Re: Array Size

James Kanze <>
Mon, 1 Jul 2013 05:24:18 -0700 (PDT)
On Saturday, 29 June 2013 15:12:30 UTC+1, David Brown wrote:

On 28/06/13 22:40, =D6=F6 Tiib wrote:


I need array that may have up to 20000 elements. To indicate the state
of the array I use variable that is valid in range from 0 to 20000.
How is using 'int16_t' or 'uint16_t' (or whatever you suggest) making i=


*clear* that the code is correct?

If your array has 40000, then using int32_t or uint16_t makes
it clear that the index type will work properly - using "int"
does not.

Not at all. If your array has 40000, then it will only work if
the index has values in the range 0..39999. This is not
a constraint of any built-in type, on any machine that I know

Regardless of the type, you have to range check. This is
normally done by validating the input, well upstream of where
you're actually indexing.

How is using 'int', 'ssize_t' or 'size_t' (or whatever you suggest)
making it *unclear*? 'int' is most logical and most simple choice.

These sorts of types are okay on their own, but as soon as you
have to store them, convert them, manipulate them, or do
arithmetic on them, it is easier to see correctness if you
know exactly what type sizes you have.

That is simply false. Well written software doesn't depend on
any specific sizes. It validates all input against the values
it can handle.

To ensure maximum correctness I write simple static_assert
that the required limits fit into numeric_limits<int> and
a pile of unit tests. The fixed width types are no way
magic bullet and help from them is minimal.

So you have a static assertion somewhere to ensure that (for
example) "int" is 32-bit, and then later in the code you use
"int" knowing it is 32-bit? What possible benefit is that
over writing "int32_t" when you want a 32-bit integer?

The static assertion is more likely along the lines of
MAX_INT > 40000. With the advent of std::vector, and
dynamically sized arrays, of course, you're more likely to use
a dynamic check:

    if ( input > MAX_INT / sizeof( MyType ) ) {
        throw IllegalInputError();

"int32_t" says exactly what you want

Except that int32_t does NOT say exactly what I want. On one
hand, it says too much (2s complement, exactly 32 bits). On the
other, it doesn't say enough (value in the range 0 to 40000).
It's misleading. It's obfuscation.


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