How do I access the Emscripten typed array from javascript?

Question

I had compiled a C lib into javascript code by using Emscripten. However I ran into a problem when I try to bind it with my Javascript wrapper.

I wrote this to pass it by reference, I am able to access it via the compiled lib just fine.

var str_to_heapu8 = function (str) {
    return allocate(intArrayFromString(str), 'i8', ALLOC_NORMAL);
}

However, I have trouble retrieving it back to normal javascript string... the return value is an empty string.

var heapu8_to_str = function (ptr, len){
    var array = new Uint8Array(len);
    var i = 0;

    while( (ptr+i) < len){
        array[i] = getValue(ptr+i, 'i8');
        i++;
    }

    return intArrayToString(array);
}

How can I convert it back to javascript string?e

lakenen · Accepted Answer · 2013-05-23 21:30:10Z

1

This works for me:

var heapu8_to_str = function (ptr, len){
    return intArrayToString(HEAPU8.subarray(ptr, ptr+len));
};

answered May 23, 2013 at 21:30

lakenen

3,5066 gold badges30 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Eric L. · Accepted Answer · 2014-04-10 23:15:48Z

1

Emscripten (now?) provides a JavaScript function for doing this:

Pointer_stringify(ptr)

answered Apr 10, 2014 at 23:15

Eric L.

111 bronze badge

Comments

Cullen Fluffy Jennings · Accepted Answer · 2013-12-26 14:13:10Z

0

The size of the items in the buffer is 8 bytes (because the type is i8), so you need to increment the pointer value in getValue for each entry by 8. You are only increasing by 1. So the correct code would be to change the line in your code to be:

array[i] = getValue(ptr+i*8, 'i8');

answered Dec 26, 2013 at 14:13

Cullen Fluffy Jennings

9738 silver badges10 bronze badges

1 Comment

Dreamer Over a year ago

An i8 is eight bits (not bytes), which equals one byte. So your increment by eight is incorrect.

Collectives™ on Stack Overflow

How do I access the Emscripten typed array from javascript?

3 Answers 3

Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related