const error

I'm working with a standard container and it keeps getting a compile error about discarded const qualifiers even though I'm not making any changes to it.

Code:

---

void foo(const map<string, pair<int, int> >& m)
{
  string search_string = "bar";
  int a = m[search_string].first;            // !Error about "passing const map<yadayada> as
                                              //'this' argument of "yada yada" discards qualifiers"
  int b = m[seach_string].second;
}

// the second yada yada in this case is
//'std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key =
//std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::pair<unsigned int,
//unsigned int>, _Compare = std::less<std::basic_string<char, std::char_traits<char>,
//std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char,
//std::char_traits<char>, std::allocator<char> >, std::pair<unsigned int, unsigned int> > >]’

---

Do I have to use the dreaded const_cast?

According to my searches, map:: operator [] is not a const function (in other words, if search_string is not a key value, a new key will be created, hence m will be modified). If you need to work with const, you should use map::find instead.

Of course. Forgot about that. Thanks!