Question

I’m working on an assignment right now where we create our own basic, dynamically allocated vector struct. One of the functions we are supposed to make is a function to extend the vector when the user enters values.

struct Vector{//vector structure
    unsigned int size;
    Elem *svector;
};

Vector *extend_vec(Vector *extend,Elem element){
    if (extend==NULL){
        return NULL;}


    Elem *tempVec=new Elem[(*extend).size];

    memcpy(tempVec,(*extend).svector,sizeof((*extend).svector));//copies memory from the original array to the temp array

    (*extend).size+=1;

    delete[] (*extend).svector;//clears the memory

    (*extend).svector=new Elem[(*extend).size];//reallocates with the new size


}

Elem=float btw**

My question is whether this line is necessary, and why :

 delete[] (*extend).svector;//clears the memory

I’m a bit hazy on how memory is overwritten/reallocated in a situation like this. I’m not sure if reallocating overwrites whats already there.

**So I read through everyone’s comments and this is what I came up with.

Vector *extend_vec(Vector *extend,Elem element){
    if (extend==NULL){
            return NULL;}


    Elem *tempVec=new Elem[extend->size+1];
    tempVec[extend->size+1]=element;

     memcpy(tempVec,extend->svector,(extend->size*sizeof(Elem)));//copies the memory from the original array to the rest of the temp array

    extend->size+=1;

    delete[] extend->svector;//clears the memory

    extend->svector=tempVec;//the original vector now becomes the extended vector

    delete[] tempVec;//clears the temporary memory

    return extend;
}

Answer 1

I don’t think the code presented here will work as expected. I think what you want is:

Elem *tempVec = new Elem[extend->size +1];
tempVec[extend->size] = element;
memcpy(tempVec, extend->svector, extend->size);
delete[] extend->svector;
extend->svector = tempVec;
extend->size += 1;