std::basic_...:basic_regex(3)

✨ NAME ✨

okay so bestie, this is the std::basic_regex::basic_regex page from the C++ Standard Libary (their spelling, not mine 💀), a.k.a. std::basic_...:basic_regex(3). It's literally the constructor page for std::basic_regex::basic_regex — we're building regex girlies out of character sequences, and it's giving main character energy. 🎀

🌸 Synopsis 🌸

Here's the full constructor lineup, exactly as the page has it:

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. No cap, that's the whole vibe. 💅

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.

note: the page literally skips 5) — that's not me being flaky, it's just not there 🙈

🔥 Example 🔥

Run this code, bestie:

// 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"

okay that's the whole page bestie 💖 — source http://cppreference.com, version/date 2024.06.10, page std::basic_...:basic_regex(3). go forth and construct your regexes, mwah 💅✨