Tips for using a C library from C#

Question

I\'ve got a library in C which I\'d like to use from C#.

From what I\'ve gleaned off the internet, one idea is to wrap it in a C++ dll, and DllImport that.

Answer 1

Here is a way to send a LOT of numeric data to your C function via a StringBuilder. Just dump your numbers in a StringBuilder, while setting delimiters at appropriate positions et voilá:

class Program
    {  
        [DllImport("namEm.DLL", CallingConvention = CallingConvention.Cdecl, EntryPoint = "nameEm", 
            CharSet = CharSet.Ansi, BestFitMapping = false, ThrowOnUnmappableChar = true)]
        public static extern int nameEm([MarshalAs(UnmanagedType.LPStr)] StringBuilder str);
        static void Main(string[] args)
        {
            int m = 3;
            StringBuilder str = new StringBuilder();
            str.Append(String.Format("{0};", m));
            str.Append(String.Format("{0} {1:E4};", 5, 76.334E-3 ));
            str.Append(String.Format("{0} {1} {2} {3};", 65,45,23,12));
            m = nameEm(str);
        }
    }

And at C-side, pick up the StringBuilder as a char*:

extern "C"
{
    __declspec(dllexport) int __cdecl nameEm(char* names)
    {
        int n1, n2, n3[4];
        char *token,
             *next_token2 = NULL,
             *next_token = NULL;
        float f;

        sscanf_s(strtok_s(names, ";", &next_token), "%d", &n2);
        sscanf_s(strtok_s(NULL, ";", &next_token), "%d %f", &n1, &f);
        // Observe the use of two different strtok-delimiters.
        // the ';' to pick the sequence of 4 integers,
        // and the space to split that same sequence into 4 integers.
        token = strtok_s(strtok_s(NULL, ";", &next_token)," ",&next_token2);
        for (int i=0; i < 4; i++)
        {
             sscanf_s(token,"%d", &n3[i]);
             token = strtok_s(NULL, " ",&next_token2);
        }    
        return 0;
    }
}