Question

On os X 10.8, I tried to redirect std input to c++ string via bash.

After I printed 1024th character, I even cannot press enter.

Could you please explain where the problem occurs and how to fix it?

Answer 1

The problem has nothing to do with bash, or with the C++ code. To verify this, this trivial program has the same problem:

#include <iostream>
#include <string>
int main(int, char**) {
    std::string s;
    std::getline(std::cin, s);
}

And so does this Python program:

#!/usr/bin/python
raw_input()

And you can try running under different shells and see that it makes no difference.

The problem is that a TTY in line mode always has a max line length, and this one happens to have a max line length of 1024.

So, this isn’t even really a programming question; it’s a TTY question. Which is why you can find a dup over at superuser.com instead of here. See the discussions there on the various ways to deal with this.

However, if you want to deal with it from within your program, rather than globally, you can check whether stdin is a tty, and if so use termios functions to temporarily turn off line mode. For example, something like this:

#include <iostream>
#include <string>
#include <termios.h>
#include <unistd.h>

int main(int, char**) {
  struct termios told;

  if (isatty(STDIN_FILENO)) {
    tcgetattr(STDIN_FILENO, &told);
    struct termios tnew = told;
    tnew.c_lflag &= ~ICANON;
    tcsetattr(STDIN_FILENO, TCSAFLUSH, &tnew);
  }

  std::string s;
  std::getline(std::cin, s);

  if (isatty(STDIN_FILENO)) {
    tcsetattr(STDIN_FILENO, TCSAFLUSH, &told);
  }
}

However, you’ll obviously want real error handling, and you’ll probably want to use RIAA to stash and restore the original termios settings, and you should probably read man termios to understand what you’re doing and what other effects it will have (and whether you want to do anything else).