🚀 go-pugleaf

vosse@ruls41.fsw.LeidenUniv.nl (Theo Vosse) writes:

>[...] If I have a function
>
>void Add(DataPoint* dp, char v[N])
>{
>    ... sizeof(v) ...
>}
>
>Should sizeof(v) be
>
>a) 4
>b) N
>c) Another value?

`sizeof(v)' should be equal to `sizeof(char *)' (i.e. 4 on typical 32-bit
implementations).

The reason is that the type of `v' is converted from `char [N]' to
`char *' (see 8.3.5/3 in the April draft working paper).
You cannot pass arrays by value in C or C++ (at least not
unless you wrap them up in a struct or class).

>However, both ARM and some ANSI proposal on the net (the September working
>paper?) state:
>
>* When applied to an array, the result is the total number of bytes in the
>array.

That is not relevant in this example, since despite the declaration,
`v' is not an array.

>The ANSI paper also explicitly adds:
>
>* [...] array-to-pointer [...] standard conversions are suppressed on the
>operand of sizeof.

Again, this does not apply - `v' is not an array, so of course the
array-to-pointer standard conversion cannot be applied.  The change
of the type of `v' from array to pointer (since the declaration of
`v' is in a function parameter) is not an instance of the
array-to-pointer standard conversion described in 4.2 which applies to
values.  It is a special "adjustment" that is specified in 8.3.5/3,
not a conversion in the usual C++ sense of the word.

--
Fergus Henderson             	WWW: http://www.cs.mu.oz.au/~fjh
fjh@cs.mu.oz.au              	PGP: finger fjh@128.250.37.3
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