How can I fix an assertion failure that states 'vector subscript out of range' [closed] - c++

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Debug Assertion Failed: Vector subscript out of range
Debug Assertion Failed Vector Subscript Out of Range C++
I am working on a Boids project, details of which can be found here:
https://www.red3d.com/cwr/boids/
From what I can gather my issue is something to do with an index getting accessed by the function but no data is present in the index. I had this issue yesterday in a different area of my code and fixed it by making one of my getters return a reference rather than a copy of a class object. That approach seems to not be the issue today.
Below is my code:
This code is a snippet from my function that handles simulation events. This is the code that I have narrowed down the issue to.
//Remove flocking organisms with < 0 enery storage.
for (int i = 0; i < m_flock.getSize(); i++)
{
if (m_flock.getOrganism(i).getEnergyStore() <= 0)
{
m_flock.removeOrganism(i);
//m_notFlocking.flock.erase(m_notFlocking.flock.begin() + i);
cout << "Organism died and has been removed..." << endl;
}
}
The code below is from my Flock.cpp class definition file which details information on storing boids in a vector to then apply flocking behaviors to. This class function is giving the following error:
Unhandled exception at 0x7B87FC66 (ucrtbased.dll) in EvoSim.exe: An invalid parameter was passed to a function that considers invalid parameters fatal.
Code:
Organism &Flock::getOrganism(int i)
{
return flock[i];
}
My suspicion is that the for loop size is not reflecting the recently erased object.
How can I fix the vector subscript error?
Edit:
This is the break point that shows up in the debugger:
_NODISCARD _Ty& operator[](const size_type _Pos) noexcept /* strengthened */ {
auto& _My_data = _Mypair._Myval2;
#if _CONTAINER_DEBUG_LEVEL > 0
_STL_VERIFY(
_Pos < static_cast<size_type>(_My_data._Mylast - _My_data._Myfirst), "vector subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0
return _My_data._Myfirst[_Pos];
}
Edit 2:
I did some messing around and discovered the issue only occurs when I run VS 2019 in debug mode, otherwise in Release mode it works fine and as expected.

Answer 1

I see nothing in this code that can cause an out of bounds access. However, you should not increment i on any loop iteration that removes an organism, otherwise you will skip the next organism in the list.
Imagine on the 1st loop iteration, the organism at index 0 needs to be removed. Subsequent organisms move down the list. On the next loop iteration, i gets incremented to 1, and the organism that had moved into index 0 is skipped.
Try this instead:
//Remove flocking organisms with < 0 enery storage.
for (int i = 0; i < m_flock.getSize(); )
{
if (m_flock.getOrganism(i).getEnergyStore() <= 0)
{
m_flock.removeOrganism(i);
cout << "Organism died and has been removed..." << endl;
}
else
++i;
}
Alternatively, you can replace the entire loop using the erase-remove idiom via std::remove_if() and std::vector::erase(), eg:
void Flock::removeDeadOrganisms()
{
//Remove flocking organisms with < 0 enery storage.
flock.erase(
std::remove_if(flock.begin(), flock.end(),
[](const auto &o){ return o.getEnergyStore() <= 0; }
),
flock.end()
);
}
...
m_flock.removeDeadOrganisms();
Or, in C++20, via std::erase_if(), eg:
void Flock::removeDeadOrganisms()
{
//Remove flocking organisms with < 0 enery storage.
std::erase_if(flock,
[](const auto &o){ return o.getEnergyStore() <= 0; }
);
}

Answer 2

To loop though a vector that you are also modifying you don't want to i++ on every loop, since if the element was removed you don't need to increment the index. There are two solutions to this, either you can conditionally increment the index at the end of the loop or you can loop though the list backwards.
int i = 0;
while (i < m_flock.getSize())
{
if (m_flock.getOrganism(i).getEnergyStore() <= 0)
{
m_flock.removeOrganism(i);
cout << "Organism died and has been removed..." << endl;
}
else
{
i++;
}
}
for (int i = m_flock.getSize(); i ; i--)
{
if (m_flock.getOrganism(i).getEnergyStore() <= 0)
{
m_flock.removeOrganism(i);
cout << "Organism died and has been removed..." << endl;
}
}
You can't use a normal iterator loop for this because vector::erase "Invalidates iterators and references at or after the point of the erase, including the end() iterator". However, you can use std::remove_if.
m_flock.erase(std::remove_if(m_flock.begin(),
m_flock.end(),
[](Organism org){
return org.getEnergyStore()<=0;
}));