Calculating size of an array

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That’s because the size of an int * is the size of an int pointer (4 or 8 bytes on modern platforms that I use but it depends entirely on the platform). The sizeof is calculated at compile time, not run time, so even sizeof (arr[]) won’t help because you may call the foo() function at runtime with many different-sized arrays.

The size of an int array is the size of an int array.

This is one of the tricky bits in C/C++ – the use of arrays and pointers are not always identical. Arrays will, under a great many circumstances, decay to a pointer to the first element of that array.

There are at least two solutions, compatible with both C and C++:

  • pass the length in with the array (not that useful if the intent of the function is to actually work out the array size).
  • pass a sentinel value marking the end of the data, e.g., {1,2,3,4,-1}.

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