I'll attempt to think before I type this time :-)
I have a a C routine I wish to call that takes the following parameters:
typedef struct XXXCB {
short a;
char b[2];
};
void scumbag(XXXCB *cb, char *v);
for our purposes v is an arbitrarily long string of bytes in the range 0x00-0x7f.
Depending on the contents of "b" variable "v" can be input to or output from the
function "scumbag".
In C# I'd code XXXCB as:
public struct XXXCB {
public short a;
[MarshalAS(UnmanagedType.ByValArray, SizeConst=2)}
public byte[] b;
}
Now, because the variable "v" can be a different length of each call (up to 32K is
size) I can't use MarshalAs(UnmanagedType.ByValArray) as mcs demands that SizeConst=
be coded (using SizeParamIndex= doesn't work, in fact I don't think it's supported).
So what I've done is created a class XXXByteBuffer to Marshal the data using
ICustomMarshaler.
Therefore, I've coded the call prototype as:
[DllImport(libname, EntryPoint = "scumbag")]
private static extern void scumbag (ref XXXCB cb,
[MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof (XXXByteBuffer))]
v);
I created the necessary methods (like ManagedToNative and NativeToManaged) in
XXXByteBuffer. When I call scumbag using parameters conforming to the above prototype
the ManagedToNative method is being driven prior to the call but NativeToManaged is
not being called on the return. If I change the prototype to specify "ref v" or "out
v" then neither method is being driven.
Neale
-----Original Message-----
I'm a little confused by your description. I am not trying to be difficult,
but you use the pronoun "it" in many places where the antecedent is unclear.
Also, the phrase "on its way out" is not clear.
Perhaps if you demonstrated the problem using a P/Invoke method with fewer
parameters and explained any problems with "in", "out", and "ref" parameters
separately, I could better understand.
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