How to get IntPtr from byte in C

Question

I want to pass a byte   to a method takes a IntPtr Parameter in C   is that possible and how

User · Answer

You could use Marshal UnsafeAddrOfPinnedArrayElement to get a memory pointer to the array  or to a specific element in the array   Keep in mind that the array must be pinned first as per the API documentation   The array must be pinned using a GCHandle before it is passed to this method  For maximum performance  this method does not validate the array passed to it  this can result in unexpected behavior

User · Answer

This should work but must be used within an unsafe context   byte   buffer   new byte 255   fixed  byte  p   buffer        IntPtr ptr    IntPtr p         do you stuff here     beware  you have to use the pointer in the fixed block  The gc can move the object once you are not anymore in the fixed block

User · Answer

IntPtr GetIntPtr Byte   byteBuf        IntPtr ptr   Marshal AllocHGlobal byteBuf Length       for  int i   0  i  lt  byteBuf Length  i                 Marshal WriteByte ptr  i  byteBuf i              return ptr

User · Answer

Here s a twist on  user65157 s answer   1 for that  BTW    I created an IDisposable wrapper for the pinned object   class AutoPinner   IDisposable      GCHandle  pinnedArray     public AutoPinner Object obj              pinnedArray   GCHandle Alloc obj  GCHandleType Pinned           public static implicit operator IntPtr AutoPinner ap             return ap  pinnedArray AddrOfPinnedObject             public void Dispose               pinnedArray Free             then use it like thusly   using  AutoPinner ap   new AutoPinner MyManagedObject        UnmanagedIntPtr   ap      Use the operator to retrieve the IntPtr      do your stuff     I found this to be a nice way of not forgetting to call Free

User · Answer

In some cases you can use an Int32 type  or Int64  in case of the IntPtr  If you can  another useful class is BitConverter  For what you want you could use BitConverter ToInt32 for example

User · Answer

Not sure about getting an IntPtr to an array  but you can copy the data for use with unmanaged code by using Mashal Copy   IntPtr unmanagedPointer   Marshal AllocHGlobal bytes Length   Marshal Copy bytes  0  unmanagedPointer  bytes Length      Call unmanaged code Marshal FreeHGlobal unmanagedPointer     Alternatively you could declare a struct with one property and then use Marshal PtrToStructure  but that would still require allocating unmanaged memory   Edit  Also  as Tyalis pointed out  you can also use fixed if unsafe code is an option for you

User · Answer

Marshal Copy works but is rather slow  Faster is to copy the bytes in a for loop  Even faster is to cast the byte array to a ulong array  copy as much ulong as fits in the byte array  then copy the possible remaining 7 bytes  the trail that is not 8 bytes aligned   Fastest is to pin the byte array in a fixed statement as proposed above in Tyalis  answer

User · Answer

Another way   GCHandle pinnedArray   GCHandle Alloc byteArray  GCHandleType Pinned   IntPtr pointer   pinnedArray AddrOfPinnedObject       Do your stuff    pinnedArray Free

[c#] How to get IntPtr from byte[] in C#

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