WAVEOUTCAPS problem

[=?Utf-8?B?Y25pY2ts?=]

Hi,

I trying to get something that seems to be simple to work: I’m using VS
2005/C#. I want to get the information of my WaveOut devices. The WAVEOUTCAPS
structure is defined in C++ as:

typedef struct {
WORD wMid;
WORD wPid;
MMVERSION vDriverVersion;
TCHAR szPname[MAXPNAMELEN];
DWORD dwFormats;
WORD wChannels;
WORD wReserved1;
DWORD dwSupport;
} WAVEOUTCAPS;

In C# I declare it as:

public struct WAVEOUTCAPS
{
public ushort wMid;
public ushort wPid;
public ulong vDriverVersion;
public char[] szPname;
public ulong dwFormats;
public ushort wChannels;
public ushort wReserved1;
public ulong dwSupport;
}

And later in the code:

WAVEOUTCAPS waveinfo = new WAVEOUTCAPS();
waveinfo.szPnam e = new char[32];

the waveOutGetDevCa ps function is declared as

[DllImport("winm m.dll")]
public static extern int waveOutGetDevCa ps(int uDeviceID, ref WAVEOUTCAPS
lpCaps, int uSize);

everything up to here compiles and runs fine. As soon as I call

waveOutGetDevCa ps(0, ref waveinfo, Marshal.SizeOf( waveinfo));

my program crashes with the error:

System.Runtime. InteropServices .SafeArrayTypeM ismatchExceptio n was unhandled
Message="Specif ied array was not of the expected type."

Any ideas what I’m doing wrong?

[Peter Duniho]

Re: WAVEOUTCAPS problem

On Sun, 08 Jul 2007 14:00:01 -0700, cnickl
<cnickl@discuss ions.microsoft. comwrote:

[...]
my program crashes with the error:
>
System.Runtime. InteropServices .SafeArrayTypeM ismatchExceptio n was
unhandled
Message="Specif ied array was not of the expected type."
>
Any ideas what I’m doing wrong?

Maybe you need to explicitly call the Unicode version? The error sure
seems like something that would come up if you tried to pass a C# Unicode
character array to a Win32 ANSI-version function.

I think that the p/invoke stuff should have a way to specify that, but if
not I suppose you could just use "waveOutGetDevC apsW" explicitly.

Pete

[Nicholas Paldino [.NET/C# MVP]]

Re: WAVEOUTCAPS problem

The problem is that the OP has an array declaration but doesn't specify
that it should be an inline array like the original structure. The array
declaration should be:

[StructLayout(La youtKind.Sequen tial)]
public struct WAVEOUTCAPS
{
public ushort wMid;
public short wPid;
public ulong vDriverVersion;
[MarshalAs(Unman agedType.ByValT Str, SizeConst=MAXPN AMELEN)]
public string szPname;

[Peter Duniho]

Re: WAVEOUTCAPS problem

On Sun, 08 Jul 2007 16:13:12 -0700, Nicholas Paldino [.NET/C# MVP]
<mvp@spam.guard .caspershouse.c omwrote:

The problem is that the OP has an array declaration but doesn't
specify that it should be an inline array like the original structure.

Ahh. I see that now.

Is it safe to assume that p/invoke will always match up the correct TCHAR
version of a Win32 function? Or are there situations in which that is
actually an issue and needs to be addressed explicitly?

[Nicholas Paldino [.NET/C# MVP]]

Re: WAVEOUTCAPS problem

It is dependent on the value set to the CharSet property of the
StructLayout attribute assigned to the structure.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Peter Duniho" <NpOeStPeAdM@nn owslpianmk.comw rote in message
news:op.tu56tae v8jd0ej@petes-computer.local. ..

On Sun, 08 Jul 2007 16:13:12 -0700, Nicholas Paldino [.NET/C# MVP]
<mvp@spam.guard .caspershouse.c omwrote:
>

> The problem is that the OP has an array declaration but doesn't
>specify that it should be an inline array like the original structure.

>
Ahh. I see that now.
>
Is it safe to assume that p/invoke will always match up the correct TCHAR
version of a Win32 function? Or are there situations in which that is
actually an issue and needs to be addressed explicitly?

[=?Utf-8?B?Y25pY2ts?=]

Re: WAVEOUTCAPS problem

Thanks. Your post with the sample code was very helpful. I would have never
thought about this.

"Nicholas Paldino [.NET/C# MVP]" wrote:

It is dependent on the value set to the CharSet property of the
StructLayout attribute assigned to the structure.
>
>
--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m
>
"Peter Duniho" <NpOeStPeAdM@nn owslpianmk.comw rote in message
news:op.tu56tae v8jd0ej@petes-computer.local. ..

On Sun, 08 Jul 2007 16:13:12 -0700, Nicholas Paldino [.NET/C# MVP]
<mvp@spam.guard .caspershouse.c omwrote:

The problem is that the OP has an array declaration but doesn't
specify that it should be an inline array like the original structure.

Ahh. I see that now.

Is it safe to assume that p/invoke will always match up the correct TCHAR
version of a Win32 function? Or are there situations in which that is
actually an issue and needs to be addressed explicitly?

>

[Peter Duniho]

Re: WAVEOUTCAPS problem

On Sun, 08 Jul 2007 17:35:05 -0700, Nicholas Paldino [.NET/C# MVP]
<mvp@spam.guard .caspershouse.c omwrote:

It is dependent on the value set to the CharSet property of the
StructLayout attribute assigned to the structure.

I didn't see that attribute in the original post. That's my point. Can
one rely on the default behavior? Is there a reliable default behavior?
Or is a structure definition without that attribute a bug waiting to be
found?

[Chris Dunaway]

Re: WAVEOUTCAPS problem

On Jul 8, 10:18 pm, cnickl <cni...@discuss ions.microsoft. comwrote:

Thanks. Your post with the sample code was very helpful. I would have never
thought about this.
>

In the future, you might find the pinvoke.net website useful. They
also have an add in to make it easy to get pinvoke signatures directly
from VS.

Chris

[Nicholas Paldino [.NET/C# MVP]]

Re: WAVEOUTCAPS problem

Well, I would say that it is a bug. Depending on what version of the
API the OP is going to make the call for, it is up to the OP to set that
flag. Generally, when using structures for A or W versions of APIS which
have embedded strings in them which need to be marshaled (using the
ByValTStr UnmanagedType), it would be erroneous to not include the CharSet
property on the attribute definition.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Peter Duniho" <NpOeStPeAdM@nn owslpianmk.comw rote in message
news:op.tu6hp8t i8jd0ej@petes-computer.local. ..

On Sun, 08 Jul 2007 17:35:05 -0700, Nicholas Paldino [.NET/C# MVP]
<mvp@spam.guard .caspershouse.c omwrote:
>

> It is dependent on the value set to the CharSet property of the
>StructLayout attribute assigned to the structure.

>
I didn't see that attribute in the original post. That's my point. Can
one rely on the default behavior? Is there a reliable default behavior?
Or is a structure definition without that attribute a bug waiting to be
found?

[Peter Duniho]

Re: WAVEOUTCAPS problem

On Mon, 09 Jul 2007 08:14:07 -0700, Nicholas Paldino [.NET/C# MVP]
<mvp@spam.guard .caspershouse.c omwrote:

Well, I would say that it is a bug. Depending on what version of the
API the OP is going to make the call for, it is up to the OP to set that
flag. Generally, when using structures for A or W versions of APIS which
have embedded strings in them which need to be marshaled (using the
ByValTStr UnmanagedType), it would be erroneous to not include the
CharSet
property on the attribute definition.

Okay...thanks! Good to know. :)