Invincible Macros for C++(2) : For Iterator

When I started learning C++, I kind of thought that the "iterator" was really irritating.

What do you think?

I now think that iterators are similar to pointers and that I understand their convenience.

But it takes rather long time for you to write sources with iterators.

See the code below:

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// e.g. 1

#include <iostream>

#include <vector>

#include <list>

using namespace std;

int main() {

　　　vector<int> vec;

　　　vec.push_back(1);

　　　vec.push_back(12);

　　　vec.push_back(167);

　　　vector<int>::iterator vec_p;

　　　for (vec_p = vec.begin(); vec_p < vec.end(); vec_p++)

　　　　　　cout << *vec_p << endl;

　　　return 0;

}

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In fact, you don't have to use iterators when you want to do stuff I listed above.

You can access to an element of the vector vec by using a pair of blankets and the corresponding index, like vec[i].

But you can't access to list's element this way.

So when you use list, you've got to utilize iterators like below:

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// e.g. 2

#include <iostream>

#include <vector>

#include <list>

using namespace std;

int main() {

　　　list<int> lt;

　　　lt.push_back(1);

　　　lt.push_back(3);

　　　lt.push_back(5);

　　　list<int>::iterator lt_p;

　　　for (lt_p = lt.begin(); lt_p != lt.end(); lt_p++)

　　　　　　cout << *lt_p << endl;

　　　return 0;

}

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Please notice that the exit criteria is different from that of vector.

Iterator for list don't have the operator "<" or ">", so you have to use "!=".

Ummm, the iterator part is loooog, don't you think?

Then how's this?

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// e.g. 3

#include <iostream>

#include <vector>

#include <list>

#define fori(it, x) for (__typeof((x).begin()) it = (x).begin(); it != (x).end(); it++)

using namespace std;

int main() {

　　　// for vector

　　　vector<int> vec;

　　　vec.push_back(1);

　　　vec.push_back(12);

　　　vec.push_back(167);

　　　fori(vec_p, vec)

　　　　　　cout << *vec_p << endl;

　　　// for list

　　　list<int> lt;

　　　lt.push_back(1);

　　　lt.push_back(3);

　　　lt.push_back(5);

　　　fori(lt_p, lt)

　　　　　　cout << *lt_p << endl;

　　　return 0;

}

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