In C++, get consecutive substring count in a string

My assignment requires that I count all occurrences of a substring within a string and return the count. The tricky part is that I need to count the longest consecutive occurrence of the substrings, not just the overall amount of times they are in the string. For example: substring = "abc" string = "abcabcabcabcdefghabc", in this I would need it to return 4 because the longest consecutive repetition is 4. The method declaration I have been using is:

int GetCount (std::string substring, std::string str);

If I could get help with the definition I would really appreciate it.