Unsafe code: Converting "byte *" to "[] byte"

[_BNC]

I've converted "[] byte" to "byte *" at times, using 'unsafe' and
fixed { .... }, but the reverse does not seem to work.

In this case, a C++ DLL returns a byte * and a length. What is the best
way to convert these to straight C#-compatible straight "[] byte" arrays?

PS: The C++ DLL is actually managed and I have access to the source.
Perhaps there is a simpler syntax for doing the conversion there, and
returning a C# compatible array rather than a pointer?

[Bob Powell [MVP]]

Re: Unsafe code: Converting "byte *" to "[] byte"

You'll need to create a byte array and copy the contents of the pointer to
it.

The Marshal class will enable you to do this.

byte[] bytes=new byte[length];
for(int i=0; i<length; i++)
bytes[i]=Marshal.ReadBy te(fromPointer, i);

bytes now contains the copy of the memory pointed to by fromPointer.

Marshal.Copy goes the other way, from the byte array to the pointer. Shame
they couldn't have written a copyfrom method.

--
Bob Powell [MVP]
Visual C#, System.Drawing

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"_BNC" <_BNC@nospam.or g> wrote in message
news:ms7gr0dn7q 7gua23f4h3mbpqk kpopl7j3s@4ax.c om...[color=blue]
> I've converted "[] byte" to "byte *" at times, using 'unsafe' and
> fixed { .... }, but the reverse does not seem to work.
>
> In this case, a C++ DLL returns a byte * and a length. What is the best
> way to convert these to straight C#-compatible straight "[] byte" arrays?
>
> PS: The C++ DLL is actually managed and I have access to the source.
> Perhaps there is a simpler syntax for doing the conversion there, and
> returning a C# compatible array rather than a pointer?
>[/color]

[Willy Denoyette [MVP]]

Re: Unsafe code: Converting &quot;byte *&quot; to &quot;[] byte&quot;


"Bob Powell [MVP]" <bob@_spamkille r_bobpowell.net > wrote in message
news:%23rPUwnd3 EHA.3624@TK2MSF TNGP14.phx.gbl. ..[color=blue]
> You'll need to create a byte array and copy the contents of the pointer to
> it.
>
> The Marshal class will enable you to do this.
>
> byte[] bytes=new byte[length];
> for(int i=0; i<length; i++)
> bytes[i]=Marshal.ReadBy te(fromPointer, i);
>
> bytes now contains the copy of the memory pointed to by fromPointer.
>
> Marshal.Copy goes the other way, from the byte array to the pointer. Shame
> they couldn't have written a copyfrom method.
>[/color]

This has been taken care of in v2.0 using an overload of Marshal.Copy.

Willy.

[_BNC]

Re: Unsafe code: Converting &quot;byte *&quot; to &quot;[] byte&quot;

[re turning 'byte *' into C# '[] byte'

On Thu, 9 Dec 2004 13:48:14 +0100, "Willy Denoyette [MVP]"
<willy.denoyett e@pandora.be> wrote:
[color=blue]
>
>"Bob Powell [MVP]" <bob@_spamkille r_bobpowell.net > wrote in message
>news:%23rPUwnd 3EHA.3624@TK2MS FTNGP14.phx.gbl ...[color=green]
>> You'll need to create a byte array and copy the contents of the pointer to
>> it.
>>
>> The Marshal class will enable you to do this.
>>
>> byte[] bytes=new byte[length];
>> for(int i=0; i<length; i++)
>> bytes[i]=Marshal.ReadBy te(fromPointer, i);
>>
>> bytes now contains the copy of the memory pointed to by fromPointer.
>>
>> Marshal.Copy goes the other way, from the byte array to the pointer. Shame
>> they couldn't have written a copyfrom method.
>>[/color]
>
>This has been taken care of in v2.0 using an overload of Marshal.Copy.
>
>Willy.[/color]

The horror. Runtime is bad enough already. Is there no way to do this
without copying bytes? I'm going through both an unmanaged C++ layer and
then a managed C++ layer before it gets to C#. Is there a simple way to
cast this somewhere in the C++ layers?

I'm also not sure why I'd have to use 'Marshall' to copy the array. If
I've already got a pointer and length, I could just do the copy directly,
right? OK, I'm probably being dense.

