Detail the C++ standard library class std::regex that deals with regular expressions

std is the namespace of the C++ standard library and contains a large number of standard C++ classes, functions, and objects. These classes and functions provide a wide range of functionality, including input and output, containers, algorithms, string handling, and more.

Usually, to use objects and functions from the standard library, you include the appropriate header file in your code, such as #include . You can then use the std:: prefix, such as std::cout, std::cin, std::endl, etc.

This usage helps prevent naming conflicts, since multiple libraries in C++ may provide the same name. Using namespaces makes it clear that you want to use a feature in the standard library rather than a feature of the same name defined elsewhere.

Common classes and functions in the C++ standard library:

1. Class: - 'std::string' :string processing class. - 'std::vector' : dynamic array container class. - 'std::map', 'std::unordered_map' : key-value pair mapping container class. - 'std::fstream' : file input/output class. - 'std::deque' : double-ended queue container class. - 'std::set', 'std::unordered_set' : collection container class. - 'std::stack', 'std::queue' :stack and queue container adapter class. - 'std::stringstream' :stringstream class.

2. Functions: - 'std::cout', 'std::cerr' : console output function. - 'std::cin' : console input function. - 'std::sort' : container sorting function. - 'std::find' : container search function. - 'std::max', 'std::min' : Returns the greater or lesser of the two values. - 'std::accumulate' : container element summation function. - 'std::copy' : copies a range element to another range function. - 'std::transform' : container element conversion function. - 'std::regex_search' : regular expression search function. - 'std::regex_match' : indicates the regular expression matching function. - 'std::regex_replace' : regular expression replacement function.

3. Object: - 'std::endl' : Wrap and refresh the output stream object. - 'std::numeric_limits' : indicates the value type limit information object. - 'std::allocator' : dynamic memory allocator object. - 'std::cin.eof()' : Input stream object function to check whether the end of the file is reached. - 'std::nothrow' : An object that returns a null pointer without throwing an exception when memory allocation fails. - 'std::random_device' : truly random number generation object. - 'std::locale' : Object that controls the localization behavior of the C++ standard library.

These classes, functions, and objects provide a wealth of functionality covering input and output, containers, algorithms, string processing, regular expressions, and more, providing C++ programmers with powerful tools for various types of application development.

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'std::regex' is a class provided in the C++ standard library for handling regular expressions. Regular expressions are a powerful pattern matching tool, which can be used to perform complex search and replace operations in strings. The std::regex class provides a way to create, compile, and use regular expressions.

Here are some important member functions and uses of the 'std::regex' class:

1. Constructor: - `explicit regex(const char* fmt, flag_type flags = std::regex_constants::ECMAScript)` - `explicit regex(const std::string& fmt, flag_type flags = std::regex_constants::ECMAScript) 'These constructors are used to create a' std::regex 'object that takes a regular expression string as an argument and optionally specifies matching flags.

2. Member functions' match() 'and' search() ': - `bool match(const std::string& s, std::regex_constants::match_flag_type flags = std::regex_constants::match_default) const` - `bool search(const std::string& s, std::regex_constants::match_flag_type flags = std::regex_constants::match_default) const` These two member functions are used to perform a full match(' match() ') and a partial match(' search() ') in a string, respectively. They accept a string to be matched as an argument and optionally specify a matching flag.

3. Replacement function 'std::regex_replace()' : - `std::string regex_replace(InputIt first, InputIt last, const std::regex& re, const std::string& fmt, std::regex_constants::match_flag_type flags = std::regex_constants::match_default)`

This function is used to search for and replace parts of the range '[first, last)' that satisfy the regular expression 're'. The replacement method is specified by the parameter 'fmt'.

4. Regular expression syntax: 'std::regex' supports a variety of regular expression syntax, including ECMAScript, basic, extended and so on. You can specify the syntax to use by setting different flags. Common flags include: - 'std::regex_constants::ECMAScript' : Use ECMAScript syntax. - 'std::regex_constants::basic' : Uses basic regular expression syntax. - 'std::regex_constants::extended' : Uses extended regular expression syntax.

These are just some of the common member functions and uses of the 'std::regex' class. With the help of these functions, regular expressions can be easily searched and replaced in strings, and complex text processing functions can be realized.

#include <iostream> #include <regex> #include <string> int main() {// Raw string std::string text = "Hello, world!" ; // Define a regular expression pattern std::regex pattern("world"); if (std::regex_search(text, pattern)) {std::cout << "Found a matching pattern in the text!" << std::endl; } else {std::cout << "No matching pattern found!" << std::endl; } return 0; }

/*std::regex: indicates a regular expression object. std::smatch: A container that holds match results, which can be filled with the std::regex_match or std::regex_search functions. std::regex_match: Used to check whether the entire string matches the regular expression. std::regex_search: Searches the input string for matches with the regular expression. std::regex_replace: Used to perform regular expression replacements in strings. std::regex_iterator: Used to iterate over all substrings in a string that match the regular expression. std::regex_token_iterator: Used to iterate over substrings in a string that match regular expressions and their non-matching parts. * /

#include <iostream> #include <regex> int main() { std::string text = "Hello, my email is example@email.com and my phone number is 123-456-7890."; std::regex emailRegex("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}"); std::regex phoneRegex("\\d{3}-\\d{3}-\\d{4}"); // Match email std::smatch emailMatch; if (std::regex_search(text, emailMatch, emailRegex)) { std::cout << "Email found: " << emailMatch.str() << std::endl; } // Match phone number std::smatch phoneMatch; if (std::regex_search(text, phoneMatch, phoneRegex)) { std::cout << "Phone number found: " << phoneMatch.str() << std::endl; } // Replace phone number std::string newText = std::regex_replace(text, phoneRegex, "XXX-XXX-XXXX"); std::cout << "Text with phone number replaced: " << newText << std::endl; return 0; } /*std::regex: Represents a regular expression object. std::smatch: A container that holds match results, which can be filled with the std::regex_match or std::regex_search functions. std::regex_match: Used to check whether the entire string matches the regular expression. std::regex_search: Searches the input string for matches with the regular expression. std::regex_replace: Used to perform regular expression replacements in strings. std::regex_iterator: Used to iterate over all substrings in a string that match the regular expression. std::regex_token_iterator: Used to iterate over substrings in a string that match regular expressions and their non-matching parts. * /

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