xon1c xon1c - 13 days ago 8
C++ Question

Vector.erase(Iterator) causes bad memory access

I am trying to do a Z-Index reordering of

videoObjects
stored in a
vector
. The plan is to identify the
videoObject
which is going to be put on the first position of the
vector
, erase it and then insert it at the first position. Unfortunately the
erase()
function always causes bad memory access.

Here is my code:

testApp.h:

vector<videoObject> videoObjects;
vector<videoObject>::iterator itVid;


testApp.cpp:

// Get the videoObject which relates to the user event
for(itVid = videoObjects.begin(); itVid != videoObjects.end(); ++itVid) {
if(videoObjects.at(itVid - videoObjects.begin()).isInside(ofPoint(tcur.getX(), tcur.getY()))) {
videoObjects.erase(itVid);
}
}


This should be so simple but I just don't see where I'm taking the wrong turn.

Answer

You should do

itVid = videoObjects.erase(itVid);

Quote from cplusplus.com:

[vector::erase] invalidates all iterator and references to elements after position or first.

Return value: A random access iterator pointing to the new location of the element that followed the last element erased by the function call, which is the vector end if the operation erased the last element in the sequence.

Update: the way you access the current element inside your condition looks rather strange. Also one must avoid incrementing the iterator after erase, as this would skip an element and may cause out-of-bounds errors. Try this:

for(itVid = videoObjects.begin(); itVid != videoObjects.end(); ){
  if(itVid->isInside(ofPoint(tcur.getX(), tcur.getY()))){
    itVid = videoObjects.erase(itVid);
  } else {
    ++itVid;
  }
}