“std::bad_alloc”: am I using too much memory?

Question

The message:

terminate called after throwing an instance of 'std::bad_alloc'
what():  std::bad_alloc

I looked at the gdb backtrace and this is the lowest level method in there that I implemented myself:

/*
 * get an array of vec3s, which will be used for rendering the image
 */
vec3 *MarchingCubes::getVertexNormalArray(){
    // Used the same array size technique as getVertexArray: we want indices to match     up
    vec3 *array = new vec3[this->meshPoints.getNumFaces() * 3]; //3 vertices per face

    int j=0;
    for (unsigned int i=0; i < (this->meshPoints.getNumFaces() * 3); i++) {
        realVec normal = this->meshPoints.getNormalForVertex(i);
 //     PCReal* iter = normal.begin();

        if (normal.size() >= 3) {
            array[j++] = vec3(normal[0], normal[1], normal[2]);
        }
        cout << i << " ";
    }

    return array;
}

The cout statement you see above indicates that it terminates after 7000+ iterations. The above function is called only once near the end of my application. I call a very similar function before calling the above, that doesn't cause problems.

Answer 1

My problem turned out to be that this->meshPoints.getNormalForVertex(i) accesses an array (or vector, I can't remember) whose length is less than this->meshPoints.getNumFaces() * 3. So it was accessing out of bounds.

Answer 2

(moving/expanding from the comments)

Since you are allocating a new array every time without deallocating it, you have a massive memory leak, i.e. you continue to ask memory to the system without ever giving it back. Eventually the space on the heap finishes, and at the next allocation all you get is a std::bad_alloc exception.

The "C-style" solution would be to remember to deallocate such memory when you don't need it anymore (with delete[]), but, this is (1) error-prone (think e.g. if you have multiple return paths inside a function) and (2) potentially exception-unsafe (every instruction becomes a potential return path if you have exceptions!). Thus, this way should be avoided.

The idiomatic C++ solution is to use either smart pointers - small objects that encapsulate the pointer and deallocate the associated memory when they are destroyed - or standard containers, that do more or less the same thing but with copy semantics and some more bells and whistles (including storing the size of the array inside them).

Answer 3

I got this error trying to allocate a negative length array:

double myArray = new double[-9000];

Just in case it helps anyone.