto pattern = std::regex(pattern_text);
match_and_print(text, pattern);

// Matches one or more characters split by space
pattern_text = "[^\\s]+";
std::cout << "words (" << pattern_text << "):\n";
pattern = std::regex(pattern_text);
match_and_print(text, pattern);

// Matches one or more characters split by space
pattern_text = "[a-zA-Z]+";
std::cout << "words without symbols and digits (" << pattern_text << "):\n";
pattern = std::regex(pattern_text);
match_and_print(text, pattern);

// Matches one non digits, non alphabet
pattern_text = "[^0-9A-Za-z]";
std::cout << "symbol (" << pattern_text << "):\n";
pattern = std::regex(pattern_text);
match_and_print(text, pattern);

// Matches one or more lowercase
pattern_text = "[a-z]+";
std::cout << "lowercase (" << pattern_text << "):\n";
pattern = std::regex(pattern_text);
match_and_print(text, pattern);

// Matches one or more lowercase with std::regex::icase flag
pattern_text = "[a-z]+";
std::cout << "lowercase with ignore case flag (" << pattern_text << "):\n";
pattern = std::regex(pattern_text, std::regex::icase);
match_and_print(text, pattern);

// Matches basic POSIX regular expression
pattern_text = "[[:digit:]]+";
std::cout << "basic POSIX regex (" << pattern_text << "):\n";
pattern = std::regex(pattern_text, std::regex::basic);
match_and_print(text, pattern);

// Matches extended POSIX regular expression
pattern_text = "[[:digit:]]+";
std::cout << "extended POSIX regex (" << pattern_text << "):\n";
pattern = std::regex(pattern_text, std::regex::extended);
match_and_print(text, pattern);
}

Output:¶

digits (\d+):
1. "12345"

words ([^\s]+):
1. "Hello,"
2. "World!"
3. "12345"

words without symbols and digits ([a-zA-Z]+):
1. "Hello"
2. "World"

symbol ([^0-9A-Za-z]):
1. ","
2. " "
3. "!"
4. " "

lowercase ([a-z]+):
1. "ello"
2. "orld"

lowercase with ignore case flag ([a-z]+):
1. "Hello"
2. "World"

basic POSIX regex ([[:digit:]]+):
no match found

extended POSIX regex ([[:digit:]]+):
1. "12345"