are there any risk to get garbage value when casting unsigned long to int?

Question

I want to assign the ARRAY_SIZE(X) to an int. are there any risk to get garbage value in the int since ARRAY_SIZE(X) is an unsigned long

#define ARRAY_SIZE(X) (sizeof((X))/sizeof((X)[0]))
int m = ARRAY_SIZE(X)

are there a risk to get garbage value in m?

Only if the value is greater than `INT_MAX`. Integer casts are well-defined. — Ry-, Feb 20 '17 at 13:53
`ARRAY_SIZE(X)` is `size_t`, which you really should be using as the type of `m`. — StoryTeller - Unslander Monica, Feb 20 '17 at 13:53
Why are you asking if there is *any* risk when you already have an example where garbage is produced? — Scott Hunter, Feb 20 '17 at 14:07
@ScottHunter, In fact I want to be sure that the cause is casting issue. and to understand why — MOHAMED, Feb 20 '17 at 14:11
To be pedantic you could check `if ( ARRAY_SIZE(X) > INT_MAX ) { ...error handling...}` before proceeding — M.M, Feb 21 '17 at 07:30

Petr Skocik · Accepted Answer · 2017-02-21T07:16:33.693

You shouldn't get garbage (as in completely unpredictable) values.

Narrowing conversions to signed types when the value won't fit in the target type will either be implementation-defined or they'll raise a signal (6.3.1.3p3).

If they don't raise a signal, you can verify absence of information loss by checking the values and signs of the source and destination are the same.

(If you store into unsigneds, the conversion will always be well defined, and you'll only need to compare the values (no signs in unsigned types) to verify absence of information loss.)

score -1 · Answer 2 · answered Feb 20 '17 at 13:54

-1

If the value in ARRAY_SIZE(x) is bigger than what can fit in an int, you can't help but get garbage.

answered Feb 20 '17 at 13:54

Scott Hunter

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I get garbage value when array size is 0 – MOHAMED Feb 20 '17 at 13:57
If an element is part of an array, and the array size is 0, what would you expect the element size to be? – Scott Hunter Feb 20 '17 at 14:06
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@MOHAMED - An array size of 0 is not allowed. Your compiler should complain – StoryTeller - Unslander Monica Feb 20 '17 at 14:17

are there any risk to get garbage value when casting unsigned long to int?

2 Answers2