try/catch missing vector subscript out of range (debug assertion failed) - c++

Question

I have some code, where I'm using std::forward_list
Part of my code tests for vector subscripts being out of range, as well as if the element in the vector has certain properties (in this case, is not -1).
When I have just the first or second node of the list, it works fine and I can catch the error, as that's just a normal part of the program. However, on the next loop around, when I have 3 elements in the list, I get the vector subscript out of range debug assertion, and it isn't caught by my try/catch. Is there a different technique I must use to resolve this error?
Here's a snippet of the code, where it's problematic:
for(int i = 0; i < 8; i++)
{
if(curr->moves[i].at(0) >= 0 && curr->moves[i].at(1) >= 0)
{
next->setPos(curr->moves[i].at(0),curr->moves[i].at(1)); //just sets values of a vector
next->setMoves(); //sets values of a 2d vector
for(int j = 0; j < 8; j++)
{
try{if(board.kBoard[next->moves[i].at(0)][next->moves[i].at(1)] != -1) //the debug assertion is thrown here, but I cannot catch it
next->moves[i].at(2) = 1;}
catch(out_of_range const &err)
{next->moves[i].at(2) = 1;}
}
...
}
}
I've commented where the issue occurs. You'll (at least on my screen) have to scroll to the right to see it. I believe that, potentially, I can use another catch statement, but I don't know which error to use, given that I'm already using out_of_range, which normally would handle this issue. A screenshot of what the error looks like when it's thrown is this. To be completely clear, the issue occurs at try{if(board.kBoard[next->moves[i].at(0)][next->moves[i].at(1) != -1), where I have commented. It doesn't go to the catch statement at all, I think because it's using _DEBUG_ERROR()

Answer 1

While, theoretically, a try/catch statement could catch the error here, it isn't wise to intentionally cause errors as part of an algorithm; try/catch should be used to report when errors happen. In this case, I should have used:
if(next->moves[i].at(0) >= 0 && next->moves[i].at(1) >= 0) //1
if(board.kBoard[next->moves[i].at(0)][next->moves[i].at(1)] != -1) //2
next->moves[i].at(2) = 1; //3
else
next->moves[i].at(2) = 1; //3
This allows me to check if the subscript is out of range (1), check if an element of the board is not -1 (2), and set moves[i].at(2) to 1, in those cases (3).
This avoids any out_of_range errors, obviating the need for try/catch entirely.