Getting wrong byte values from C++ to C#

Asked Apr 24 '19 at 20:12

Active Apr 24 '19 at 20:12

Viewed 128 times

I'm building a plugin for Unity and looked at this answer for a method for reading byte data from C++ to C#: Passing byte array from C++ unmanaged dll to C# unity

C++ code:

char DAQ_API* Read()
    {
         char Buffer[30];
         PopulateArray(Buffer);
         return Buffer;
    }
int DAQ_API FreeMemory(char* arrayPtr) 
    {
        if (arrayPtr != nullptr) {
            delete[] arrayPtr;
        }
        return 0;
    }

C# code:

[DllImport("DAQ")]
private static extern IntPtr Read();
[DllImport("DAQ")]
public static extern int FreeMemory(IntPtr ptr);

In the update loop:

IntPtr ptr = Read();
byte[] packet = new byte[30];
Marshal.Copy(ptr, packet, 0, 30);
FreeMemory(ptr);

The size of the byte array is 30, and the first 8 bytes are correct, and the rest looks like junk data:

0 240 0 89 86 23 7 9 240 67 189 31 0 0 0 0 96 211 95 0 0 0 0 0 224 210 95 0 0 0

What's happening that's causing the bad data for the rest of the array?

asked Apr 24 '19 at 20:12

karamazovbros

2

Where is the `new []`? – tkausl Apr 24 '19 at 20:15
2

https://stackoverflow.com/a/6445794/11683 – GSerg Apr 24 '19 at 20:16
7

`char DAQ_API* Read()` -- Undefined behavior since you're returning a pointer to a local variable. When `Read` returns, that local array you declared becomes mush. – PaulMcKenzie Apr 24 '19 at 20:16
2

`if (arrayPtr != nullptr)` -- This check is not necessary. It is perfectly ok to delete a nullptr. – PaulMcKenzie Apr 24 '19 at 20:21
Thanks! That was the issue. – karamazovbros Apr 24 '19 at 21:00

Getting wrong byte values from C++ to C#

0 Answers0