Someone has an example of how to implement a C++ function called from JS with cwrap, whose return type is a Uint8Array array?

[Lorenzo Portillo]

Someone has an example of how to implement a C++ function called from JS with cwrap, whose return type is a Uint8Array?

[J Decker]

what you might get instead is returning a pointer to some array; which is an integer, then using that integer to get a uint8array from the U8HEAP variable, using the integer as the starting offset, and whatever length you expect...

all pointers to the heap in C/C++ are really just offsets...

On Thu, Jul 21, 2022 at 5:04 PM Lorenzo Portillo <bikini...@gmail.com> wrote:

Someone has an example of how to implement a C++ function called from JS with cwrap, whose return type is a Uint8Array?

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[Lorenzo Portillo]

Thanks for the answer.

My code looks like this, but I get nothing on return.

Am I missing something?

C++

extern "C"
{
    unsigned int const* convertStringToAscii(char* text)
    {
        std::string str(text);
        unsigned int* ptr = (unsigned int*)malloc(str.size());
       
        for (int i = 0; i < str.size(); i++)
        {
            ptr[i] = int(text[i]);
        }
       
        return ptr;
    }
}

Javascript

convertStringToAscii = module.cwrap('convertStringToAscii', 'string', ['array'])
console.log(convertStringToAscii("test"))  => return empty

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[Sam Clegg]

On Thu, Jul 21, 2022 at 11:53 PM Lorenzo Portillo <bikini...@gmail.com> wrote:

Thanks for the answer.

My code looks like this, but I get nothing on return.

Am I missing something?

C++

extern "C"
{
    unsigned int const* convertStringToAscii(char* text)
    {
        std::string str(text);
        unsigned int* ptr = (unsigned int*)malloc(str.size());
       
        for (int i = 0; i < str.size(); i++)
        {
            ptr[i] = int(text[i]);
        }
       
        return ptr;
    }
}

Javascript

convertStringToAscii = module.cwrap('convertStringToAscii', 'string', ['array'])
console.log(convertStringToAscii("test"))  => return empty

The second argument to cwrap is the is the return type and the third argument are the parameter types, so I think you want do some something like `module.cwrap('convertStringToAscii', 'number', ['string'])`. 

The return type of your function is a pointer which is just a number (an offset into theheap).

El vie, 22 jul 2022 a las 2:02, J Decker (<d3c...@gmail.com>) escribió:

what you might get instead is returning a pointer to some array; which is an integer, then using that integer to get a uint8array from the U8HEAP variable, using the integer as the starting offset, and whatever length you expect...

all pointers to the heap in C/C++ are really just offsets...

On Thu, Jul 21, 2022 at 5:04 PM Lorenzo Portillo <bikini...@gmail.com> wrote:

Someone has an example of how to implement a C++ function called from JS with cwrap, whose return type is a Uint8Array?

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