max_element function

[daviddoria]

I'm just trying to figure out how this stuff works. I wrote this function:

#include <algorithm>
#include <vector>
	double VectorMax(const vector<double> &a)
	{
		vector<double>::iterator pos;
		pos = max_element (a.begin(), a.end());
		return *pos;
	}

and call it with:

vector<double> Numbers;
	Numbers.push_back(3.4);
	Numbers.push_back(4.5);
	Numbers.push_back(1.2);
	
	cout << VectorMax(Numbers) << endl;

but I get "no match for operator=" error. Since this is just a container of doubles, shouldn't = already be defined?

Thanks,
Dave

[nucleon]

You should use a const_iterator: vector<double>::const_iterator pos; I'm assuming you have a using namespace std; in your actual code. (Please post runnable code.)

[daviddoria]

Yep, that did it, thanks. Forgot about the const iterators.
Sorry I forgot to include "using namepace std;"

Dave

[daviddoria]

I tried to make a template out of this:

template <typename T>
	T VectorMax(const vector<T> &a)
	{
		vector<T>::const_iterator pos;
		pos = max_element (a.begin(), a.end());
		return *pos;
	}

but now I get "error: expected ; before 'pos' "

[nucleon]

Declare your iterator like this: typename vector<T>::const_iterator pos;

[daviddoria]

That worked. Why do you have to do that?

[nucleon]

I'm not exactly sure! I've learned to try typename in situations like that.

Obviously it's disambiguating something. It isn't needed if you use a concrete type like int instead of T, so it has something to do with that. Apparently the compiler cannot be sure exactly what a vector<T>::const_iterator is and needs the hint that it is indeed a typename.

Perhaps a C++ guru can tell us more.