Declaring a string array in GNU C++

Question

To me it seems like it should be so simple, but I just feel like I'm missing something.

I have in my header file a private variable _stoplist When I declared it in the header file the code looks just like this.

private:
    std::string _stoplist[];

But when later in my function I decide to access this, it segfaults on anything.

_stoplist[_length];
//cout << _length << prints 104 (its a valid int and everything)
_stoplist[0] = "b";

Crashes in the std::string.assign() code with a segfault. I have a gut feeling that I'm missing something obvious here but I haven't quite found out what yet.

Thanks in advance!

EDIT: Ok, thanks for all the help. For anyone else who may read this, I would recommend to use one of the answers below since that is the smart way to do it. In my case though since I needed to dynamically allocate it without using vector I just used the following code.

private:
    std::string *_stoplist;

and then in my cpp file

_stoplist = new string[_length];

Yeah, turns out that it really was way simple, and I just was over looking that part.

I just wanted to note that variable length arrays like this aren't legal C++, they're a GCC extension. — bames53
– bames53, Commented Oct 21, 2011 at 3:47

bstamour · Accepted Answer · 2011-10-21 03:39:29Z

2

You're getting an array out of bounds error because _stoplist doesn't have a size. You should either give it a size, and only access elements within that range, such as:

private:
    std::string _stoplist[100];

now you should be able to index _stoplist[0] through _stoplist[99]. However a better solution would probably to use std::vector instead, as it's a lot safer.

private:
    std::vector< std::string > _stoplist;

Then you can use its member functions such as resize() to grow it to whatever size you need.

answered Oct 21, 2011 at 3:39

bstamour

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5 Comments

Bob Over a year ago

As much as I'd like to use std::vector, this is a class assignment so I'm not allowed to. Maybe I should've been clearer in the question, but I do need this list to be dynamically sized, so does that mean that I need to declare it like this: std::string *_stoplist[] and then use _stoplist[] = new string[_length]?

Bob Over a year ago

But this is definitely the right answer for any other person who would have this problem.

GManNickG Over a year ago

@Bob: Tell your teacher he's an idiot, then rewrite a simplified version of vector yourself, if you can.

bstamour Over a year ago

@GMan: That's a great way to start a good relationship with a teacher... I would just code the assignment the way it was asked, and then mention that std::vector is a better choice, not call the teacher names like a child.

GManNickG Over a year ago

@bstamour: I think it was clear I never actually intended for him to do that.

Dolda2000 · Accepted Answer · 2011-10-21 03:40:30Z

1

That's because a variable declared as std::string[] is basically just a pointer. To use it, you need to allocate memory for it. If you want to allocate fixed memory for it, try declaring it as e.g. std::string _stoplist[5]; instead.

answered Oct 21, 2011 at 3:40

Dolda2000

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