A working std::copy example - printing an array

Question

This does not work. I'm trying to learn how to use std::copy but I can't find any working code. I ran this in gcc 4.6.1. And it does not do anything when I hit control D. If I hit Control C...it prints out the new lines only.

Found code here:

Printing an array in C++?

#include <iostream> 
#include <vector> 
#include <algorithm> 
#include <iterator> 

int main() 
{ 
    std::vector<int>    userInput; 

    // Read until end of input. 
    // Hit control D   
    std::copy(std::istream_iterator<int>(std::cin), 
              std::istream_iterator<int>(), 
              std::back_inserter(userInput) 
             ); 

    // Print in Normal order 
    std::copy(userInput.begin(), 
              userInput.end(), 
              std::ostream_iterator<int>(std::cout,",") 
             ); 
    std::cout << "\n"; 

    // Print in reverse order: 
    std::copy(userInput.rbegin(), 
              userInput.rend(), 
              std::ostream_iterator<int>(std::cout,",") 
             ); 
    std::cout << "\n"; 
} 

Answer 1

Not sure how you're running it or what you're entering but that seems to run fine for me:

pax$ g++ -o qq qq.cpp ; ./qq
1
2
3
4
5
0
9
8
7
6
<CTRL-D>
1,2,3,4,5,0,9,8,7,6,
6,7,8,9,0,5,4,3,2,1,

This is with gcc 4.3.4 under Cygwin. One thing to watch out for is that (in my environment at least), CTRL-D has to be entered on a new line. Entering:

1 2 3 4 5<CTRL-D>

didn't work for me (the CTRL-D was ignored) but:

1 2 3 4 5
<CTRL-D>

did.

You can bypass those issues with CTRL-D by doing something like:

echo 1 2 3 4 5 6 7 8 9 0 | ./qq

so that end of file does not depend on your terminal characteristics. This is especially important since it may be that MinGW (being a Windows application rather than running under CygWin's emulation layer) requires the Windows end-of-file character, CTRL-Z.

Running this command acts as expected:

pax$ echo 1 2 3 4 5 6 7 8 9 0 | ./qq
1,2,3,4,5,6,7,8,9,0,
0,9,8,7,6,5,4,3,2,1,