Segmentation fault in std::vector::erase() in Visual C++

Question

I am having a segmentation fault in the erase function of std::vector that is driving me crazy. Am having the following code:

std::map<uint32_t, std::vector<boost::uuids::uuid> >::iterator it
    = theAs.find(lSomeUint32);
if (it != theAs.end()) {
  std::vector<boost::uuids::uuid>& lIds = it->second; // vector contains one entry
  std::vector<boost::uuids::uuid>::iterator it2 = lIds.begin();
  while (it2 != lIds.end()) {
    if (*it2 == lSomeUuid) {
      lIds.erase(it2);
      break;
    }   
    ++it2;
  }   
}

In lIds.erase(it2), I get a segmentation fault. More precisely, I get a segmentation fault in _Orphan_range (can be found in c:\Program Files\Microsoft Visual Studio 10.0\VC\include\vector) that is called from erase. But I have no clue why. The vector and the iterator look ok. But in _Orphan_range, something goes completely wrong. The while loop in there is executed three time although my vector contains one item only. In the third run, the variable _Pnext gets broken.

Does someone have an idea? That would be awesome!

David

Unfortunately (or maybe fortunately), the example above executed standalone works. But inside my big software project, it doesn't work.

Does someone know what the failing function _Orphan_range is executed for?

Carsten Greiner · Accepted Answer · 2011-09-22 18:09:48Z

2

Erasing from std::vector invalidates iterators. see STL vector::erase Therefore it2 is invalid after the first call to erase. Alas the check "(it2 != lIds.end()) " will not be true.

change your code to:

if (*it2 == lSomeUuid) {
  it2 = lIds.erase(it2);
  break;
}

answered Sep 22, 2011 at 18:09

Carsten Greiner

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2 Comments

ssube Over a year ago

As with most other crashes deep within someone else's code (when it's the STL or something similarly widely used and tested), it's probably a tricky problem in yours. and this one, if you aren't paying close attention, can very easily bite you. This is almost certainly your issue.

Andriy Tylychko Over a year ago

how your snippet differs from OP's one?

Andriy Tylychko · Accepted Answer · 2011-09-22 14:22:48Z

0

You compare with wrong end iterator.

std::vector<boost::uuids::uuid>::iterator it2 = lIds.begin();
while (it2 != pIds.end()) {

Note lIds and pIds. Try to use more letters in your variables names and don't use hungarian notation. You'd caught Ids_ptr almost instantly.

answered Sep 22, 2011 at 14:22

Andriy Tylychko

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3 Comments

David Graf Over a year ago

Oh dear. I made a mistake in the example. I changed it.

Andriy Tylychko Over a year ago

Now what you provided looks completely valid

David Graf Over a year ago

Yes, I also looks good to me. I also tested it with valgrind on linux. It's strange.

Ajai · Accepted Answer · 2011-09-22 14:38:46Z

-1

Isn't your

 "theAs.find(lSomeUint32);"

returning the index position rather than the Map::iterator? I'm not sure about this. Can you check it out? The find() function returns the position of the lSomeUint32 in theAs and would return the position of that lSomeUint32 in the string(if it is present). I suppose that is the reason why your erase function is throwing an error. It is not able to erase a data that is not present or that is not in the scope of your program.

Even otherwise if your find() returns the map object I would, in addition to that put a simple if structure to check whether that particular find() returns any object or is NULL just to make sure that the iterator is assigned a value before being operated.

Just a suggestion.

answered Sep 22, 2011 at 14:38

Ajai

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2 Comments

Ajai Over a year ago

Can I know why is this a wrong answer? With the code snippet that was what I was able to infer.

David Graf Over a year ago

Unfortunately (or maybe fortunately), the example above executed standalone works. But inside my big software project, it doesn't work. Does someone know what the failing function _Orphan_range is executed for?

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