Passing Arrays To/From Functions

Array Parameters

Note

Only discussing one dimensional array in this document. Read the passing 2d array document as needed.

  • pass an array is the same as passing a pointer

  • only the first part (pointer part) is passed, data part stays

  • use [] syntax or * syntax

     1// ==== Array parameter ====
 2// ---- Correct ----
 3
 4// ignore the size
 5double average(double arr[], int size);
 6double average(double *arr, int size);
 7
 8// ---- Wrong ----
 9double average(double arr[size], int size);  // not compile
10double average(double arr[3], int size);  // compile but 3 is ignored
11
12// ---- to call ----
13double arr1[3] = {1.0, 2.0, 3.0};
14cout << average(arr1, 3) << endl;
15// cout << average(arr1[], 3) << endl;  // wrong!

Return an Array

  • Returning an array is the same as returning a pointer

  • Only the first part (pointer part) is passed to outside, data part stays

  • The return type should use pointer syntax

  • Never return a local array from a function

     1// ==== Array as returned value ====
 2
 3// ---- Correct ----
 4// return a dynamic array
 5int *makeSequence(int size) {
 6  int *sequence;
 7  sequence = new int[size];
 8  for (int i = 0; i < size; ++i)
 9    sequence[i] = i + 1;
10  return sequence;
11}
12
13// ---- Wrong ----
14int *makeSequence(int size) {
15  int sequence[size];
16  for (int i = 0; i < size; ++i)
17    sequence[i] = i + 1;
18  return sequence;
19}
20
21// ---- to call ----
22int *seq = makeSequence(10);
23delete [] seq;

  • Read the returning multidimensional arrays document as needed