iOS Unity Plugin

gistfile1.c

extern "C"
{
    int _pow2(int x)
    {
        // Just a simple example of returning an int value
        return x * x;
    }
    
    // Returns a char* (a string to Unity)
    char* _helloWorldString()
    {
        // We can use NSString and go to the c string that Unity wants
        NSString *helloString = @"Hello World";
        // UTF8String method gets us a c string. Then we have to malloc a copy to give to Unity. I reuse a method below that makes it easy.
        return cStringCopy([helloString UTF8String]);
    }

    // Here is an example of getting a string from Unity
    char* _combineStrings(const char* cString1, const char* cString2)
    {
        // This shows we can create two NSStrings* from the c strings from Unity
        NSString *string1 = CreateNSString(cString1);
        NSString *string2 = CreateNSString(cString2);
        NSString *combinedString = [NSString stringWithFormat:@"%@ %@", string1, string2];
        // Same as before, have to go to a c string and then malloc a copy of it to give to Unity
        return cStringCopy([combinedString UTF8String]);
    }
}

//I also like to include these two convenience methods to convert between c string and NSString*. You need to return a copy of the c string so that Unity handles the memory and gets a valid value.

char* cStringCopy(const char* string)
{
    if (string == NULL)
        return NULL;
    
    char* res = (char*)malloc(strlen(string) + 1);
    strcpy(res, string);
    
    return res;
}

// This takes a char* you get from Unity and converts it to an NSString* to use in your objective c code. You can mix c++ and objective c all in the same file.
static NSString* CreateNSString(const char* string)
{
    if (string != NULL)
        return [NSString stringWithUTF8String:string];
    else
        return [NSString stringWithUTF8String:""];
}

Thanks for the gist. Question: wouldn't every call _helloWorldString() leak one malloc instance? If so, any suggestions on how to memory-manage those? (or is it beeing free-ed behind the scenes somehow?)

ah, no, sorry, I just read this: http://www.mono-project.com/Interop_with_Native_Libraries#Strings_as_Return_Values

chesterbr: that page seems down - but do you mean that the above code using malloc will in fact not cause memory leaks?