通过判断该向量的元素来擦除2d向量c ++的一个向量

Question

vector< vector<int> > 2d_vector;

here 2d_vector is an*3 vector where n indicates the element of it, eg 2d_vector = { {0,0,2}, {0,0,1}, {0,0,0}, {0,0,-1} }

I was trying to erase elements of this 2d_vector that fit "2d_vector[i][2] == -1", where i is from 0 to n. My code is as follows:

vector< vector<int> >::iterator it = 2d_vector.begin();
    for( ;it<2d_vector.end();it+=3){
        if(**(it+2) == -1){         
            it = staticBlocks.erase(it); 
        }
    }

But it does not work. How should I do? Thank you in advance.

Answer 1

Let's break down **(it+2) . it+2 refers to the second vector after the one referenced by it . *(it+2) dereferences the iterator and gets the second vector after the one referenced by it . This is a vector , not a pointer or an iterator. It cannot be dereferenced, so **(it+2) is doomed. However, (*(it+2))[0] Should do what you appear to want.

This assumes it+2 is within range.

Answer 2

You meant that kind of thing? :

std::vector<std::vector<int>> vec;
    for (std::vector<std::vector<int>>::iterator it = vec.begin(); it != vec.end(); ++it) {
    if (it->at(2) == -1){
        vec.erase(it);
        --it; // This may fix it, if a vector gets deleted, the rest of the list goes one step towards the beggining of it and the next vector will be skipped
    }
}

It fits to this

erase elements of this 2d_vector that fit "2d_vector[i][2] == -1",