C++ Cookbook

4.11. Removing a Substring from a String

Problem

You want to remove a substring from a string.

Solution

Use the find, erase, and length member functions of basic_string:

std::string t = "Banana Republic";
std::string s = "nana";

std::string::size_type i = t.find(s);

if (i != std::string::npos)
   t.erase(i, s.length());

This will erase s.length() elements starting at the index where find found the first occurrence of the substring.

Discussion

There are lots of variations on the theme of finding a substring and removing it. For example, you may want to remove all instances of a substring instead of just one. Or just the last one. Or the seventh one. Each time the steps are the same: find the index of the beginning of the pattern you want to remove, then call erase on that index for the next n characters, where n is the length of the pattern string. See Recipe 4.9 for the different member functions for finding things in strings.

Chances are you also want to make your substring-removal function generic, so you can use it on strings of any kind of character. Example 4-19 offers a generic version that removes all instances of the pattern from a string.

Example 4-19. Remove all substrings from a string (generic version)

#include <string> #include <iostream> using namespace std; template<typename T> void removeSubstrs(basic_string<T>& s, const basic_string<T>& p) { basic_string<T>::size_type n = p.length(); for (basic_string<T>::size_type i = s.find(p); i != basic_string<T>::npos; i = s.find(p)) s.erase(i, ...