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 pschweitzer(a)svn.reactos.org:
>   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?…
>  ==============================================================================
>  --- 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 <timo.kreuzer(a)web.de>de>:
>  
>  Under "normal conditions" sizeof of an array covers the whole array. is this
>  different for function paramters?
>
>
>
>  Am 06.02.2011 14:50, schrieb pschweitzer(a)svn.reactos.org:
> >  
> >  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?…
> >
> >  ==============================================================================
> >  --- 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
> >
> >
> >  
>
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>

[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
>