CODEWITHSUNDEEP
c++iterator
JosephConrad
JosephConrad

Reputation: 688

c++ iterator error

I have a problem with iterator. Could you explain me why this code:

vector<vector<int> >::iterator it = v.begin();
for(; it < v.end(); it++)
{
  vector<int> var = *it;
  sort(var.begin(), var.end() );
}

is ok and with this code:

vector<vector<int> >::iterator it = v.begin();
for(; it < v.end(); it++)
{
  sort(*it.begin(), *it.end() );
}

is wrong? Compiler said that *it has no member begin, but I don;t know why.

Upvotes: 2

Views: 2874

Answers (2)

Zeta
Zeta

Reputation: 105886

The operator "." binds stronger than the operator "*". Try

vector<vector<int> >::iterator it = v.begin();
for(; it < v.end(); it++){
   sort(it->begin(), it->end() );
}

instead.

Your code works like this:

vector<vector<int> >::iterator it = v.begin();
for(; it < v.end(); it++)
{
  sort(*(it.begin()), *(it.end()) );
}

and it simply has no member begin as it is a simple iterator.

Upvotes: 4

James McNellis
James McNellis

Reputation: 355069

Operator precedence.

*it.begin() is the same as *(it.begin()). You need (*it).begin() (or the equivalent expression, it->begin()).

That is, you need to "call the member function begin() of the object pointed to by it," not "deference the result of calling the member function begin() on it" (it has no member function begin(), which is why the compiler gives you the error message that you get).

Upvotes: 11

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