Two problems with std::cin.getline()

**~~master5001~~** · 10-15-2008

Originally Posted by tabstop

Well, but the whole point of ignore is that the only place I know the input isn't going is adminPassword.

Oh ok, gotcha. I see now.

**maxhavoc** · 10-15-2008

Originally Posted by master5001

Thank you

Its nice to have someone second that opinion.

What would that do with the excess input in std::cin? Just silently discard it?

**~~master5001~~** · 10-15-2008

Yep.

**~~master5001~~** · 10-15-2008

You are free to look at this.

**tabstop** · 10-15-2008

Originally Posted by maxhavoc

What would that do with the excess input in std::cin? Just silently discard it?

Well, there wouldn't be any excess input. A string can be whatever number of characters it needs to be; why stop at 16?

And of course, if you need to interface with char *-expecting functions, there is the .c_str() member function of a string.

**~~master5001~~** · 10-15-2008

I don't normally tell people to do this, but the only reason I make an exception today is because this is the 36th post on this thread. And at this point you are just now starting to take the very first suggestion you were given all the way back in post #2 on this thread; feel free to kick yourself.

**whiteflags** · 10-15-2008

Originally Posted by maxhavoc

master5001, the problem with that approach is that allows ONLY 16 characters, not up to and including 16 characters.

This may be another option for you. I'm not gonna bother explaining too much, since this is really simple code.

If you have specific needs then roll your own. The standard IO functions are building blocks, not your personal toolbox of goodies.

Code:

#include <iostream>
#include <ostream>
#include <cstring>

using std::cout;
using std::cin;
using std::endl;

int main ()
{
    const std::streamsize MAX = 17;
    char buffer[MAX];

    const std::streamsize oldw = cin.width();
    cin.width( MAX );
    cout << "Enter 16-character phrase: ";
    cin >> buffer;
    if ( cin.peek() != '\n' || std::strlen( buffer ) < MAX - 1 ) {
        cin.ignore( (unsigned)-1 ); //ignore any extraneous stuff
        cout << "Invalid phrase, try again\n";
    }
    else {
        cin.ignore(); //ignore newline
        cout << "You entered \"" << buffer << "\"" << endl;
    }
    cin.width( oldw );
    //copy buffer, do whatever
}

**maxhavoc** · 10-15-2008

Originally Posted by tabstop

Well, there wouldn't be any excess input. A string can be whatever number of characters it needs to be; why stop at 16?

And of course, if you need to interface with char *-expecting functions, there is the .c_str() member function of a string.

Is there a way to limit the number of characters getline accepts? I know that std::string simply grows as large as it needs, but this could lead to denial of service attack through resource exhaustion if there is no way to limit. Also, is there a way to get the count of elements actually read?

**tabstop** · 10-15-2008

Originally Posted by maxhavoc

Is there a way to limit the number of characters getline accepts? I know that std::string simply grows as large as it needs, but this could lead to denial of service attack through resource exhaustion if there is no way to limit. Also, is there a way to get the count of elements actually read?

gcount still exists.

**maxhavoc** · 10-15-2008

Originally Posted by tabstop

gcount still exists.

String does not have a gcount function. When I try to use std::cin.gcount it returns -1.

**tabstop** · 10-15-2008

Originally Posted by maxhavoc

String does not have a gcount function. When I try to use std::cin.gcount it returns -1.

In that case, use the .size() member function of the string.

**maxhavoc** · 10-15-2008

Originally Posted by tabstop

In that case, use the .size() member function of the string.

Ok, that will work so long as I can restrict the number of characters read in from std::cin during the getline() call. Do you know how I can do that?

**tabstop** · 10-15-2008

Originally Posted by maxhavoc

Ok, that will work so long as I can restrict the number of characters read in from std::cin during the getline() call. Do you know how I can do that?

All I know is that you can't. (TBH, I don't see worrying about a DOS as useful here, since if they can throw 4G characters at your C++ program, they can throw 4G characters at your C program just as well with the same result; you're going to run into the maximum length of stdin well before that anyway, I should think.)

**maxhavoc** · 10-15-2008

Okay, thanks for the help everyone. I think the lesson I'm taking home from this is don't program in C++ anymore if I ever want to have secure console input.