Accessing values of an unmanaged C++ pointer to pointer in C#

I want to use c++ code in my C# scripts for rendering some objects in unity 3d.

I have compiled the C++ script as a dll (lammps.dll) and have written a wrapper C# script to invoke a few functions from C++ script.

I am able to access void* and int* pointer successfully by doing the following:

Example:

  C++ prototype:

  void *lammps_extract_global(void *ptr, char *name);



  Equivalent C# prototype (in CSharpLibrary.cs file):



   DllImport("lammps.dll", EntryPoint = "lammps_extract_gloabl", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall);

   public static extern IntPtr lammps_extract_global(IntPtr ptr, [MarshalAs(UnmamanegType.LPStr)]String name);

Then I compile the C# file as a file which produces CSharpLibrary.dll

In another C# script I am using CSharpLibrary wrapper to access C++ functions as:

  1.  First define lmp_ptr as,

  var lmp_ptr = Marshal.AllocHGlobal(Marshal.Sizeof(typeof(System.IntPtr)));



  2.  Get lmp_ptr from C++ and dereference it as,

  var deref1 = (System.IntPtr)Marshal.PtrToStructure(lmp_ptr, typeof(System.IntPtr))



  3.  Then use deref1 to get natmPtr as, 

  System.IntPtr natmPtr = CSharpLibrary.CSharpLibrary.lammps_extract_global(deref1, "natoms");





   4. Convert natmPtr to an integer as,

    int nAtom = (int)Marshal.PtrToStructure(natmPtr, typeof(int))

Step 4 gives me appropriate value of nAtom.

I want to do the same thing as done for nAtom to another float pointer to pointer matrix storing positions.

   I did this to get the float pointer to pointer reference in C#

Considering lammps_extract_atom has been defined similar to the function explain above, we have

   System.IntPtr posPtr = CSharpLibrary.CSharpLibrary.lammps_extract_atom(deref1, "x")



   Here posPtr is a float** value being returned from C++

Similar statement in C++ would have looked like

  float** posPtr = (double**)(lammps_extract_atom)(void *lmp_ptr, char *name)

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

You want to return float array from C++ to C#?

– Programmer
Nov 26 '18 at 0:40

1

Create the array in C# and update it in C++. See this post. That's the most peformant way to do this. If you want to return Vector3, see this post too. Not a good idea to return non Object pointer from C++. Again, this is due to performance (memory allocation.

– Programmer
Nov 26 '18 at 0:54

1

"I cannot pass the C# array to C++ since the C++ code is quite complex" That doesn't make any sense and yes, you can. I am not sure what you mean by entry point of initialization of the array but you can can pass C# array to C++ from the Awake or Start function to initialize the array if you actually read the post I linked. If you still decide to do it your own way, don't forget to free/delete it on the C++ side and also on the C# side. Goodluck!

– Programmer
Nov 26 '18 at 4:53

1

You can use function Marshal.PtrToStruct docs.microsoft.com/en-us/dotnet/api/…

– Liu Hao
Nov 26 '18 at 9:42

1

@LiuHao Which requires GCHandle.Alloc, GCHandle.Free and freeing the array on the native just like programmer said.

– PassetCronUs
Nov 26 '18 at 21:42

|
show 2 more comments

I want to use c++ code in my C# scripts for rendering some objects in unity 3d.

I have compiled the C++ script as a dll (lammps.dll) and have written a wrapper C# script to invoke a few functions from C++ script.

I am able to access void* and int* pointer successfully by doing the following:

Example:

  C++ prototype:

  void *lammps_extract_global(void *ptr, char *name);



  Equivalent C# prototype (in CSharpLibrary.cs file):



   DllImport("lammps.dll", EntryPoint = "lammps_extract_gloabl", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall);

   public static extern IntPtr lammps_extract_global(IntPtr ptr, [MarshalAs(UnmamanegType.LPStr)]String name);

Then I compile the C# file as a file which produces CSharpLibrary.dll

In another C# script I am using CSharpLibrary wrapper to access C++ functions as:

  1.  First define lmp_ptr as,

  var lmp_ptr = Marshal.AllocHGlobal(Marshal.Sizeof(typeof(System.IntPtr)));



  2.  Get lmp_ptr from C++ and dereference it as,

  var deref1 = (System.IntPtr)Marshal.PtrToStructure(lmp_ptr, typeof(System.IntPtr))



  3.  Then use deref1 to get natmPtr as, 

  System.IntPtr natmPtr = CSharpLibrary.CSharpLibrary.lammps_extract_global(deref1, "natoms");





   4. Convert natmPtr to an integer as,

    int nAtom = (int)Marshal.PtrToStructure(natmPtr, typeof(int))

Step 4 gives me appropriate value of nAtom.

