Re: [Libusb-devel] msvc warning in libusb.h about zero-sized array

[Peter S. <pe...@st...>]

Francesco wrote:
> I'm not sure to understand why libusb uses:
> #if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)
> 	[] /* valid C99 code */
> #else
> 	[0] /* non-standard, but usually working code */
> #endif
> 	;
> instead of a simple pointer declaration...

As was mentioned, array entry 0 is stored where this struct member
starts, followed by entry 1, and so on. It's not a pointer, it's an
array - but with unknown length. All places where the struct size
needs to be known must somehow find out how many array entries are
included in it - sizeof() and other compiler helpers do not work.


> anyway I fear that the fact MSVC is unable to generate the
> copy-ctor or the copy-assignment operators may create some
> very-hard-to-detect bugs (since you can still write "t1 = t2;"
> where t1,t2 are libusb_transfer structs!)...

That will not work. You must manually handle all of the array
entries; first alloc enough memory for t1 so that there is room, then
possibly you can use t1=t2; but you must manually copy the array
entries anyway, so you might as well just copy the entire struct
instead and have less code.


> PS: btw setting /W4 makes the compiler spit out lots of other warnings
> and some of them could be pointing to real problems; e.g.
> 
>  warning C4305: 'type cast' : truncation from 'list_head *' to 'unsigned long'
>  warning C4306: 'type cast' : conversion from 'int' to 'HANDLE' of greater size
>  warning C4706: assignment within conditional expression

Interesting! Can you show the places in the code that triggers these?


//Peter