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Show Lecture.OtherIterators as a slide show.

CS253 Input/Output Iterators

Not always containers

• As we’ve seen when discussing regular expressions, an iterator doesn’t necessarily have to iterate over a container.
• It is possible to iterator over more abstract things, such as input or output.
• Exotic iterators are declared in <iterator>.

ostream_iterator

The usual way of writing things to cout:

cout << "Always";
cout << " test";
cout << " your code.";

Always test your code.

The ostream_iterator way:

ostream_iterator<string> it(cout);
*it++ = "Always";
*it++ = " test";
*it++ = " your code.";

Always test your code.

ostream_iterator with containers

The usual way of writing things to cout:

vector<string> vs = {"Always", "test", "your code."};
for (auto v : vs)
    cout << v << ' ';

Always test your code. 

The ostream_iterator way:

vector<string> vs = {"Always", "test", "your code."};
ostream_iterator<string> it(cout, " ");
copy(vs.begin(), vs.end(), it);

Always test your code. 

istream_iterator

Consider this file:

$ cat ~cs253/pub/ducks
Huey (red)
Dewey (blue)
Louie (green)

istream_iterator

The usual way to read all strings from the file:

const string home = getpwnam("cs253")->pw_dir;
ifstream in(home + "/pub/ducks");

string s;
while (in >> s)
    cout << "☆☆☆ " << s << '\n';

☆☆☆ Huey
☆☆☆ (red)
☆☆☆ Dewey
☆☆☆ (blue)
☆☆☆ Louie
☆☆☆ (green)

istream_iterator

Using istream_iterator:

const string home = getpwnam("cs253")->pw_dir;
ifstream in(home + "/pub/ducks");

string s;
istream_iterator<string> it(in), eos;
while (it != eos)
    cout << "☆☆☆ " << *it++ << '\n';

☆☆☆ Huey
☆☆☆ (red)
☆☆☆ Dewey
☆☆☆ (blue)
☆☆☆ Louie
☆☆☆ (green)

istream_iterator

Using copy with an istream_iterator and an ostream_iterator:

const string home = getpwnam("cs253")->pw_dir;
ifstream in(home + "/pub/ducks");

istream_iterator<string> it(in), eos;
ostream_iterator<string> out(cout, "\n");

copy(it, eos, out);

Huey
(red)
Dewey
(blue)
Louie
(green)

istream_iterator

Similarly, but displaying ★ after each string:

const string home = getpwnam("cs253")->pw_dir;
ifstream in(home + "/pub/ducks");

istream_iterator<string> it(in), eos;
ostream_iterator<string> out(cout, "★");

copy(it, eos, out);

Huey★(red)★Dewey★(blue)★Louie★(green)★

istream_iterator

Similarly, but working with char, not string:

const string home = getpwnam("cs253")->pw_dir;
ifstream in(home + "/pub/ducks");

istream_iterator<char> it(in), eos;
ostream_iterator<char> out(cout, "★");

copy(it, eos, out);

H★u★e★y★(★r★e★d★)★D★e★w★e★y★(★b★l★u★e★)★L★o★u★i★e★(★g★r★e★e★n★)★

istream_iterator

Similarly, but working with double, not char:

const string home = getpwnam("cs253")->pw_dir;
ifstream in(home + "/pub/ducks");

istream_iterator<double> it(in), eos;
ostream_iterator<double> out(cout, "★");

copy(it, eos, out);

insert_iterator

The insert_iterator inserts into a container by calling .insert():

set<int> source = {678, 901, 234, 567, 890, 123};
list<int> destination = {1, 2, 3, 4, 5};

auto it = destination.begin();
advance(it, 3);                     // Why not it+=3?
insert_iterator<list<int>> insert_it(destination,it);
copy(source.begin(), source.end(), insert_it);
for (auto v : destination)
      cout << v << ' ';

1 2 3 123 234 567 678 890 901 4 5 

Why did the order change?

front_insert_iterator

front_insert_iterator is like insert_iterator, except that it inserts at the front of the container:

unordered_set<int> source = {11111, 22222, 33333, 44444, 55555};
deque<int> destination = {1, 2, 3, 4, 5};

front_insert_iterator<deque<int>> fi(destination);
copy(source.begin(), source.end(), fi);
for (auto v : destination)
      cout << v << ' ';

11111 22222 33333 44444 55555 1 2 3 4 5 

back_insert_iterator

Same thing, other side:

forward_list<char> source = {'b', 'a', 'r'};
string destination = "Foo";

back_insert_iterator<string> bi(destination);
copy(source.begin(), source.end(), bi);
cout << destination << '\n';

Foobar

Convenience functions:

The convenience functions front_inserter() and back_inserter() return front_insert_iterator<T> or back_insert_iterator<T> of the appropriate type:

unordered_set<int> source = {11111, 22222, 33333, 44444, 55555};
deque<int> destination = {1, 2, 3, 4, 5};
auto fi = front_inserter(destination);
copy(source.begin(), source.end(), fi);
for (auto v : destination)
      cout << v << ' ';

11111 22222 33333 44444 55555 1 2 3 4 5 

forward_list<char> source = {'b', 'a', 'r'};
string destination = "Foo";
auto bi = back_inserter(destination);
copy(source.begin(), source.end(), bi);
cout << destination << '\n';

Foobar

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