getline not working properly

[jessemelhuish]

So, I'm trying to do something simple: get a line into a string, and I have this:
getline (ins, temp);
But, it never seems to stop, in that I hit enter as many times as I want and get nothing. Why? Thanks in advance!

[buffbill]

Try substituting cin for ins

[jessemelhuish]

ins is an input stream, so that wouldn't really be helpful. I did try that though, and it did the same thing as before. This is embedded in a function inside of a class, I can post the entire function if it would be helpful, not that it gets to the rest of the function.

[hanst99]

Did you actually enter a character? IIRC getline will ignore newlines that come before any other characters were read.

[jessemelhuish]

Yes, I enter three letters, each followed by a space. This is part of the extraction operator (>>) for a class that describes a resistor. The idea is to read in the line, determine how many spaces are present, if none, then the user entered just the numeric value, so I would then convert it to an integer, if two then I use a switch statement to assign the colors of the resistor. Here is the code:

istream & operator >> (istream & ins, const Resistor & resi)
{
    string temp;
    int numspaces(0), pos(0);

    getline (ins, temp);

    cout << "here";

    while (pos < temp.length())
    {
        if (temp.find(' ') >= 0)
        {
            numspaces++;
            pos = temp.find(' ') + 1;
        }
        else
        {
            pos = temp.length();
        }
    }

    cout << numspaces;
    return ins;
}

I stopped at this point to see if my logic for determining number of spaces was correct, but I'm never seeing here printed to the screen. I'm sure its something simple.

[hanst99]

Just to make sure... you are calling it like this:
cin>>resi;
and enter something like

a b c ENTER

? In that case, I have really no idea what could be causing this. What compiler are you using, and what command line client? May be a bug.

PS: Shouldn't the Resistor argument be nonconst when you're writing an extraction operator?

[jessemelhuish]

Yes to the first two. I'm using an IDE called Code::Blocks, which using GCC. I have considered it, but I have a hard time believing in anything being noticeably wrong with GCC, though I'll look into it. Ahhh, yes, you are right, not that I think that is affecting it...I probably would have run into that later lol. Thanks for pointing it out, probably would have been a headache later!

[hanst99]

Do you use the GCC version that's being shipped with Code::Blocks? I am not sure, but it might be an outdated one. Oh, and what OS are you using? Windows? Then are you using MinGW or Cygwin GCC?

[jessemelhuish]

Code::Blocks says GCC 4.3.2 32-bit, and I'm using Code::Blocks 10.05. I'm running an Ubuntu based Linux distro called UberStudent. I can post the entire class if it would be helpful.

[jessemelhuish]

Oh, I just discovered that if I type only one letter followed by a space and then hit enter, it works. It must be one letter only, followed by a space.

[ne555]

When outputting debugging and errors messages use cerr instead of cout. (the output is flushed)

    while (pos < temp.length())
    {
        if (temp.find(' ') >= 0) //you always start looking from the beginning 
        {
            numspaces++;
            pos = temp.find(' ') + 1;
        }

[jessemelhuish]

I'll keep that in mind. Thanks for the loop, though that is not the problem seeing as it never gets there. Fixed code:

istream & operator >> (istream & ins, Resistor & resi)
{
    string temp;
    int numspaces(0), pos(0);

    getline(ins, temp);

    cout << "here";

    while (pos < temp.length())
    {
        if (temp.find(' ', pos) >= 0)
        {
            numspaces++;
            pos = temp.find(' ', pos) + 1;
        }
        else
        {
            pos = temp.length();
        }
    }

    cout << numspaces;
    return ins;
}

[jessemelhuish]

I wanted to clarify, by fixed I was only referring to the pointed out issues, it still doesn't work lol

[jessemelhuish]

Well, that's interesting. I was just adding comments, so I recompiled, and what do you know it works...sort of. If you type "a b c" it doesn't work, but if you type "a b c " it does, it relies on that last space.. Strange that I tried that before and it didn't work!

[ne555]

You didn't fixed the cout. Check out your processor usage, it enter in an infinite loop.

http://www.cplusplus.com/reference/string/string/find/

If the content is not found, the member value npos is returned.

//if (temp.find(' ', pos) >= 0)
if( temp.find(' ', pos) != std::string::npos )

[jessemelhuish]

I'll go ahead and change it since I think that is the more accepted way, but it doesn't infinite loop, and it did return the right value. I'll leave this open for a day to see if anybody can figure out why the space is necessary for it to work and then I'll mark as solved.

[jessemelhuish]

getline is again giving me trouble, this time it throw a segmentation fault. Here is the new code:

istream & operator >> (istream & ins, Resistor & resi)
{
    string temp;    //For the line
    int numspaces(0), pos(0);

    getline(ins, temp); //Get the line
    cout << temp;

    while (pos < temp.length()) //While we still have a string to search
    {
        if (temp.find(' ', pos) != std::string::npos)   //Find a space starting at pos
        {
            cout << "here";
            numspaces++;    //Increase number of spaces
            pos = temp.find(' ', pos) + 1;  //Update position
        }
        else    //No space was found
        {
            pos = temp.length();    //End the loop
        }
    }

    cout << numspaces;

    switch (numspaces)
    {
        case 0:
            resi.set_resistance(atoi(temp.c_str()));
            break;
        case 2:
            pos = 0;
            string temp2;

            for (int count = 0;count < 3;count++)
            {
                temp2 = temp.substr(pos, temp.find(' ', pos) - pos - 1);

                pos = temp.find(' ', pos);

                resi.colors[count] = static_cast<ColorCode>(resi.int_equ(temp2));
            }

            resi.convert_to_int();
            break;
    }

    return ins;
}

If I type "47000", it works. If I type "yellow violet orange" is says segmentation fault. It worked once too...so strange.

[ne555]

Assuming that the colours array has the right dimension

  //if you already passed by an space
temp2 = temp.substr(pos, temp.find(' ', pos) - pos - 1); //second argument is -1 (subtract all you can)
  pos = temp.find(' ', pos); //pos is not changing 

So temp2 = " violet orange", maybe that is causing issues in Resistor::int_equ or later on Resistor::convert_to_int

[jessemelhuish]

Good point, but the problem is that it never gets there, I put a cout right after the getline, and the line entered is never outputted, it just returns Segmentation Fault.

[ne555]

*sigh*
That's because cout is buffered. Flush the output with cout << flush; or cout << endl; or change cout to cerr (that is not buffered)