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C++ Boost String Algorithms Library
  • Last Updated : 03 Jun, 2019

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:

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    #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;
    }

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    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

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    #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;
    }

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    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

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    #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;
    }

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    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

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