[Willy Denoyette [MVP]]

Re: Unsafe code: Converting &quot;byte *&quot; to &quot;[] byte&quot;


"_BNC" <_BNC@nospam.or g> wrote in message
news:hq2jr0dqql jj4f7m1duu4bv0i l98nv4991@4ax.c om...[color=blue]
> [re turning 'byte *' into C# '[] byte'
>
> On Thu, 9 Dec 2004 13:48:14 +0100, "Willy Denoyette [MVP]"
> <willy.denoyett e@pandora.be> wrote:
>[color=green]
>>
>>"Bob Powell [MVP]" <bob@_spamkille r_bobpowell.net > wrote in message
>>news:%23rPUwn d3EHA.3624@TK2M SFTNGP14.phx.gb l...[color=darkred]
>>> You'll need to create a byte array and copy the contents of the pointer
>>> to
>>> it.
>>>
>>> The Marshal class will enable you to do this.
>>>
>>> byte[] bytes=new byte[length];
>>> for(int i=0; i<length; i++)
>>> bytes[i]=Marshal.ReadBy te(fromPointer, i);
>>>
>>> bytes now contains the copy of the memory pointed to by fromPointer.
>>>
>>> Marshal.Copy goes the other way, from the byte array to the pointer.
>>> Shame
>>> they couldn't have written a copyfrom method.
>>>[/color]
>>
>>This has been taken care of in v2.0 using an overload of Marshal.Copy.
>>
>>Willy.[/color]
>
> The horror. Runtime is bad enough already. Is there no way to do this
> without copying bytes? I'm going through both an unmanaged C++ layer and
> then a managed C++ layer before it gets to C#. Is there a simple way to
> cast this somewhere in the C++ layers?
>
> I'm also not sure why I'd have to use 'Marshall' to copy the array. If
> I've already got a pointer and length, I could just do the copy directly,
> right? OK, I'm probably being dense.
>
>[/color]

There's no need to copy when passing managed types between C# and Managed
C++. You only should copy from managed to unmanaged memory and the other way
arround.

Willy.

[Travis]

Re: Unsafe code: Converting &quot;byte *&quot; to &quot;[] byte&quot;

I have a similar situation. C# application, unmanaged com object
(directshow filter). Using a callback function I would like to get a copy of
the data that filter has.

I've been trying:

//COM
typedef HRESULT (* MYCALLBACK) ( IMediaSample *pSample, long lSize );
HRESULT MyClass::Transf orm(IMediaSampl e *pMediaSample)
{
CheckPointer(pM ediaSample,E_PO INTER);
if(m_callback)
{
m_callback(pDes tBuffer, lSourceSize);
}
return S_OK;
}

//C#
public delegate void CallBackDelegat e(IntPtr pSample, int dataLength);
public void CallbackFunctio n(IntPtr pSample, int dataLength)
{
byte [] buffer = new byte [dataLength];
Marshal.Copy(pS ample,buffer,0, dataLength);
}

It crashes on the Marshal.Copy. Any suggestions on how to accomplish this?
I have the source for both the managed and unmanaged sides so I can change
both if necessay.


"Willy Denoyette [MVP]" wrote:
[color=blue]
>
> "_BNC" <_BNC@nospam.or g> wrote in message
> news:hq2jr0dqql jj4f7m1duu4bv0i l98nv4991@4ax.c om...[color=green]
> > [re turning 'byte *' into C# '[] byte'
> >
> > On Thu, 9 Dec 2004 13:48:14 +0100, "Willy Denoyette [MVP]"
> > <willy.denoyett e@pandora.be> wrote:
> >[color=darkred]
> >>
> >>"Bob Powell [MVP]" <bob@_spamkille r_bobpowell.net > wrote in message
> >>news:%23rPUwn d3EHA.3624@TK2M SFTNGP14.phx.gb l...
> >>> You'll need to create a byte array and copy the contents of the pointer
> >>> to
> >>> it.
> >>>
> >>> The Marshal class will enable you to do this.
> >>>
> >>> byte[] bytes=new byte[length];
> >>> for(int i=0; i<length; i++)
> >>> bytes[i]=Marshal.ReadBy te(fromPointer, i);
> >>>
> >>> bytes now contains the copy of the memory pointed to by fromPointer.
> >>>
> >>> Marshal.Copy goes the other way, from the byte array to the pointer.
> >>> Shame
> >>> they couldn't have written a copyfrom method.
> >>>
> >>
> >>This has been taken care of in v2.0 using an overload of Marshal.Copy.
> >>
> >>Willy.[/color]
> >
> > The horror. Runtime is bad enough already. Is there no way to do this
> > without copying bytes? I'm going through both an unmanaged C++ layer and
> > then a managed C++ layer before it gets to C#. Is there a simple way to
> > cast this somewhere in the C++ layers?
> >
> > I'm also not sure why I'd have to use 'Marshall' to copy the array. If
> > I've already got a pointer and length, I could just do the copy directly,
> > right? OK, I'm probably being dense.
> >
> >[/color]
>
> There's no need to copy when passing managed types between C# and Managed
> C++. You only should copy from managed to unmanaged memory and the other way
> arround.
>
> Willy.
>
>
>[/color]