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ViewsHow to make this code safe when accessing DLL?
To return arrays in C pointers needed. To clarify my question, I created a simple .c function and compiled as DLL and accessing it by C#. The C function is:
#include <stdio.h>
__declspec(dllexport) int* ReturnArray(int size) {
int* arr = malloc(size * sizeof(int));
arr[0] = 19;
arr[1] = 18;
arr[2] = 17;
arr[3] = 16;
arr[4] = 15;
return arr;
}
On the C# side:
namespace ConsoleC2CSExample
{
class Program
{
[DllImport("array.dll", EntryPoint = "ReturnArray", CallingConvention = CallingConvention.Cdecl)]
public unsafe static extern short* ReturnArray(int size);
static unsafe void Main(string[] args)
{
int arraySize = 5;
short *ptr = ReturnArray(arraySize);
for(int i = 0; i < arraySize; i++)
Console.WriteLine(*(ptr + i * sizeof(short)));
Console.Read();
}
}
}
And the output is as expected as follows:
I have two questions here.
- How can this be done by not using unsafe mode?
- And what are the dangers if any of using unsafe?
1 answers
Answer question0
C#/.NET is so-called managed code because it runs safely on the common language runtime (CLR). Whereas, C code is so-called unmanaged code.
The CLR ensures, that we will not suffer the typical problems known from C code (like buffer underflow, buffer overflow, ...) resulting in vulnerable code, crashing applications, unknown behavior, etc.
So the danger of using unsafe code is, that errors in your C library will probably terminate your entire C#/.NET application unexpectedly, causing you a lot of headache.
To get at least rid of the unsafe context within your C# code, you can try the following:
using System.Runtime.InteropServices;
namespace ConsoleC2CSExample
{
class Program
{
[DllImport("array.dll", EntryPoint = "ReturnArray", CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr ReturnArray(int size);
static void Main(string[] args)
{
int arraySize = 5;
IntPtr ptr = ReturnArray(arraySize);
for(int i = 0; i < arraySize; i++)
Console.WriteLine(Marshal.ReadInt32(ptr + i * sizeof(int)));
Console.Read();
}
}
}