void trim(std::string& str);

void foo()
{
  std::vector<std::string> v;
  //...
  for (std::vector<std::string>::iterator it = v.begin(); it != v.end(); ++it)
  {
    trim(*it);
  }
}

  std::string trim2(const std::string& str);
  
  void bar()
  {
    std::vector<std::string> v;
    //...
    std::transform(v.begin(), v.end(), v.begin(), trim2);
  }

  std::set<std::string> s;
  s.insert("A")
  s.insert("B");

  *s.begin() = "C";
  //... oops

Q>  std::set<std::string> s;
Q>  s.insert("A")
Q>  s.insert("B");

Q>  *s.begin() = "C";
Q>  //... oops
Q>

error: passing 'const std::basic_string<char>' as 'this' argument of 'std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>, std::basic_string<_CharT, _Traits, _Alloc> = std::basic_string<char>]' discards qualifiers [-fpermissive]

Q>void trim(std::string& str);

Q>void foo()
Q>{
Q>  std::vector<std::string> v;
Q>  //...
Q>  for (std::vector<std::string>::iterator it = v.begin(); it != v.end(); ++it)
Q>  {
Q>    trim(*it);
Q>  }
Q>}
Q>

The algorithm for_each is very flexible, allowing the modification of each element within a range in different, user-specified ways.

template<class InIt, class Fun>
    Fun for_each(InIt first, InIt last, Fun f);

The template function evaluates f(*(first + N)) once for each N in the range [0, last - first).
It then returns f. The call f(*(first + N)) must not alter *(first + N).

Z>если у тебя это не так, значит твой STL или компилятор