Explore the full potential of C++ by mastering the standard library.

Become a C++ Programmer

The C++ standard library is a collection of all the tools and utilities available in C++. It received its latest update in 2017, known as C++17. The update introduces many new features that further optimize our code. This module will help us fully grasp C++ and use it to its full potential.

C++ Standard Library

`std::regex_replace` and `std::match_results.format` in combination with capture groups enables you to format text. You can use a format string together with a placeholder to insert the value. 

Here are both possibilities:

#include <regex>
 
#include <iomanip>
#include <iostream>
#include <string>
 
int main(){
 
  std::cout << std::endl;
 
  std::string future{"Future"};
  int len= sizeof(future);
 
  const std::string unofficial{"unofficial, C++0x"};
  const std::string official{"official, C++11"};
 
  std::regex regValues{"(.*), (.*)"};
 
 
  std::string standardText{"The $1 name of the new C++ standard is $2."};
 
  // using std::regex_replace
  std::string textNow= std::regex_replace(unofficial, regValues, standardText );
 
  std::cout <<  std::setw(len) << std::left << "Now: " << textNow << std::endl;
 
  // using std::match_results
  // typedef match_results<string::const_iterator> smatch;
  std::smatch smatch;
  if ( std::regex_match(official, smatch, regValues)){
 
    std::string textFuture= smatch.format(standardText);
    std::cout <<  std::setw(len) << std::left << "Future: " << textFuture << std::endl;
 
  }
 
  std::cout << std::endl;
 
}

cpp17.tar.gz

c++17

C++17N

adaptor

In the function call `std::regex_replace(unoffical, regValues, standardText)` the text matching the first and second capture group of the regular expression `regValues` is extracted from the string `unofficial`. The placeholders `＄1` and `＄2` in the text `standardText` are then replaced by the extracted values. The strategy of `smatch.format(standardText)` is similar but there is a difference: 

The creation of the search results `smatch` is separated from their usage when formatting the string. 

In addition to capture groups, C++ supports additional format escape sequences. You can use them in format strings:



| **Format escape sequence** | **Description** | 
|-|-|
| `＄&` | Returns the total match (0th capture group). |
| `＄＄` | Returns $. |
| ``＄` `` (backward tic) | Returns the text before the total match. |
| ``＄´`` (forward tic) | Returns the text after the total match. |
| `＄i` | Returns the ith capture group. |
<p> <strong> Format escape sequences  </strong> </p>



Regular expressions can also specify the format of the target text. Find the implementation below.