Problem in passing arrays from C# to C++

Question

I have an application in which I need to pass an array from C# to a C++ DLL. What is the best method to do it? I did some search on Internet and figured out that I need to pass the arrays from C# using ref. The code for the same:

status = IterateCL(ref input, ref output);

The input and output arrays are of length 20. and the corresponding code in C++ DLL is

IterateCL(int *&inArray, int *&outArray)

This works fine for once. But if I try to call the function from C# in a loop the second time, the input array in C# is showing up as an array of one element. Why is this happening and please help me how I can call this function iteratively from C#.

Thanks, Rakesh.

logicnp · Accepted Answer · 2010-03-09 09:25:55Z

2

You need to use:

[DllImport("your_dll")]
public extern void IterateCL([In, MarshalAs(UnmanagedType.LPArray)] int[] arr1, [Out, MarshalAs(UnmanagedType.LPArray)] int[] arr2);

answered Mar 9, 2010 at 9:25

logicnp

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Comments

abatishchev · Accepted Answer · 2010-03-09 09:30:15Z

2

I'm not sure but try using fixed:

fixed (int* arr1 = new int[10], arr2 = new int[10])
{
            //acting with arr1 arr2 as you wish
}

Or you can use marshaling

[DllImport("your_dll")]
public extern void IterateCL([In, MarshalAs(UnmanagedType.LPArray)] int[] arr1, [Out, MarshalAs(UnmanagedType.LPArray)] int[] arr2);

edited Mar 9, 2010 at 9:30

abatishchev

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answered Mar 9, 2010 at 7:07

ILya

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4 Comments

abatishchev Over a year ago

@ILya: Yeap, it isn't necessary.

ILya Over a year ago

@abatishchev Why without OutAttribute? I thought we need to return a value from C++ to C# but InAttibute is only one direction.

abatishchev Over a year ago

As far as I understand from OP function declaration the first param is only In and the second - in Out. Though you can specify both attributes for both params but I guess it will be overuse

ILya Over a year ago

@abatishchev, Oh sure you are right! I have to read more carefully.

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