C++/STL Algorithms Iterator/iterator
Advance the iterator
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <list>
#include <algorithm>
using namespace std;
int main()
{
list<int> coll;
// insert elements from 1 to 9
for (int i=1; i<=9; ++i) {
coll.push_back(i);
}
list<int>::iterator pos = coll.begin();
// print actual element
cout << *pos << endl;
// step three elements forward
advance (pos, 3);
// print actual element
cout << *pos << endl;
// step one element backward
advance (pos, -1);
// print actual element
cout << *pos << endl;
}
/*
1
4
3
*/
Convert iterator to reverse iterator
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
vector<int> coll;
// insert elements from 1 to 9
for (int i=1; i<=9; ++i) {
coll.push_back(i);
}
// find position of element with value 5
vector<int>::iterator pos;
pos = find (coll.begin(), coll.end(),
5);
// print value to which iterator pos refers
cout << "pos: " << *pos << endl;
// convert iterator to reverse iterator rpos
vector<int>::reverse_iterator rpos(pos);
// print value to which reverse iterator rpos refers
cout << "rpos: " << *rpos << endl;
}
/*
pos: 5
rpos: 4
*/
Find a value in map by key
#include <iostream>
#include <map>
using namespace std;
int main()
{
map<char, int> m;
// put pairs into map
for(int i=0; i<26; i++) {
m.insert(pair<char, int>("A"+i, 65+i));
}
char ch = "G";
map<char, int>::iterator p;
// find value given key
p = m.find(ch);
if(p != m.end())
cout << "Its ASCII value is " << p->second;
else
cout << "Key not in map.\n";
return 0;
}
/*
Its ASCII value is 71
*/