How to compare two QString arrays Qt C++

Question

i want to compare two QString Array with Qt and C++, i tried this, but it dosent work, (in fact my application crash...) :

if(ArrayOne[nb] != ArrayTwo[nb]){

}

And then i need to assign a value at an element of my array, but i dosent work too :

ArrayOne[nb] = ArrayTwo[nb];

To reach this :

if(ArrayOne[nb] != ArrayTwo[nb]){
ArrayOne[nb] = ArrayTwo[nb];
}

THANKS !

nb is an int, arrayone and two are declared like that : QString ArrayOne; — Random78952, Nov 13 '12 at 21:03
Also, what exactly does "doesn't work" imply? Does it not compile? Does it compile but behave differently than you expected? Differently how? — Armen Tsirunyan, Nov 13 '12 at 21:03
Yes it compile, i have edited my post : "(in fact my application crash...)" — Random78952, Nov 13 '12 at 21:04
OK, what value is in the strings? What value does nb have? If nb is larger than the string size (or equal to it) you will get undefined behavior (which includes crash) — Armen Tsirunyan, Nov 13 '12 at 21:04
Also, QString ArrayOne; is not an array of Qstrings, it's simply a QString — Armen Tsirunyan, Nov 13 '12 at 21:05
the int nb is generated like that : qrand() % ((high + 1) - low) + low; low and hight are between 1 and 10 — Random78952, Nov 13 '12 at 21:06
Have you tried [strcmp](http://www.cplusplus.com/reference/clibrary/cstring/strcmp/)? — Emmanuel N, Nov 13 '12 at 21:06
Judging from your http://stackoverflow.com/questions/13367458/display-array-content-in-a-list-widget-qt-c question, it seems you don't understand the basic workings of arrays in C++. I'd suggest you pick some beginner's tutorial for C. — Nikos C., Nov 13 '12 at 21:35

score 1 · Accepted Answer · answered Nov 13 '12 at 21:15

1

Your nb value is probably outside the range for the size of your QString. i.e., nb > ArrayOne.size-1.

answered Nov 13 '12 at 21:15

Phlucious

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The nb value is between 1 and 10 – Random78952 Nov 13 '12 at 21:17
1

But what is the content of ArrayOne? – Phlucious Nov 13 '12 at 21:19

score 1 · Answer 2 · answered Nov 13 '12 at 21:24

You say you have:

QString ArrayOne;

If this is true, then you are just comparing characters in two strings, not string arrays, at position nb. And QString's operator[] does not check range, so if nb is more than length of QString, program may very well crash, especially if you assign to invalid reference returned by QString::operator[]...

So, to be clear: your code probably crashes because nb >= ArrayOne.length()

How to compare two QString arrays Qt C++

2 Answers2