Passing structs in a call to a DLL

[Arnau Font]

Hi,

I'm using a DLL that has a function which receives a pointer to a struct
like this (in c++):

struct Example{
int var1;
BYTE buff[20];
char res;
}

The function:

int function (Example* ex) {
return 0;
}

I'd like to have something like this (in C#):

public struct Example {
int var1;
byte buff[20]; //Yes, it is wrong, but I want a fixed size array!
//byte[] buff; //this wouldn't be passed correctly, would it?
char res;
}


[DllImport("MyDLL.dll")]
static public extern int function(ref Example ex);

Or should I receive the structure as a byte array and convert it?

Thanks!

 

[Sergey Bogdanov]

Since the marshaller does not support array of bytes in the structure
you have to pass array of 25 bytes instead (4 bytes for int, 20 bytes
for array and 1 byte for char).

 

[Arnau Font]

Thanks Sergey! Couldn't they have done this any better?

All the DLL calls that contain structures must be done this way?

Since the marshaller does not support array of bytes in the structure
you have to pass array of 25 bytes instead (4 bytes for int, 20 bytes
for array and 1 byte for char).


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

Hi,

I'm using a DLL that has a function which receives a pointer to a struct
like this (in c++):

struct Example{
int var1;
BYTE buff[20];
char res;
}

The function:

int function (Example* ex) {
return 0;
}

I'd like to have something like this (in C#):

public struct Example {
int var1;
byte buff[20]; //Yes, it is wrong, but I want a fixed size array!
//byte[] buff; //this wouldn't be passed correctly, would it?
char res;
}


[DllImport("MyDLL.dll")]
static public extern int function(ref Example ex);

Or should I receive the structure as a byte array and convert it?

Thanks!

 

[Sergey Bogdanov]

The calls should be done in this way when a structure contains non
blittable types [1]. e.g. the following structure could be marshalled
without problems:

struct Test
{
int a;
int b;
byte c;
Rect rect;
IntPtr somePointer;
}

struct Rect
{
int x;
int y;
}

[1] "Blittable Types" table,
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetcomp/html/netcfadvinterop.asp



--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

Thanks Sergey! Couldn't they have done this any better?

All the DLL calls that contain structures must be done this way?

Since the marshaller does not support array of bytes in the structure
you have to pass array of 25 bytes instead (4 bytes for int, 20 bytes
for array and 1 byte for char).


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

Hi,

I'm using a DLL that has a function which receives a pointer to a struct
like this (in c++):

struct Example{
int var1;
BYTE buff[20];
char res;
}

The function:

int function (Example* ex) {
return 0;
}

I'd like to have something like this (in C#):

public struct Example {
int var1;
byte buff[20]; //Yes, it is wrong, but I want a fixed size array!
//byte[] buff; //this wouldn't be passed correctly, would it?
char res;
}


[DllImport("MyDLL.dll")]
static public extern int function(ref Example ex);

Or should I receive the structure as a byte array and convert it?

Thanks!

 

[Sergey Bogdanov]

sorry, gave you wrong link:
http://msdn.microsoft.com/library/en-us/dnnetcomp/html/netcfintrointerp.asp


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

The calls should be done in this way when a structure contains non
blittable types [1]. e.g. the following structure could be marshalled
without problems:

struct Test
{
int a;
int b;
byte c;
Rect rect;
IntPtr somePointer;
}

struct Rect
{
int x;
int y;
}

[1] "Blittable Types" table,
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetcomp/html/netcfadvinterop.asp




--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

Thanks Sergey! Couldn't they have done this any better?

All the DLL calls that contain structures must be done this way?

Since the marshaller does not support array of bytes in the structure
you have to pass array of 25 bytes instead (4 bytes for int, 20 bytes
for array and 1 byte for char).


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com


Arnau Font wrote:

Hi,

I'm using a DLL that has a function which receives a pointer to a
struct
like this (in c++):

struct Example{
int var1;
BYTE buff[20];
char res;
}

The function:

int function (Example* ex) {
return 0;
}

I'd like to have something like this (in C#):

public struct Example {
int var1;
byte buff[20]; //Yes, it is wrong, but I want a fixed size array!
//byte[] buff; //this wouldn't be passed correctly, would it?
char res;
}


[DllImport("MyDLL.dll")]
static public extern int function(ref Example ex);

Or should I receive the structure as a byte array and convert it?

Thanks!

 

[Peter Hartlén]

Only structures with certain complex fields, such as arrays of some kinds
(bytes, chars etc..)

Here are some links to information about this:
http://www.pinvoke.net
http://msdn.microsoft.com/library/d...ide/html/cpconblittablenon-blittabletypes.asp
http://msdn.microsoft.com/library/d.../dnnetcomp/html/ProcessManager.asp?frame=true
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetcomp/html/PInvokeLib.asp
http://www.opennetcf.org/PermaLink.aspx?guid=abe6694a-ff15-4617-a21f-8163d427a89c

There are major limitations to what Compact Framework can handle compared to
the full framework in this topic!

/ Peter

Thanks Sergey! Couldn't they have done this any better?

All the DLL calls that contain structures must be done this way?

Since the marshaller does not support array of bytes in the structure
you have to pass array of 25 bytes instead (4 bytes for int, 20 bytes
for array and 1 byte for char).


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

Hi,

I'm using a DLL that has a function which receives a pointer to a
struct
like this (in c++):

struct Example{
int var1;
BYTE buff[20];
char res;
}

The function:

int function (Example* ex) {
return 0;
}

I'd like to have something like this (in C#):

public struct Example {
int var1;
byte buff[20]; //Yes, it is wrong, but I want a fixed size array!
//byte[] buff; //this wouldn't be passed correctly, would it?
char res;
}


[DllImport("MyDLL.dll")]
static public extern int function(ref Example ex);

Or should I receive the structure as a byte array and convert it?

Thanks!

 

[Arnau Font]

Thanks a lot, Sergey!

sorry, gave you wrong link:
http://msdn.microsoft.com/library/en-us/dnnetcomp/html/netcfintrointerp.asp


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

The calls should be done in this way when a structure contains non
blittable types [1]. e.g. the following structure could be marshalled
without problems:

struct Test
{
int a;
int b;
byte c;
Rect rect;
IntPtr somePointer;
}

struct Rect
{
int x;
int y;
}

[1] "Blittable Types" table,
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetcomp/html/netcfadvinterop.asp




--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com

Thanks Sergey! Couldn't they have done this any better?

All the DLL calls that contain structures must be done this way?

"Sergey Bogdanov" <[email protected]> escribio en el mensaje

Since the marshaller does not support array of bytes in the structure
you have to pass array of 25 bytes instead (4 bytes for int, 20 bytes
for array and 1 byte for char).


--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com


Arnau Font wrote:

Hi,

I'm using a DLL that has a function which receives a pointer to a
struct
like this (in c++):

struct Example{
int var1;
BYTE buff[20];
char res;
}

The function:

int function (Example* ex) {
return 0;
}

I'd like to have something like this (in C#):

public struct Example {
int var1;
byte buff[20]; //Yes, it is wrong, but I want a fixed size array!
//byte[] buff; //this wouldn't be passed correctly, would it?
char res;
}


[DllImport("MyDLL.dll")]
static public extern int function(ref Example ex);

Or should I receive the structure as a byte array and convert it?

Thanks!