Question

I have a function in C that accepts a hexadecimal parameter. I need to call this function from C#. My current approach does not seem right because my C function is returning me the wrong number.

Here is the declaration of my C function:

enum tags {
    TAG_A = -1,
    TAG_B  = 0x00, 
    TAG_C = 0xC1,  
    ...
};
int myfunction(enum tags t);

Here is my C# code:

enum tags {
    TAG_A = -1,
    TAG_B  = 0x00, 
    TAG_C = 0xC1, 
    ...
    }

[DllImport ("mylibraryname")]
    public static extern int myfunction(tags t);

myfunction(tags.TAG_B);

I am on Mac and I am using Mono and Xcode to do all of these work. The C function can be assumed correct because it’s an open-source library I downloaded. I think it’s something wrong with the hexadecimal numbers but I’m not sure.

solution:

I’ve ticked one answer, though actually setting the C# enum to long solved my problem. So in C#, I have:

enum tags : long {
TAG_A = -1,
TAG_B = 0x00,
TAG_C = 0xC1,
…
}

Answer 1

Hexadecimal is simply a different way of expressing a literal integer value. It’s irrelevant to your problem. For instance TAG_B = 0x00 and TAG_B = 0 both mean exactly the same thing.

The problem is possibly that the C enum is a 16 bit integer, whereas the C# enum is 32 bit. Instead of creating an enum in C#, try just doing it as straight Int32 values:

static class tags 
{
    public static short TAG_A = -1;
    public static short TAG_B  = 0x00;
    public static short TAG_C = 0xC1;
    // ...
}

[DllImport ("mylibraryname")]
public static extern int myfunction(short t);

myfunction(tags.TAG_B);

Or, as L.B suggested, you can just set the type of the enum members:

enum tags:short 
{
    TAG_A = -1,
    TAG_B  = 0x00, 
    TAG_C = 0xC1,
    // ...
}