В тексте заменить слово А(любое слово) на слово В(любое слово). А и В разной длинны

#include <iostream>
#include <string>
 
size_t find_any_first_of(std::string const& source, std::string const& item, size_t start = 0)
{
    size_t pos = std::string::npos;
 
    for (size_t i = 0; i < item.length(); ++i)
    {
        size_t p = source.find_first_of(item.at(i), start);
        if (pos > p)
        {
            pos = p;
            if (pos == start) break;
        }
    }
 
    return pos;
}
 
size_t find_any_first_not_of(std::string const& source, std::string const& item, size_t start = 0)
{
    size_t pos = std::string::npos;
 
    for (size_t p = start; p < source.length(); ++p)
    {
        bool no_item = true;
        for (size_t i = 0; i < item.length(); ++i)
        {
            if (source.at(p) == item.at(i))
            {
                no_item = false;
                break;
            }
        }
        if (no_item)
        {
            pos = p;
            break;
        }
    }
 
    return pos;
}
 
size_t replace_all_of(std::string& source, std::string const& replacing, std::string const& replacer, std::string const& delimiter = " ")
{
    size_t count = 0;
 
    size_t p1 = 0;
    size_t p2 = 0;
    while ((p1 = find_any_first_not_of(source, delimiter, p1)) != std::string::npos)
    {
        p2 = find_any_first_of(source, delimiter, p1 + 1);
        if (p2 == std::string::npos) p2 = source.length();
        size_t len = p2 - p1;
        if (source.compare(p1, len, replacing) == 0)
        {
            source.replace(p1, len, replacer);
            p1 += replacer.length();
            ++count;
        }
        else
        {
            p1 = p2 + 1;
        }
    }
 
    return count;
}
 
int main()
{
    using namespace std;
 
    string delimiter = " \t,.!?"; // Необходимые разделители можно добавить.
 
    string sentence = "\tgreen apple is not red apple still, \"green\" apple is an apple, and \"red\" apple is also an apple therefore, both are apples!";
    //cout << "Input sentence: ";
    //getline(cin, sentence);
 
    string replacing = "green";
    //cout << "Input replacing word: ";
    //cin >> replacing;
 
    string replacer = "yellow";
    //cout << "Input replacer word: ";
    //cin >> replacer;
 
    cout << "Sentence: " << sentence << endl;
    cout << "Replacing: " << replacing << endl;
    cout << "Replacer: " << replacer << endl;
    cout << "Replace " << replace_all_of(sentence, replacing, replacer, delimiter) << endl;
    cout << "Result: " << sentence << endl;
 
    return 0;
}