Export a 'long' from unmanaged code into .net

GerhardKreuzer

Hi, I have to export a 'long' value from an unmanaged dll to a VB app. I do this with other data types like int and bool, works fine, so I more or less know how do do it. When I do the same with 'long' the call crashes. Where there any samples out? What is so special with 'long'? Thanks for helping. With best regards Gerhard

extern "C" { __declspec(dllexport) long GetCurrentFileRawFilePointer (void); }
extern "C" { __declspec(dllexport) int AwaitCycleDoneFor (uint); }
extern "C" { __declspec(dllexport) bool isDataLinkClear (void); }

First line fails, other worked fine.

Declare Function GetCurrentFileRawFilePointer Lib "GeoMon4D_iMX7.dll" () As Long
Declare Function AwaitCycleDoneFor Lib "GeoMon4D_iMX7.dll" (timeout_ms As UInteger) As Integer
Declare Function isDataLinkClear Lib "GeoMon4D_iMX7.dll" () As Boolean

Jeremy Falcon

GerhardKreuzer wrote:

extern "C" { __declspec(dllexport) bool isDataLinkClear (void); }

It's because of the extra spaces in this line.

Jeremy Falcon

OriginalGriff

It's a long value, but the VB code requires a short - so you will need to zip the value - which should compress it nicely - and then pass it.

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!

Shuqian Ying

I used C/C++ many years ago, as I recall that the long in C/C++ is actually 32 bits, the 64 bits type is called long long (or something like it), whereas long in .NET (and many other later languages) is 64 bits (see [here](<code>long</code>)[[^](<code>long</code>)]).

englebart

If none of the other approaches work, consider a struct. struct MyLong { int hi; int lo; } In the C/C++ side you might be able to union with a long, but it is probably more platform portable to explicitly crack the long and assign the two members separately.

PIEBALDconsult

Better to remove the zero-bits because they are worthless anyway.

Shao Voon Wong

Your long is actually a pointer. A pointer is unsigned 4 bytes or 8 bytes on 32-bit and 64-bit platform respectively. Long is always signed 64-bit integer on .NET. And you are not supposed to use a native file pointer in .NET to read/write to a file. Restrict your file operations to native code.

extern "C" { __declspec(dllexport) void* GetCurrentFileRawFilePointer (void); }

Declare Function GetCurrentFileRawFilePointer Lib "GeoMon4D_iMX7.dll" () As IntPtr

k5054

Many years ago, true (mostly). Today, at least on the 64 bit Archs (x86-64, arm-64, risc-v-64) I'm aware of, a long is 64 bits, as is a long long. And going back even further in time (8086 days), an int was 16 bits, and longs and long longs were 32 bits.

Keep Calm and Carry On

Shuqian Ying

so they are referring to kind of physical unit rather than logical unit ...

Kate X257

This is the way to do it. You could cast it, but it's never going to be as easy, safe and predictable as using a struct.

OriginalGriff

This is the way. :RemovesHelmet:

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!

jschell

In C++ and probably C the type is going to be 'int64_t'. That is exactly 64 bits in all situations.

englebart

My other option was struct MyLong { int hi; uint lo; } You only need the sign in one spot. Am I right? :Reapplies Helmet: ? :Puts Helmet on head and fastens chin strap and lowers visor: ? What is the opposite of “Removes Helmet” that is just as concise?

OriginalGriff

englebart wrote:

What is the opposite of “Removes Helmet” that is just as concise?

"Equips helmet"?

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!

englebart

I like it. Reminds me of a text based dungeon game!

GerhardKreuzer

Hi, lastly I found a working solution and its far from zipping data, thanks for that really good idea, but it was not April 1st, (and gives insight into your mindset). The embedded framework didn't support passing 64 bit values between managed and unmanaged code. A little workaround is needed. Fist create a new IntPnt object and pass this object to unmanged code by reference as parameter of some function. In unmanaged code use this pointer as any other pointer in C/C++, and assign the data you need. Return from this unmanaged function and use the 'Marshal' class to readout the value. Use a 'try finally' block to clean up memory in any case. Managed code:

Private Shared Function ReadFilePointer() As Long
Dim ptr As IntPtr = Marshal.AllocHGlobal(Len(New Long()))
Try
GetBookmark(ptr)
Return Marshal.ReadInt64(ptr)
Finally
Marshal.FreeHGlobal(ptr)
End Try
End Function

Unmanaged code:

extern "C" { __declspec(dllexport) void GetBookmark (intptr_t*); }

void GetBookmark(intptr_t* bmark)
{
*bmark = ftell(outFile);
}

Hope this can help someone someday. With best regards Gerhard

Kate X257

your reasoning is sound, for one type of bit ordering I'd personally stick to int and unit test the conversion logic instead the details are easier to work out that way