Question

I’m having a problem resizing my two dimensional vectors.

std::vector<std::vector<NavigationNode>> *nodes;
nodes->resize(sizex);

for(unsigned int i=0; i<sizex ;i++)
    nodes[i].resize(sizey);

It works as intended when i is 0, but crashes when i is 1.

Do you know why?

Answer 1

You’ve defined the type of nodes to be a pointer to a vector of vectors. Presuming that this pointer has been initialized to correctly allocated memory, nodes[i] is not calling operator[] on the outer vector, it’s accessing the memory nodes points to as if it is a contiguous array. It is equivalent to *(nodes+i).

In this case, more correct syntax would be (*nodes)[i].

std::vector<std::vector<NavigationNode>> *nodes;
nodes->resize(sizex);

for(unsigned int i=0; i<sizex ;i++)
    (*nodes)[i].resize(sizey); //line changed