pinvoke double[] to Intptr , passing double as IntPtr ??

[Sagaert Johan]

Hi

I am struggling with pinvoke

I have dll a function that is declared as :
sf_command (IntPtr sndfile,int command, IntPtr data, int datasize);

i need to pass a pointer to a double in the data parameter, i now did :

IntPtr mem = Marshal.AllocHG lobal(sizeof(do uble));

sf_command (sndfile,comman d, mem, sizeof(double)) ;

then i did

byte[] ba=new byte[sizeof (Double)];

ba[0]=Marshal.ReadBy te(mem,0);
ba[1]=Marshal.ReadBy te(mem,1);
ba[2]=Marshal.ReadBy te(mem,2);
ba[3]=Marshal.ReadBy te(mem,3);
ba[4] = Marshal.ReadByt e(mem, 4);
ba[5] = Marshal.ReadByt e(mem, 5);
ba[6] = Marshal.ReadByt e(mem, 6);
ba[7] = Marshal.ReadByt e(mem, 7);

max_val = BitConverter.To Double(ba,0);

Marshal.FreeHGl obal(mem);


this works ,but i think there should be a shorter way ??

second question :
How do i pass an array doubles to my function ?


Johan

[Ben Voigt [C++ MVP]]

Re: pinvoke double[] to Intptr , passing double as IntPtr ??

Sagaert Johan wrote:

Hi
>
I am struggling with pinvoke
>
I have dll a function that is declared as :
sf_command (IntPtr sndfile,int command, IntPtr data, int datasize);
>
i need to pass a pointer to a double in the data parameter, i now did
:
IntPtr mem = Marshal.AllocHG lobal(sizeof(do uble));
>
sf_command (sndfile,comman d, mem, sizeof(double)) ;
>
then i did
>
byte[] ba=new byte[sizeof (Double)];
>
ba[0]=Marshal.ReadBy te(mem,0);
ba[1]=Marshal.ReadBy te(mem,1);
ba[2]=Marshal.ReadBy te(mem,2);
ba[3]=Marshal.ReadBy te(mem,3);
ba[4] = Marshal.ReadByt e(mem, 4);
ba[5] = Marshal.ReadByt e(mem, 5);
ba[6] = Marshal.ReadByt e(mem, 6);
ba[7] = Marshal.ReadByt e(mem, 7);
>
max_val = BitConverter.To Double(ba,0);
>
Marshal.FreeHGl obal(mem);
>
>
this works ,but i think there should be a shorter way ??
>
second question :
How do i pass an array doubles to my function ?

Did you try the obvious solution of using either "double[]" or "ref double"
as the type of the argument in the DllImport?

>
>
Johan

[Pavel Minaev]

Re: pinvoke double[] to Intptr , passing double as IntPtr ??

On Nov 20, 11:25 pm, "Sagaert Johan" <REMOVEsagaer.. .@hotmail.com>
wrote:

Hi
>
I am struggling with pinvoke
>
I  have dll a function that is declared as :
sf_command (IntPtr sndfile,int command, IntPtr data, int datasize);
>
i need to pass a pointer to a double in the data parameter, i now did :
>
IntPtr mem = Marshal.AllocHG lobal(sizeof(do uble));
>
sf_command (sndfile,comman d, mem, sizeof(double)) ;
>
then  i did
>
byte[] ba=new byte[sizeof (Double)];
>
ba[0]=Marshal.ReadBy te(mem,0);
ba[1]=Marshal.ReadBy te(mem,1);
ba[2]=Marshal.ReadBy te(mem,2);
ba[3]=Marshal.ReadBy te(mem,3);
ba[4] = Marshal.ReadByt e(mem, 4);
ba[5] = Marshal.ReadByt e(mem, 5);
ba[6] = Marshal.ReadByt e(mem, 6);
ba[7] = Marshal.ReadByt e(mem, 7);
>
max_val = BitConverter.To Double(ba,0);
>
Marshal.FreeHGl obal(mem);
>
this works ,but i think there should be a shorter way ??

Yes. For one thing, you can just declare the parameter as double[] in
the P/Invoke declaration for your function (or "ref double[]" if the
function is going to write some data into that array). For another,
you can use pointers:

double* p = (double*)mem;
Console.WriteLi ne(*p);

of course, this necessitates the use of "/unsafe", but there's nothing
inherently wrong about it. Pointers exist in C# for a reason, so don't
be afraid to use them for interop.

second question :
How do i pass an array doubles to my function ?
>
Johan

[Sagaert Johan]

Re: pinvoke double[] to Intptr , passing double as IntPtr ??

Hi
casting double does not work (IntPtr) double

Changing my pinvoke declaration from IntPtr to ref double is no option,
since in other case i need to pass pointer to other data type too.

I did find this is a cleaner alternative (since a double is in fact a
structure type )

IntPtr mem = Marshal.AllocHG lobal(sizeof(do uble));

int err = sf_command(Hsou ndfile, SFCommand.SFC_C ALC_NORM_SIGNAL _MAX, mem,
sizeof(double)) ; CheckError(err) ;

double max_val = (double)Marshal .PtrToStructure (mem, typeof(System.D ouble));
Marshal.FreeHGl obal(mem); return max_val;



"Ben Voigt [C++ MVP]" <rbv@nospam.nos pamwrote in message
news:u4eSVu1SJH A.5080@TK2MSFTN GP03.phx.gbl...

Sagaert Johan wrote:

>Hi
>>
>I am struggling with pinvoke
>>
>I have dll a function that is declared as :
>sf_command (IntPtr sndfile,int command, IntPtr data, int datasize);
>>
>i need to pass a pointer to a double in the data parameter, i now did
>:
>IntPtr mem = Marshal.AllocHG lobal(sizeof(do uble));
>>
>sf_command (sndfile,comman d, mem, sizeof(double)) ;
>>
>then i did
>>
>byte[] ba=new byte[sizeof (Double)];
>>
>ba[0]=Marshal.ReadBy te(mem,0);
>ba[1]=Marshal.ReadBy te(mem,1);
>ba[2]=Marshal.ReadBy te(mem,2);
>ba[3]=Marshal.ReadBy te(mem,3);
>ba[4] = Marshal.ReadByt e(mem, 4);
>ba[5] = Marshal.ReadByt e(mem, 5);
>ba[6] = Marshal.ReadByt e(mem, 6);
>ba[7] = Marshal.ReadByt e(mem, 7);
>>
>max_val = BitConverter.To Double(ba,0);
>>
>Marshal.FreeHG lobal(mem);
>>
>>
>this works ,but i think there should be a shorter way ??
>>
>second question :
>How do i pass an array doubles to my function ?

>
Did you try the obvious solution of using either "double[]" or "ref
double" as the type of the argument in the DllImport?
>

>>
>>
>Johan

>
>

[Ben Voigt [C++ MVP]]

Re: pinvoke double[] to Intptr , passing double as IntPtr ??



"Sagaert Johan" <REMOVEsagaert_ j@hotmail.comwr ote in message
news:Oy2$QpBTJH A.5056@TK2MSFTN GP04.phx.gbl...

Hi
casting double does not work (IntPtr) double
>
Changing my pinvoke declaration from IntPtr to ref double is no option,
since in other case i need to pass pointer to other data type too.

You can have multiple p/invoke declarations for the same function with
different argument lists, just like any overloaded function.