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Interesting C++ bug involving `std::cin` for input.

 2 years ago
source link: https://dev.to/baenencalin/interesting-c-bug-involving-stdcin-for-input-14gg
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Calin Baenen

Posted on Nov 27

Interesting C++ bug involving `std::cin` for input.

So, I was making hangman for fun, and I had

unsigned short guesses;
std::string    word;

std::cin << guesses;
// ...
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And I discovered something interesting.
I was just playing around, and I typed 1, and spammed a bunch of 0s.
Sort of like the following.

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And then it did something really strange, it skipped the next std::cin command (which was the one for word).
And then... it kept repeating, printing things over and over (probably because I was in a while(true)), but it didn't bother to stop when it hit std::cin, even on the next loop iteration, instead constantly having the number be equal to 65535, (2^16)-1; or in other words, the 16 bit integer (unsigned short) limit.

Even if I enter 65536, the unsigned short limit plus one, it still bugs out in this crazy way.

Here's an image of what happens after I do this:

Literally only a second after I submit my answer of raw `65536` endraw .

This is what should happen normally:

Strangely, this bug will also happen if I pass any strings that include a space () character in them for answer (for some reason).

This is my code:

int main() {
  while(true) {
    unsigned short guesses;
    std::string    answer;

    std::cout << "Enter the amount of guesses to allow: ";
    std::cin >> guesses;
    std::cout << "Enter the word for P2 to guess: ";
    std::cin >> answer;

    std::cout << "[Guesses: " << guesses << ", " << "Word: \""
      << answer << "\"]\n";
  }
}
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If anyone knows what's causing these bugs, and how I can fix them, let me know!

Thanks!
Cheers!


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