Question

I want to create a vector of data, but I want to both set it’s size and fill its elements in a sub-function. Is this an appropriate time to use the new operator? Is there a better way to do it? It seems like an appropriate time, but I’m hesitant because of Why should C++ programmers minimize use of 'new'?

int main()
{
    vector<double> *array1;
    vector<double> *array2;
    OtherArgs otherArgs;
    FillArrays(array1,array2,otherArgs);
    //Do other stuff 
    delete array1;
    delete array2;
}

void FillArrays(vector<double> *&array1, vector<double> *&array2, OtherArgs &otherArgs)
{
    int size=GetSize(otherArgs);
    array1 = new vector<double>(size);
    array2 = new vector<double>(size);
    //Other code to fill the arrays
}

Thank you

Answer 1

Here are a couple of reasons why the original sample is troublesome

• The code leaks memory in the face of an exception because the delete calls aren’t protected
• If FillArrays is passed a non-NULL vectory<double> value it will leak memory because it didn’t delete the previous value. It couldn’t reliably call delete even if it wanted to because the value may have been stack allocated.

The easiest way to do this is to just declare the values on the stack and pass them by reference that way.

int main()
{
    vector<double> array1;
    vector<double> array2;
    OtherArgs otherArgs;
    FillArrays(array1,array2,otherArgs);
    //Do other stuff 
}

void FillArrays(vector<double> &array1, vector<double> &array2, OtherArgs &otherArgs)
{
    int size=GetSize(otherArgs);
    //Other code to fill the arrays
}

The vector<T> will initialize themselves to an empty list when declared in this manner. The FillArrays method can then populate them as necessary.