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cin and how much I hate it... =+)

Arcand (11)
im trying to write a basic program based of a game loop, it calls function setup, says something, waits for info, then loops basically the same thing for functions input/compute/update. doing this because im a newb, actually. uber-noob. booya :)

so the problem ive run in to is clearing the cin buffer completely. for instance:

cin.getline(temp, 100) will absolutley spaz if I put it 101 characters, more specificaly for every character I go over, one section of my loop is run in advance. HELP!

im guessing if I find a way to clear the cin.get/cin.getline "buffer" it will work?
LB (13399)
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cin.clear(); //clears errors in case of invalid input
cin.sync(); //ignores everything that has not been read in yet
Arcand (11)
can you put those in a code snippet for me im having trouble using them :S
LB (13399)
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do
{
    int x = 0;
    cout << "Please input the password: ";
    cin >> x;
    if(!cin)
    {
        cin.clear();
        cin.ignore();
        cout << "The password must be numbers only." << endl;
        continue;
    }
    if(x != 1337)
    {
        cout << "Incorrect." << endl << endl;
    }
}while(x != 1337);
cout << "Correct! You are now elite." << endl;
cin.sync();
cout << "Press enter to continue...";
cin.ignore();
 
Please input the password: C++
The password must be numbers only.
Please input the password: 123
Incorrect.

Please input the password: 1337
Correct! You are now elite.
Press enter to continue...
Last edited on
Arcand (11)
Thx meng!
Duthomhas (13206)
That code can bomb for a number of reasons.

All user input should be carefully validated. As a beginner, it is easiest if you just get all user input with std::getline() and use, if necessary, an istringstream to get some thing(s) out of it.

If you want to skip that, then you must be sure to properly synchronize the user's input to what you expect next.

The iostream sync() method isn't actually required to do anything, which makes it useless (and it actually is useless on many systems). Alas.


But that is a digression. For your (Arcand's) stated problem, I have to wonder why you are not using the std::string class with std::getline() to get user input? This will simplify your life considerably.

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#include <algorithm>
#include <cctype>
#include <iostream>
#include <string>
using namespace std;

int main()
  {
  string users_input;

  cout << "> ";
  while (getline( cin, users_input ))
    {
    // Convert the user's input to lowercase
    transform(
      users_input.begin(),
      users_input.end(),
      users_input.begin(),
      (int(*)(int)) std::tolower
      );
    // Act based upon the user's input
    if (users_input == "quit") break;
    else if (users_input == "hello") cout << "Greetings Earthling!\n";
    else if (users_input == "bye") cout << "Oh, no! Don't tell me to quit!\n";
    else cout << "What?\n";
    cout << "> ";
    }

  cout << "Well, goodbye then.\n";
  return 0;
  }
 
> hello
Greetings Earthling
> what's up
What?
> HELLO
Greetings Earthling
> bye
Oh, no! Don't tell me to quit!
> good bye!
What?
> quit
Well, goodbye then.

Foo. Silly example, but hopefully helpful.
biplav17 (159)
why dont you use scanf if you hate ciin so much ?
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