C++ Notes: Example - readArray

Here is a function to read from cin into an array, written in three different styles.

1. Using reference parameter and array

This simple solution uses the array size to avoid a buffer overflow, but silently ignoring the error of too much input is not good. Throwing an exception would be a more robust solution.

void readArray(int a[], int& n, int maxsize) {
    // function:
    //    Reads from cin until array full or to an EOF.
    // parameters:
    //    a       out  array destination of values.
    //    n       out  number of values in a, a[0]..a[n-1]
    //    maxsize in   maximum number of elements that can fit in a
    // returns: 
    //   nothing
   
    n = 0;  // start with an empty array.
    while (n < maxsize  &&  cin >> a[n]) {
        n++;
    }
    return;
}

2. Using pointer for array and reference parameter for size

Rewriting the above using the equivalent int* instead of the array type.

void readArray(int* a, int& n, int maxsize) {
    n = 0;  // start with an empty array.
    int* limit = a + maxsize;  // address after last element
    while (a < limit  &&  cin >> *a) {
        a++;
        n++;
    }
    return;
}

As before, a call would look like

   readArray(temps, size, 1000);

3. Using all pointers

Changing the reference parameter to a pointer looks like this:

void readArray(int* a, int* n, int maxsize) {
    *n = 0;  // start with an empty array.
    int* limit = a + maxsize;  // address after last element
    while (a < limit  &&  cin >> *a) {
        a++;
        *n = *n + 1;
    }
    return;
}

Because the size parameter is a pointer, the call must be written as

readArray(temps, &size, 1000);