Question

I am utterly mystified by this error, and I hope you can help me!
I have a class which has a vector of structures (the structure is called particle). I am simply writing a getter which returns a vector of a certain field in the structure; once for a field called x, and then again for a field called v:

vector<double> x = s.getx();
vector<double> v = s.getv();

For some reason, getx works, but getv does not: It gives me “malloc(): memory corruption:”.

Here are the classes getx and getv:

vector<double> getx() {

    vector<double> ret(number-2);

    for(int i = 1; i < number; i++) {

        ret[i-1] = masses[i].x;

    }

    return ret;

}

vector<double> getv() {

    vector<double> ret(number-2);

    for(int i = 1; i < number; i++) {

        ret[i-1] = masses[i].v;

    }

    return ret;

}

The error occurs on this line:

vector<double> ret(number-2);

in getv.

The reason I am so confused is that both these methods are essentially identical! I even get the same error when I replace (number-2) with a constant, e.g. 4. It simply can’t allocate the memory!

I hope you can see what I’ve done wrong…

Thank you very much for your help,
Best wishes,
noctilux

Answer 1

Memory corruption errors rarely show up at the point where they occur; they show up later, when something hits the corrupted memory. In this case, both functions are writing to memory that doesn’t belong to them. Each one initializes a vector with number - 2 elements, then writes to vector[number - 1], which doesn’t exist.