istream_iterator invokes reading from the keyboard by just defining it!!

[JUANDENT]

Hi,

The following code opens for reading from the keyboard instead of waiting for the vector: (this does not occur if the istream is an ifstream - associated with a file)

istream_iterator<string> in {cin }; // this reads the keyboard immediately why??
istream_iterator<string> eos;
vector<string> vec{ in, eos };     // this is where I expect reading the keyboard!! 

[JLBorges]

The actual read operation is performed when the iterator is incremented, not when it is dereferenced.
The first object is read when the iterator is constructed.
Dereferencing only returns a copy of the most recently read object.
https://en.cppreference.com/w/cpp/iterator/istream_iterator

[JUANDENT]

This activates reading but I can never close the input unless I write Ctrl-Z or Ctrl-C... why doesn't it end reading when I press ENTER?

vector<string> vec{ istream_iterator<string> {cin }, istream_iterator<string> {}};
bool eof = cin.eof();  // this return true 

must do cin.clear() in order to continue reading from cin... Why necessary?

[JUANDENT]

this line of reading does not end when pressed ENTER, why?

vector<string> vec{ istream_iterator<string> {cin }, istream_iterator<string> {}}

[Peter87]

Pressing enter does not end the stream.

[JUANDENT]

Then how come ENTER terminates input for this instruction?

istream_iterator<string> in {cin };

Try it out please

[Peter87]

Because of what JLBorges posted.

The first object is read when the iterator is constructed.

Once it has read that one first string token the code continues.

[seeplus]

Pressing enter does not end the stream.

Correct. This iterates the stream until eof is found (istream_iterator<string> {}). For Windows cin, eof is ctrl-z. So to terminate the input enter ctrl-z on a line by itself.

#include <iostream>
#include <vector>
#include <string>

using namespace std;

int main() {
	vector<string> vec{ istream_iterator<string> {cin }, istream_iterator<string> {}};

	for (const auto& v : vec)
		cout << v << '\n';
}

This will generate vec from the input with a new element inserted for every white space in the input. The input is terminated with ctrl-z

foobar barfoo
^Z
foobar
barfoo

foorbar barfoo is entered. Then ctrl-Z to terminate. Then the contents of vec are displayed.