Convert a C struct to C# (an interop problem)

[~toki]

I'm triyng to use this function
int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
(uint)Marshal.S izeOf(pSI) );

Docs say that pSI is a struct (below)
[c++]
typedef struct {
WORD wMid;
WORD wPid;
MMVERSION vDriverVersion;
CHAR szPname[MAXPNAMELEN]; // Here's the problem
WORD wTechnology;
WORD wVoices;
WORD wNotes;
WORD wChannelMask;
DWORD dwSupport;
} MIDIOUTCAPS;


This is my code in c#
[C#]
public struct MIDIOUTCAPS {
public int wMid;
public int wPid;
public long vDriverVersion;
public char[] szPname; // Here's the problem
public int wTechnology;
public int wVoices;
public int wNotes;
public int wChannelMask;
public long dwSupport;
}

MIDIOUTCAPS pSI = new MIDIOUTCAPS();
pSI.szPname = new char[32];
int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
(uint)Marshal.S izeOf(pSI) );

This code, give me a nullreference error (the callback stop in the
Kernel32.dll)

If i change "public char[] szPname; X public char szPname;" works fine
(don't retrieve the szPname) (I rename too, of course, pSI.szPname = new
char[32];)

"CHAR szPname[MAXPNAMELEN];" is a null-terminated string

Some idea?

[~toki]

Re: Convert a C struct to C# (an interop problem)

A small question should be "How can i dimension a char 'in line' (in a
structure)"


"~toki" <pedorro77.hotm ail.com> escribió en el mensaje
news:uJfmKbz9DH A.2324@tk2msftn gp13.phx.gbl...[color=blue]
> I'm triyng to use this function
> int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> (uint)Marshal.S izeOf(pSI) );
>
> Docs say that pSI is a struct (below)
> [c++]
> typedef struct {
> WORD wMid;
> WORD wPid;
> MMVERSION vDriverVersion;
> CHAR szPname[MAXPNAMELEN]; // Here's the problem
> WORD wTechnology;
> WORD wVoices;
> WORD wNotes;
> WORD wChannelMask;
> DWORD dwSupport;
> } MIDIOUTCAPS;
>
>
> This is my code in c#
> [C#]
> public struct MIDIOUTCAPS {
> public int wMid;
> public int wPid;
> public long vDriverVersion;
> public char[] szPname; // Here's the problem
> public int wTechnology;
> public int wVoices;
> public int wNotes;
> public int wChannelMask;
> public long dwSupport;
> }
>
> MIDIOUTCAPS pSI = new MIDIOUTCAPS();
> pSI.szPname = new char[32];
> int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> (uint)Marshal.S izeOf(pSI) );
>
> This code, give me a nullreference error (the callback stop in the
> Kernel32.dll)
>
> If i change "public char[] szPname; X public char szPname;" works fine
> (don't retrieve the szPname) (I rename too, of course, pSI.szPname = new
> char[32];)
>
> "CHAR szPname[MAXPNAMELEN];" is a null-terminated string
>
> Some idea?
>
>[/color]

[~toki]

Re: Convert a C struct to C# (an interop problem)

Hi ~toki, it's simple

[C#]
public struct MIDIOUTCAPS {
public int wMid;
public int wPid;
public long vDriverVersion;
[MarshalAs(Unman agedType.ByValA rray, SizeConst=32)]
public char[] szPname;
public int wTechnology;
public int wVoices;
public int wNotes;
public int wChannelMask;
public long dwSupport;
}

Regards,
~toki
:>)

"~toki" <pedorro77.hotm ail.com> escribió en el mensaje
news:%2339A5vz9 DHA.548@TK2MSFT NGP11.phx.gbl.. .[color=blue]
> A small question should be "How can i dimension a char 'in line' (in a
> structure)"
>
>
> "~toki" <pedorro77.hotm ail.com> escribió en el mensaje
> news:uJfmKbz9DH A.2324@tk2msftn gp13.phx.gbl...[color=green]
> > I'm triyng to use this function
> > int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> > (uint)Marshal.S izeOf(pSI) );
> >
> > Docs say that pSI is a struct (below)
> > [c++]
> > typedef struct {
> > WORD wMid;
> > WORD wPid;
> > MMVERSION vDriverVersion;
> > CHAR szPname[MAXPNAMELEN]; // Here's the problem
> > WORD wTechnology;
> > WORD wVoices;
> > WORD wNotes;
> > WORD wChannelMask;
> > DWORD dwSupport;
> > } MIDIOUTCAPS;
> >
> >
> > This is my code in c#
> > [C#]
> > public struct MIDIOUTCAPS {
> > public int wMid;
> > public int wPid;
> > public long vDriverVersion;
> > public char[] szPname; // Here's the problem
> > public int wTechnology;
> > public int wVoices;
> > public int wNotes;
> > public int wChannelMask;
> > public long dwSupport;
> > }
> >
> > MIDIOUTCAPS pSI = new MIDIOUTCAPS();
> > pSI.szPname = new char[32];
> > int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> > (uint)Marshal.S izeOf(pSI) );
> >
> > This code, give me a nullreference error (the callback stop in the
> > Kernel32.dll)
> >
> > If i change "public char[] szPname; X public char szPname;" works fine
> > (don't retrieve the szPname) (I rename too, of course, pSI.szPname = new
> > char[32];)
> >
> > "CHAR szPname[MAXPNAMELEN];" is a null-terminated string
> >
> > Some idea?
> >
> >[/color]
>
>[/color]

[Alison]

RE: Convert a C struct to C# (an interop problem)

Hi, Toki

I met the problem before, but slightly different from yours.
Looks like the definition of character array inside of struct MIDIOUTCAPS is supposed to specify an array size. You just declared a char array. This will not work in C#.

