迭代器错误C2440

Question

I am trying to make a small hashing program but there is an error I don't know how to deal with. The problem is on the arrow and here is the error:

Error 1 error C2440: 'initializing' : cannot convert from 'std::_String_const_iterator<_Elem,_Traits,_Alloc>' to 'std::_String_iterator<_Elem,_Traits,_Alloc>'

My code:

#include <iostream>
#include <string>
#include <iterator>
using namespace std;

unsigned long hash(const string& str);

int main()
{
   long out;
   string word;
   word = "about";
   out = hash(word) % 255;
   cout << out;
   system("pause");
   return 0;
}


unsigned long djb2(const string& str)
{
    unsigned long hash = 5381;

    for(string::iterator it=str.begin();it!=str.end();it++)  //<~~~~~~~~~~
        hash = ((hash << 5) + hash) + *it; /* hash * 33 + character */

    return hash;
 }

Answer 1

You need to use a const_iterator :

 for( std::string::const_iterator it=str.begin();it!=str.end();it++)

since your argument to the function is const string &str the iterator has to agree.