Reading piped input with C++

问题:

I am using the following code:

#include <iostream>
using namespace std;

int main(int argc, char **argv) {
    string lineInput = " ";
    while(lineInput.length()>0) {
        cin >> lineInput;
        cout << lineInput;
    }
    return 0;
}

With the following command: echo "Hello" | test.exe

Thes result is an infinate loop printing "Hello". How can I make it read and print a single "Hello"?

回答1:

string lineInput;
while (cin >> lineInput) {
  cout << lineInput;
}

If you really want full lines, use:

string lineInput;
while (getline(cin,lineInput)) {
  cout << lineInput;
}

回答2:

When cin fails to extract, it doesn't change the target variable. So whatever string your program last read successfully is stuck in lineInput.

You need to check cin.fail(), and Erik has shown the preferred way to do that.