I want to do the same thing as done for nAtom to another float pointer to pointer matrix storing positions.

   I did this to get the float pointer to pointer reference in C#

Considering lammps_extract_atom has been defined similar to the function explain above, we have

   System.IntPtr posPtr = CSharpLibrary.CSharpLibrary.lammps_extract_atom(deref1, "x")



   Here posPtr is a float** value being returned from C++

Similar statement in C++ would have looked like

  float** posPtr = (double**)(lammps_extract_atom)(void *lmp_ptr, char *name)

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

You want to return float array from C++ to C#?

– Programmer
Nov 26 '18 at 0:40

1

Create the array in C# and update it in C++. See this post. That's the most peformant way to do this. If you want to return Vector3, see this post too. Not a good idea to return non Object pointer from C++. Again, this is due to performance (memory allocation.

– Programmer
Nov 26 '18 at 0:54

1

"I cannot pass the C# array to C++ since the C++ code is quite complex" That doesn't make any sense and yes, you can. I am not sure what you mean by entry point of initialization of the array but you can can pass C# array to C++ from the Awake or Start function to initialize the array if you actually read the post I linked. If you still decide to do it your own way, don't forget to free/delete it on the C++ side and also on the C# side. Goodluck!

– Programmer
Nov 26 '18 at 4:53

1

You can use function Marshal.PtrToStruct docs.microsoft.com/en-us/dotnet/api/…

– Liu Hao
Nov 26 '18 at 9:42

1

@LiuHao Which requires GCHandle.Alloc, GCHandle.Free and freeing the array on the native just like programmer said.

– PassetCronUs
Nov 26 '18 at 21:42

|
show 2 more comments

I want to use c++ code in my C# scripts for rendering some objects in unity 3d.

I have compiled the C++ script as a dll (lammps.dll) and have written a wrapper C# script to invoke a few functions from C++ script.

I am able to access void* and int* pointer successfully by doing the following:

Example:

  C++ prototype:

  void *lammps_extract_global(void *ptr, char *name);



  Equivalent C# prototype (in CSharpLibrary.cs file):



   DllImport("lammps.dll", EntryPoint = "lammps_extract_gloabl", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall);

   public static extern IntPtr lammps_extract_global(IntPtr ptr, [MarshalAs(UnmamanegType.LPStr)]String name);

Then I compile the C# file as a file which produces CSharpLibrary.dll

In another C# script I am using CSharpLibrary wrapper to access C++ functions as:

  1.  First define lmp_ptr as,

  var lmp_ptr = Marshal.AllocHGlobal(Marshal.Sizeof(typeof(System.IntPtr)));



  2.  Get lmp_ptr from C++ and dereference it as,

  var deref1 = (System.IntPtr)Marshal.PtrToStructure(lmp_ptr, typeof(System.IntPtr))



  3.  Then use deref1 to get natmPtr as, 

  System.IntPtr natmPtr = CSharpLibrary.CSharpLibrary.lammps_extract_global(deref1, "natoms");





   4. Convert natmPtr to an integer as,

    int nAtom = (int)Marshal.PtrToStructure(natmPtr, typeof(int))

Step 4 gives me appropriate value of nAtom.

I want to do the same thing as done for nAtom to another float pointer to pointer matrix storing positions.

   I did this to get the float pointer to pointer reference in C#

Considering lammps_extract_atom has been defined similar to the function explain above, we have

   System.IntPtr posPtr = CSharpLibrary.CSharpLibrary.lammps_extract_atom(deref1, "x")



   Here posPtr is a float** value being returned from C++

Similar statement in C++ would have looked like

  float** posPtr = (double**)(lammps_extract_atom)(void *lmp_ptr, char *name)

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

I want to use c++ code in my C# scripts for rendering some objects in unity 3d.

I have compiled the C++ script as a dll (lammps.dll) and have written a wrapper C# script to invoke a few functions from C++ script.

I am able to access void* and int* pointer successfully by doing the following:

Example:

  C++ prototype:

  void *lammps_extract_global(void *ptr, char *name);



  Equivalent C# prototype (in CSharpLibrary.cs file):



   DllImport("lammps.dll", EntryPoint = "lammps_extract_gloabl", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall);

   public static extern IntPtr lammps_extract_global(IntPtr ptr, [MarshalAs(UnmamanegType.LPStr)]String name);

Then I compile the C# file as a file which produces CSharpLibrary.dll

In another C# script I am using CSharpLibrary wrapper to access C++ functions as:

  1.  First define lmp_ptr as,

  var lmp_ptr = Marshal.AllocHGlobal(Marshal.Sizeof(typeof(System.IntPtr)));



  2.  Get lmp_ptr from C++ and dereference it as,

  var deref1 = (System.IntPtr)Marshal.PtrToStructure(lmp_ptr, typeof(System.IntPtr))



  3.  Then use deref1 to get natmPtr as, 

  System.IntPtr natmPtr = CSharpLibrary.CSharpLibrary.lammps_extract_global(deref1, "natoms");





   4. Convert natmPtr to an integer as,

    int nAtom = (int)Marshal.PtrToStructure(natmPtr, typeof(int))

Step 4 gives me appropriate value of nAtom.

