为什么 std::istream_iterator 忽略换行符？

Question

I have the following code:

#include <sstream>
#include <iterator>
#include <iostream>

int main()
{
    std::stringstream str; str << "abc\ndef";

    std::cout << "[" << str.str() << "]" << std::endl;

    std::istream_iterator<char> it(str), end;

    for (; it != end; ++it)
    {
        std::cout << "[" << unsigned(*it) << "]";
    }

    std::cout << std::endl;

    return 0;
}

And the output is:

[abc
def]
[97][98][99][100][101][102]

Why std::istream_iterator ignored the new-line character?

Answer 1

Because istream_iterator uses operator>> . And istream::operator>>(char) skips whitespace, unless you unset the skipws flag of the stream. (eg using noskipws )

It's the same output you would get if you did this:

char c;
while (str >> c)
    std::cout << "[" << unsigned(c) << "]";

Answer 2

You can disable skipping any whitespace in the input by changing a little bit of your code:

std::stringstream str; str << std::noskipws << "abc\ndef";

New output:

[abc
def]
[97][98][99][10][100][101][102]

Answer 3

改用std::istreambuf_iterator<char> ，它不会丢失空格和换行符。