Найти самое длинное слово в строке

#include "stdafx.h"
#include <string>
#include <vector>
#include <iostream>
#include <algorithm>
#include <iterator>
 
 
std::string FindMaxWord(std::string str) 
{
    size_t max = 0;
    auto result = std::find_if(str.rbegin(), str.rend(), isspace(str));
    if (result != str.rend())
        max = strlen(result);
    return result;  
}
 
 
int main()
{
    std::string lines = { "There are many big and small libraries everywhere in our country" };
    std::cout << "FindMaxWord: " << FindMaxWord(lines) << "\n";
}

#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <iterator>
 
bool lengthComparer(const std::string &s1, const std::string &s2)
{
    return s1.size() < s2.size();
}
 
int main()
{
    std::string lines = { "There are many big and small libraries everywhere in our country" };
    std::istringstream in(lines);
    std::istream_iterator<std::string> in_begin(in), in_end;
    std::string max_length_word = *max_element(in_begin, in_end, lengthComparer);
    std::cout << "Max length word: " << max_length_word << "\n";
}

#include <sstream>
#include <string>
#include <iostream>
  
int main()
{
    std::string lines = { "There are many big and small libraries everywhere in our country" };
    std::stringstream ss(lines);
    std::string max;
    while (ss >> lines)
        if (lines.size() > max.size())
            max = lines;
    
    std::cout << max << std::endl;
}

#include <iostream>
#include <string>
#include <algorithm>
 
bool is_alpha(char c) { return ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')); }
bool is_not_alpha(char c){ return !is_alpha(c); }
 
bool max_word(std::string& w, const std::string& s){
    size_t n, m = 0;
    std::string::const_iterator j, i = s.begin(), p = s.end();
    while((i = std::find_if(i, s.end(), is_alpha)) != s.end()){
        j = std::find_if(i, s.end(), is_not_alpha);
        n = static_cast<size_t>(j - i);
        if(n > m){
            m = n;
            p = i;
        }
        i = j;
    }
    
    w = "";
    if(p != s.end())
        w.assign(p, p + m);
    return (w.length() > 0);
}
 
int main(void){
    std::string s = "lisp, forth, pascal";
 
    std::string w;
    if(max_word(w, s))
        std::cout << "max word: " << w << std::endl;
    std::cin.get();
    return 0;
}