I want to do the same thing as done for nAtom to another float pointer to pointer matrix storing positions.

   I did this to get the float pointer to pointer reference in C#

Considering lammps_extract_atom has been defined similar to the function explain above, we have

   System.IntPtr posPtr = CSharpLibrary.CSharpLibrary.lammps_extract_atom(deref1, "x")



   Here posPtr is a float** value being returned from C++

Similar statement in C++ would have looked like

  float** posPtr = (double**)(lammps_extract_atom)(void *lmp_ptr, char *name)

c# c++ unity3d marshalling unmanaged

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

asked Nov 26 '18 at 0:09

Ankit Mishra

132113

You want to return float array from C++ to C#?

– Programmer
Nov 26 '18 at 0:40

1

Create the array in C# and update it in C++. See this post. That's the most peformant way to do this. If you want to return Vector3, see this post too. Not a good idea to return non Object pointer from C++. Again, this is due to performance (memory allocation.

– Programmer
Nov 26 '18 at 0:54

1

"I cannot pass the C# array to C++ since the C++ code is quite complex" That doesn't make any sense and yes, you can. I am not sure what you mean by entry point of initialization of the array but you can can pass C# array to C++ from the Awake or Start function to initialize the array if you actually read the post I linked. If you still decide to do it your own way, don't forget to free/delete it on the C++ side and also on the C# side. Goodluck!

– Programmer
Nov 26 '18 at 4:53

1

You can use function Marshal.PtrToStruct docs.microsoft.com/en-us/dotnet/api/…

– Liu Hao
Nov 26 '18 at 9:42

1

@LiuHao Which requires GCHandle.Alloc, GCHandle.Free and freeing the array on the native just like programmer said.

– PassetCronUs
Nov 26 '18 at 21:42

|
show 2 more comments

You want to return float array from C++ to C#?

– Programmer
Nov 26 '18 at 0:40

1

Create the array in C# and update it in C++. See this post. That's the most peformant way to do this. If you want to return Vector3, see this post too. Not a good idea to return non Object pointer from C++. Again, this is due to performance (memory allocation.

– Programmer
Nov 26 '18 at 0:54

1

"I cannot pass the C# array to C++ since the C++ code is quite complex" That doesn't make any sense and yes, you can. I am not sure what you mean by entry point of initialization of the array but you can can pass C# array to C++ from the Awake or Start function to initialize the array if you actually read the post I linked. If you still decide to do it your own way, don't forget to free/delete it on the C++ side and also on the C# side. Goodluck!

– Programmer
Nov 26 '18 at 4:53

1

You can use function Marshal.PtrToStruct docs.microsoft.com/en-us/dotnet/api/…

– Liu Hao
Nov 26 '18 at 9:42

1

@LiuHao Which requires GCHandle.Alloc, GCHandle.Free and freeing the array on the native just like programmer said.

– PassetCronUs
Nov 26 '18 at 21:42

You want to return float array from C++ to C#?

– Programmer
Nov 26 '18 at 0:40

Create the array in C# and update it in C++. See this post. That's the most peformant way to do this. If you want to return Vector3, see this post too. Not a good idea to return non Object pointer from C++. Again, this is due to performance (memory allocation.

– Programmer
Nov 26 '18 at 0:54

"I cannot pass the C# array to C++ since the C++ code is quite complex" That doesn't make any sense and yes, you can. I am not sure what you mean by entry point of initialization of the array but you can can pass C# array to C++ from the Awake or Start function to initialize the array if you actually read the post I linked. If you still decide to do it your own way, don't forget to free/delete it on the C++ side and also on the C# side. Goodluck!

– Programmer
Nov 26 '18 at 4:53

You can use function Marshal.PtrToStruct docs.microsoft.com/en-us/dotnet/api/…

– Liu Hao
Nov 26 '18 at 9:42

@LiuHao Which requires GCHandle.Alloc, GCHandle.Free and freeing the array on the native just like programmer said.

– PassetCronUs
Nov 26 '18 at 21:42

|
show 2 more comments

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