C++ Boost String Algorithms Library

The Boost String Algorithms Library provides a generic implementation of string-related algorithms which are missing in STL. It is an extension to the algorithms library of STL and it includes trimming, case conversion, predicates and find/replace functions. All of them come in different variants so it is easier to choose the best fit for a particular need.

The implementation is not restricted to work with a particular container (like basic_string), rather it is as generic as possible. This generalization is not compromising the performance since algorithms are using container specific features when it means a performance gain.

• Converting a string to uppercase and lowercase.

  STL has a nice way of converting the character case. Unfortunately, it works only for a single character and we want to convert a string,

  • to_upper() and to_lower() convert the case of characters in a string using a specified locale.
  • to_upper_copy() and to_lower_copy() returns the copy of the converted string.

  Examples:

  #include <boost/algorithm/string.hpp>
  #include <iostream>
  
  using namespace std;
  using namespace boost::algorithm;
  
  int main()
  {
      string str("Hello");
      string upper_s;
      string lower_s;
  
      cout << "Actual string: "
           << str << endl;
  
      to_upper(str);
      cout << "Actual string converted to uppercase: "
           << str << endl;
  
      to_lower(str);
      cout << "Actual string converted to lowercase: "
           << str << endl;
  
      str = "Hello";
      upper_s = to_upper_copy(str);
      lower_s = to_lower_copy(str);
  
      cout << "Converted Uppercase string: "
           << upper_s << endl;
      cout << "Converted Lowercase string: "
           << lower_s << endl;
  
      return 0;
  }
  Output:
  
  

  Actual string: Hello
  Actual string converted to uppercase: HELLO
  Actual string converted to lowercase: hello
  Converted Uppercase string: HELLO
  Converted Lowercase string: hello
  

• To remove characters from a string

  Boost.StringAlgorithms provides several functions you can use to delete individual characters from a string.

  • erase_first_copy() will remove the first occurrence in the source string.
  • erase_nth_copy() will remove the nth occurrence in the source string.
  • erase_all_copy() will remove all occurrences of a particular character from a string.
  • To shorten a string by a specific number of characters on either end, use the functions erase_head_copy() and erase_tail_copy().

  Example

  #include <boost/algorithm/string.hpp>
  #include <cstdlib>
  #include <iostream>
  #include <string>
  
  using namespace std;
  using namespace boost::algorithm;
  
  int main()
  {
  
      string s = "geeksforgeeks";
      cout << erase_first_copy(s, "g") << '\n';
      cout << erase_nth_copy(s, "g", 0) << '\n';
      cout << erase_last_copy(s, "g") << '\n';
      cout << erase_all_copy(s, "g") << '\n';
      cout << erase_head_copy(s, 5) << '\n';
      cout << erase_tail_copy(s, 1) << '\n';
      return 0;
  }
  Output:

  eeksforgeeks
  eeksforgeeks
  geeksforeeks
  eeksforeeks
  forgeeks
  geeksforgeek
  

• To replace characters from a string

  Boost.StringAlgorithms provides several functions you can use to replace individual characters from a string.

  • replace_first_copy() will replace the first occurrence in the source string.
  • replace_nth_copy() will replace the nth occurrence in the source string.
  • replace_all_copy() will replace all occurrences of a particular character from a string.

  Example

  #include <boost/algorithm/string.hpp>
  #include <cstdlib>
  #include <iostream>
  #include <string>
  
  using namespace std;
  using namespace boost::algorithm;
  
  int main()
  {
  
      string s = "geeks_for_geeks";
      cout
          << replace_first_copy(s, "_", "-")
          << '\n';
      cout
          << replace_last_copy(s, "_", "-")
          << '\n';
      cout
          << replace_all_copy(s, "_", "-")
          << '\n';
      return 0;
  }
  Output:

  geeks-for_geeks
  geeks_for-geeks
  geeks-for-geeks
  

Reference: https://www.boost.org/doc/libs/1_70_0/doc/html/string_algo/reference.html