Passing an array by reference to a function - c++

Question

I need help passing an array to a function by reference. The array is created beforehand being passed to the function but the value of the array after being passed through the function is not what I want - it remains unchanged. The code is shown below. The function is to take an array, a position p and a value val. The array is assumed to be sorted in ascending order up to position p and the value val must be placed such that the array is sorted in ascending order up to position p+1.
#include <iostream>
using namespace std;
// Function that takes an array a, a position,
// and a float value val to insert.
// a must already be sorted in acsending order
// up to p. val is then inserted such that
// the a is sorted up to p+1.
// p = 0 means position a[0].
void insert(double (&a)[], int aSize, int p, double val)
{
try {
// Throw error if p > size of array
if(p > aSize || p < 0) {
throw logic_error("Position is greater than size of array or less than zero.");
}
int newSize = aSize + 1;
double* vTemp = new double[newSize]; // create new bigger array
for(int i = 0; i <= p; i++) {
if(val >= a[i]) {
vTemp[i] = a[i];
} else {
vTemp[i] = val;
for(int j = i + 1; j < newSize; j++) {
vTemp[j] = a[j - 1];
}
break;
}
}
cout << "Size of vTemp = " << newSize << endl;
for (int k = 0; k < newSize; k++){
cout << "vTemp[" << k << "] = " << vTemp[k] << endl;
}
a = vTemp;
delete[] vTemp;
} catch(const logic_error& e) {
cout << "Error in input: " << e.what() << endl;
}
}
int main()
{
// Declare variables
double myArray[] = { 1, 2, 4, 8, 16, 20, 50, 30, 153 }; // sample array to test function
int p = 5; // position
double val = 7.2; // value to insert
int arraySize = sizeof(myArray) / sizeof(myArray[0]); // no. of elements in array
int newSize = 0; // size of expanded matrix
// Insert val
insert(myArray, arraySize, p, val);
cout << "Size of original array: " << arraySize << endl;
// Display new expanded matrix
newSize = sizeof(myArray) / sizeof(myArray[0]); // size of expanded matrix
cout << "Size of expanded array: " << newSize << endl << endl;
for(int i = 0; i < newSize; i++) {
cout << myArray[i] << " ";
}
cout << endl;
// Return success
return 0;
}

Answer 1

Don't use raw arrays. The class you are looking for is called std::vector (reference).
Just create a vector instead of an array and pass it by reference and you get what you need.

Answer 2

The problem doessn't come from the array being passed by reference.
The issues is assigning a dynamic array to a built-in array.
In the case above, when the following statement is executed.
a = vTemp;
The "array , which by that point is a pointer reference" will change is value to point to the dynamic array.
But don't forget that you are deleting the array.
delete[] vTemp;
you are not actually copying each element that the dynamic allocated array have into your array. when execution goes back to main, it points to your normal array.