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STL-error?

Jedyte · 2003-06-04T12:33:20

Hi, Anyone has a clue how this code can give an Access Violation error (you know: 0xC0000005)? Here's a simplified version: typedef std::list<int> PositionList; PositionList _trail; // some actions on list... if(_trail.size() >= 2) { // for every two points that follow PositionList::const_iterator t1 = ++_trail.begin(); // invalid access crash here PositionList::const_iterator t2 = _trail.begin(); PositionList::const_iterator one_before_end = --_trail.end(); for(; t1 != one_before_end; ++t1, ++t2) { // a line is drawn between points // nothing dangerous } }It crashes when trying to increment the iterator. The only reason I can think of a crash there is when the list doesn't have the required number of elements. But even after adding an extra check like this does the crash happen (also in the increment): if(_trail.size() >= 2) { // for every two points that follow to one before last PositionList::iterator t1 = _trail.begin(); if(t1 != _trail.end()) ++t1; else log << "Ack!"; PositionList::const_iterator t2 = _trail.begin(); PositionList::const_iterator one_before_end = --_trail.end(); // rest... Anybody help? [edited by - Jedyte on June 3, 2003 5:14:47 PM]

General and Gameplay Programming Programming

Started by Jedyte June 03, 2003 04:12 PM

12 comments, last by Jedyte 20 years, 10 months ago

Qw3r7yU10p!

819

June 04, 2003 06:38 AM

if this is a member function of a class then make sure the class'' object is valid.

Jedyte

122

Author

June 04, 2003 12:01 PM

Hmm, I think something's wrong in the destructor of the class.
Could it be that because I don't have an (empty) virtual destructor in a derived class, that it gives the error? In what cases is a virtual destructor needed when using polymorphism?

[edited by - Jedyte on June 4, 2003 1:03:15 PM]

And the price we paid was the price men have always paid for achieving paradise in this life -- we went soft, we lost our edge. - "Muad'Dib: Conversations" by the Princess Irulan

Kylotan

10,510

June 04, 2003 12:08 PM

Jedyte

122

Author

June 04, 2003 12:18 PM

Got it! Thanks Kylotan, your idea brought me back on track.
It was a stupid list::back() when the list was empty. Cheez, I've been programming in STL for over 4 years, you'd think I'd wouldn't make such a mistake anymore %)

To return to my other question now that we're on it, if I write this, will the destructors be called correctly?

class Base{  Base();  virtual ~Base(); // virtual here};class Derived: public Base{  Derived();  // but nothing here, we don't need it};

Thanks.

[edited by - Jedyte on June 4, 2003 1:33:20 PM]

And the price we paid was the price men have always paid for achieving paradise in this life -- we went soft, we lost our edge. - "Muad'Dib: Conversations" by the Princess Irulan

STL-error?

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STL-error?

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