Question

is there any STL algorithm or a standard way of finding how many occurences of particular substring are there in a string? For example in string:

'How do you do at ou'

the string “ou” appears twice. I tried some STL algorithms with and without predicates but what I found is that those algorithms from STL want to compare components of string which in my case is char but cannot? compare substrings.
I come up with something like this:

str – string

obj – substring we’re looking for

std::string::size_type count_subs(const std::string& str, const std::string& obj)
{
std::string::const_iterator beg = str.begin();
std::string::const_iterator end = str.end();
std::string::size_type count = 0;
while ((beg + (obj.size() - 1)) != end)
{
    std::string tmp(beg, beg + obj.size());
    if (tmp == obj)
    {
        ++count;
    }
    ++beg;
}
return count;
}

thank you.

Answer 1

#include <string>
#include <iostream>

int Count( const std::string & str, 
           const std::string & obj ) {
    int n = 0;
    std::string ::size_type pos = 0;
    while( (pos = obj.find( str, pos )) 
                 != std::string::npos ) {
        n++;
        pos += str.size();
    }
    return n;
}

int main() {
    std::string s = "How do you do at ou";
    int n = Count( "ou", s );
    std::cout << n << std::endl;
}