arraysize

Arraysize is a term used to describe the number of elements that an array can hold. The concept appears in many programming languages, but the exact mechanism to obtain it varies: it can be a macro, a function, or a language intrinsic. In practice, arraysize helps write code that iterates over an array, allocates appropriate storage, or performs bounds checking, while highlighting the distinction between fixed-size arrays and dynamically sized collections.

In C and C++, a common technique to obtain the number of elements in a statically declared array is a macro or template that computes sizeof(array)/sizeof(array[0]). This yields a compile-time constant when used with a real array. The approach does not work for pointers or dynamically allocated arrays, where the size must be tracked separately. Because of this limitation, arraysize is often used only with actual arrays, not with function parameters that decay to pointers.

Many modern languages provide built-in ways to determine size without relying on an arraysize macro. For example, Python uses len(array), JavaScript uses array.length, and many languages offer a size or length method for fixed-size containers. In C++, the standard library provides std::size (since C++17) and containers like std::vector expose a size() method, offering safer and more flexible means to obtain the element count.

Common pitfalls include misapplying arraysize to pointers, which removes the size information, and assuming fixed-size arrays remain unchanged. When working with dynamic data, it is safer to track length separately or rely on language-provided size facilities.

See also: array length, fixed-size array, dynamic array, size, length, std::size.