[Chris R]

Re: Convert a C struct to C# (an interop problem)

Try this layout.
A WORD is 16 bit (short), not 32(int). A DWORD is 32 bit(ing), not 64
(long).
Make sure to check MMVERSION and use long for 64 bit or int for 32 bit.

[color=blue]
> [C#][/color]
[StructLayout( LayoutKind.Sequ ential, CharSet=CharSet .Ansi )]
public struct MIDIOUTCAPS {
public short wMid;
public short wPid;
public long vDriverVersion; // is MMVERSION a 64 bit number?
[MarshalAs( UnmanagedType.B yValTStr, SizeConst=32 )]
public string szPname;
public short wTechnology;
public short wVoices;
public short wNotes;
public short wChannelMask;
public int dwSupport;
}

Chris R.

"~toki" <pedorro77.hotm ail.com> wrote in message
news:uJfmKbz9DH A.2324@tk2msftn gp13.phx.gbl...[color=blue]
> I'm triyng to use this function
> int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> (uint)Marshal.S izeOf(pSI) );
>
> Docs say that pSI is a struct (below)
> [c++]
> typedef struct {
> WORD wMid;
> WORD wPid;
> MMVERSION vDriverVersion;
> CHAR szPname[MAXPNAMELEN]; // Here's the problem
> WORD wTechnology;
> WORD wVoices;
> WORD wNotes;
> WORD wChannelMask;
> DWORD dwSupport;
> } MIDIOUTCAPS;
>
>
> This is my code in c#
> [C#]
> public struct MIDIOUTCAPS {
> public int wMid;
> public int wPid;
> public long vDriverVersion;
> public char[] szPname; // Here's the problem
> public int wTechnology;
> public int wVoices;
> public int wNotes;
> public int wChannelMask;
> public long dwSupport;
> }
>
> MIDIOUTCAPS pSI = new MIDIOUTCAPS();
> pSI.szPname = new char[32];
> int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> (uint)Marshal.S izeOf(pSI) );
>
> This code, give me a nullreference error (the callback stop in the
> Kernel32.dll)
>
> If i change "public char[] szPname; X public char szPname;" works fine
> (don't retrieve the szPname) (I rename too, of course, pSI.szPname = new
> char[32];)
>
> "CHAR szPname[MAXPNAMELEN];" is a null-terminated string
>
> Some idea?
>
>[/color]

[~toki]

Re: Convert a C struct to C# (an interop problem)

I found the same solution that you post.
It works now.
But i go to check the long, int & shorts.
Thanks,,


"Chris R" <sothryn@hotmai l.com> escribió en el mensaje
news:utq$AN09DH A.1496@TK2MSFTN GP09.phx.gbl...[color=blue]
> Try this layout.
> A WORD is 16 bit (short), not 32(int). A DWORD is 32 bit(ing), not 64
> (long).
> Make sure to check MMVERSION and use long for 64 bit or int for 32 bit.
>
>[color=green]
> > [C#][/color]
> [StructLayout( LayoutKind.Sequ ential, CharSet=CharSet .Ansi )]
> public struct MIDIOUTCAPS {
> public short wMid;
> public short wPid;
> public long vDriverVersion; // is MMVERSION a 64 bit number?
> [MarshalAs( UnmanagedType.B yValTStr, SizeConst=32 )]
> public string szPname;
> public short wTechnology;
> public short wVoices;
> public short wNotes;
> public short wChannelMask;
> public int dwSupport;
> }
>
> Chris R.
>
> "~toki" <pedorro77.hotm ail.com> wrote in message
> news:uJfmKbz9DH A.2324@tk2msftn gp13.phx.gbl...[color=green]
> > I'm triyng to use this function
> > int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> > (uint)Marshal.S izeOf(pSI) );
> >
> > Docs say that pSI is a struct (below)
> > [c++]
> > typedef struct {
> > WORD wMid;
> > WORD wPid;
> > MMVERSION vDriverVersion;
> > CHAR szPname[MAXPNAMELEN]; // Here's the problem
> > WORD wTechnology;
> > WORD wVoices;
> > WORD wNotes;
> > WORD wChannelMask;
> > DWORD dwSupport;
> > } MIDIOUTCAPS;
> >
> >
> > This is my code in c#
> > [C#]
> > public struct MIDIOUTCAPS {
> > public int wMid;
> > public int wPid;
> > public long vDriverVersion;
> > public char[] szPname; // Here's the problem
> > public int wTechnology;
> > public int wVoices;
> > public int wNotes;
> > public int wChannelMask;
> > public long dwSupport;
> > }
> >
> > MIDIOUTCAPS pSI = new MIDIOUTCAPS();
> > pSI.szPname = new char[32];
> > int result = NativeMethods.m idiOutGetDevCap s( -1, ref pSI,
> > (uint)Marshal.S izeOf(pSI) );
> >
> > This code, give me a nullreference error (the callback stop in the
> > Kernel32.dll)
> >
> > If i change "public char[] szPname; X public char szPname;" works fine
> > (don't retrieve the szPname) (I rename too, of course, pSI.szPname = new
> > char[32];)
> >
> > "CHAR szPname[MAXPNAMELEN];" is a null-terminated string
> >
> > Some idea?
> >
> >[/color]
>
>[/color]

[gbonnet]

Hi,

here is my code:

public short wMid;
public short wPid;
public uint vDriverVersion;
[MarshalAs(Unman agedType.ByValA rray, SizeConst=32)]
public char[] szPname;
public int dwFormats;
public short wChannels;
public short wReserved1;

It works fine!
Good luck with your project

Bye

Guillaume

http://www.ece.fr/~gbonnet