Find all occurrences of a substring in a string in C++

This post will discuss how to find all occurrences of a substring in a string in C++.

1. Using `string::find`

The standard approach to find the index of a substring in a string is with the string::find member function. If the substring doesn’t occur in the string, the function returns string::npos. To find all occurrences of a substring in a string, we can repeatedly call the string::find function within a loop, where the search for the next substring starts with the index of the previous match.

#include <iostream>

#include <string>

int main()

{

std::string s = "A,B,C,";

std::string substr = ",";

int index = 0;

while ((index = s.find(substr, index)) != std::string::npos) {

std::cout << index << std::endl;

index += substr.length();

}

return 0;

}

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Output:

1
3
5

2. Using Boost

Another option is to use the C++ boost library to find all occurrences of the search string in the input. The following solution demonstrates this using the boost::find_all algorithm from the header <boost/algorithm/string/split.hpp>.

#include <iostream>

#include <string>

#include <boost/algorithm/string.hpp>

int main()

{

std::string s = "A,B,C,";

std::string substr = ",";

std::vector<boost::iterator_range<std::string::const_iterator>> matches;

boost::find_all(matches, s, substr);

for (auto match : matches) {

int index = match.begin() - s.begin();

std::cout << index << std::endl;

}

return 0;

}

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Output:

1
3
5

That’s all about finding all occurrences of a substring in a string in C++.

Find all occurrences of a substring in a string in C++

1. Using string::find

2. Using Boost

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1. Using `string::find`