how to use byte array as parameter when calling a WindowsPhoneRuntimeComponent?

Question

First of all hey guys! I would like to access 2 C++ functions from my windows phone app. so i followed every step of this tutorial and i managed to call the function as the poster of the tutorial. Now i wanted to access my own functions so i created the class in the header and in the .cpp file and the project is building ok as long as my functions are not public. Means i cant access them.

 public ref class Base64Encoding sealed
{
  public:
    char *EncodeData(char *data, int length, int  *resultLength); //this doesnt compile
    char *DecodeString(char *data, int *resultLength); //this compiles buts inaccessible
};

i get a return exception saying error C3992: signature of public member contains invalid type char. I did some googling and as far as i understand i cannot send parameters of type char since its unmanaged code or something like that.

So what is the issue here? why i cannot pass parameters of type char?

Update

i followed robwirving suggestion and now the header looks like this.

public ref class Base64Encoding sealed
    {
    public : Platform::String^ EncodeData(String^ StringData);
    public : Platform::String^ DecodeString(String^ StringData);
    };

in order now to get char* data from the String^ StringData parameter i did in my .cpp

#include <string>
#include <iostream>
#include <msclr\marshal_cppstd.h>
using namespace Platform;
using namespace std;
String^ EncodeData(String^ StringData)
{ 
    // base64 lookup table. this is the encoding table for all 64 possible values
    static char *figures = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    msclr::interop::marshal_context context;
    std::string s = context.marshal_as<std::string>(StringData);
    char *data = new char[s.size() + 1];
    int length = s.length;
    int *resultLength = s.length;
    data[s.size()] = 0;
/* bla bla some functions irrelevant*/
.
.
.
return StringFromAscIIChars(result);
}

static String^ StringFromAscIIChars(char* chars)
{
    size_t newsize = strlen(chars) + 1;
    wchar_t * wcstring = new wchar_t[newsize];
    size_t convertedChars = 0;
    mbstowcs_s(&convertedChars, wcstring, newsize, chars, _TRUNCATE);
    String^ str = ref new Platform::String(wcstring);
    delete[] wcstring;
    return str;
}

but now i get 2 errors on building.

1: error C1114: WinRT does not support #using of a managed assembly

2: IntelliSense: an ordinary pointer to a C++/CX mapping ref class or interface class is not allowed

Answer 1

You said the answer right in your question. You can't use a char in a public function of a WinRT component. You can however use strings, I'd suggest changing your functions to the following:

public ref class Base64Encoding sealed
{
  public:
    Platform::String^ EncodeData(Platform::String^ data); 
    Platform::String^ DecodeString(Platform::String^ data);
};

In the definition of your encode/decode functions you can then convert your inputs from a Platform::String^ to a char array, call your original C++ function, then convert the return value back to a Platform::String^

I know this may seem like a lot of extra work, but it makes the interop a lot easier for the C# that will consume your WinRT component.

Update:

I think your additional errors probably come from the including msclr\marshal_cppstd.h and the way you are converting your Platform::String^ to a std::string.

Reference this post for how to convert from Platform::String^ to a char*: How to convert Platform::String to char*?