Bad access on reading vector iterator

Question

I have a vector<int> called pitches. I'm getting periodic bad access on the last line below:

int play = 0;
bool didFind = 0;
vector<int>::const_iterator iterator;

for (iterator = pitches.begin(); iterator != pitches.end(); ++iterator) {
    if (*iterator > lastpitch) { // lastpitch is an int
        didFind = 1;
        play = *iterator;
        break;
    }
}

if (!didFind) play = *(pitches.begin()); // this line gives me bad access

I had previously tried *pitches.begin() on the last line but that always provided bad access and I understand that now. But while I get it less often now, this play=*(pitches.begin()); is still doing the same occasionally. I cannot see anything in the above that would cause that, any suggestions appreciated.

Is the vector empty at that point, perhaps? (In particular, taking into account that `didFind` is false there.) — jogojapan, Feb 18 '13 at 02:40
A note on style: it's generally preferable to use true/false instead of 1/0 when dealing with `bool`s. — jaymmer - Reinstate Monica, Feb 18 '13 at 02:43
Related: http://stackoverflow.com/questions/9598621/c-why-does-dereferencing-this-vector-iterator-segfault — jogojapan, Feb 18 '13 at 02:52

score 4 · Accepted Answer · answered Feb 18 '13 at 02:41

4

If pitches vector has size 0, the things inside

      for (iterator=pitches.begin();iterator!=pitches.end();++iterator)

doesn't get executed and therefore didFind=0.

The statement inside if is evaluated. Yet pitches is empty means pitches.begin()==pitches.end(). Dereferencing a pitches.end() is to access out of bound and therefore gives bad access.

answered Feb 18 '13 at 02:41

phoeagon

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I'll debug but I'm quite certain the vector is never empty. I'll find out shortly, thanks. – johnbakers Feb 18 '13 at 02:42
@SebbyJohanns then add a `assert(pitches.size())` before all these sequence to check. – phoeagon Feb 18 '13 at 02:43
Indeed there was an isolated case when the vector could be empty. – johnbakers Feb 18 '13 at 02:48

Bad access on reading vector iterator

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