Re: [ros-dev] [ros-diffs] [pschweitzer] 50612: [NTOSKRNL/PPC] Fix the fix, spotted by "ThFabba" on IRC

[Timo Kreuzer]

Under "normal conditions" sizeof of an array covers the whole array. is 
this different for function paramters?

Am 06.02.2011 14:50, schrieb [e-mail]:
> Author: pschweitzer
> Date: Sun Feb  6 13:50:57 2011
> New Revision: 50612
>
> URL: http://svn.reactos.org/svn/reactos?rev=50612&view=rev
> Log:
> [NTOSKRNL/PPC]
> Fix the fix, spotted by "ThFabba" on IRC
>
> Modified:
>      trunk/reactos/ntoskrnl/ke/powerpc/cpu.c
>
> Modified: trunk/reactos/ntoskrnl/ke/powerpc/cpu.c
> URL: http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/powerpc/cpu.c?r...
> ==============================================================================
> --- trunk/reactos/ntoskrnl/ke/powerpc/cpu.c [iso-8859-1] (original)
> +++ trunk/reactos/ntoskrnl/ke/powerpc/cpu.c [iso-8859-1] Sun Feb  6 13:50:57 2011
> @@ -44,7 +44,7 @@
>   CPUID(IN ULONG CpuInfo[4],
>         IN ULONG InfoType)
>   {
> RtlZeroMemory(CpuInfo, sizeof(CpuInfo) * sizeof(ULONG));
>
> RtlZeroMemory(CpuInfo, 4 * sizeof(ULONG));
> }
>
> VOID

[Roel Messiant]

Hey,

Yes, array arguments are just simple pointers in C, so sizeof will
return the size of a pointer to the base type.
Exercise for the reader: Predict what happens when you try passing an
int[4] into an int[8] argument.

WBR,

Roel Messiant

2011/2/6 Timo Kreuzer [e-mail]:
> Under "normal conditions" sizeof of an array covers the whole array. is this
> different for function paramters?
>
> Am 06.02.2011 14:50, schrieb [e-mail]:
> > Author: pschweitzer
> > Date: Sun Feb  6 13:50:57 2011
> > New Revision: 50612
> >
> > URL: http://svn.reactos.org/svn/reactos?rev=50612&view=rev
> > Log:
> > [NTOSKRNL/PPC]
> > Fix the fix, spotted by "ThFabba" on IRC
> >
> > Modified:
> >     trunk/reactos/ntoskrnl/ke/powerpc/cpu.c
> >
> > Modified: trunk/reactos/ntoskrnl/ke/powerpc/cpu.c
> > URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/powerpc/cpu.c?r...
> >
> > ==============================================================================
> > --- trunk/reactos/ntoskrnl/ke/powerpc/cpu.c [iso-8859-1] (original)
> > +++ trunk/reactos/ntoskrnl/ke/powerpc/cpu.c [iso-8859-1] Sun Feb  6
> > 13:50:57 2011
> > @@ -44,7 +44,7 @@
> >  CPUID(IN ULONG CpuInfo[4],
> >        IN ULONG InfoType)
> >  {
> > RtlZeroMemory(CpuInfo, sizeof(CpuInfo) * sizeof(ULONG));
> > RtlZeroMemory(CpuInfo, 4 * sizeof(ULONG));
> >
> > }
> >
> > VOID
>
> Ros-dev mailing list
> [e-mail]
> http://www.reactos.org/mailman/listinfo/ros-dev

[Pierre Schweitzer]

Hi,
this is a bit tricky, but it is the way it works.
In case you still have doubts, enjoy that C program. You will never reach the memset:

#include <assert.h>
#include <string.h>

void test_sizeof(unsigned long test[4], char c) {
    assert(sizeof(test) == (4 * sizeof(unsigned long)));
    memset(test, c, sizeof(test));
}
void main() {
    unsigned long tab[4];
    test_sizeof(tab, '?');
}

Regards,
P. Schweitzer
> Hey,
>
> Yes, array arguments are just simple pointers in C, so sizeof will
> return the size of a pointer to the base type.
> Exercise for the reader: Predict what happens when you try passing an
> int[4] into an int[8] argument.
>
> WBR,
>
> Roel Messiant