How to use vectors (of C++ STL) with WebAssembly

问题

#include <iostream>
#include<vector>
using namespace std;

vector<int> ver;

int pushData(int n)
{
    for(int i=0;i<n;i++)
    {
        ver.push_back(i);
    }
}

I want to call pushData function from JS and push some data to vector "ver" and use it later. please explain how to do that using WebAssembly.

回答1:

I tried to answer your question, by using this answer: https://stackoverflow.com/a/46748966/544721

to make solution :

#include<vector>
const int SIZE = 10;
std::vector<int> data(10);

void add(int value) { 
  for (int i=0; i<SIZE; i++) {
    data[i] = data[i] + value;
  }
}

int* getData() {
  return &(data[0]);
}

and js:

var wasmModule = new WebAssembly.Module(wasmCode);
var wasmInstance = new WebAssembly.Instance(wasmModule, wasmImports);

var offset = wasmInstance.exports.getData();

var linearMemory = new Uint32Array(wasmInstance.exports.memory.buffer, offset, 10);
for (var i = 0; i < linearMemory.length; i++) {
  linearMemory[i] = i;
}

wasmInstance.exports.add(10);

for (var i = 0; i < linearMemory.length; i++) {
  log(linearMemory[i]);
}

WasmFiddle: https://wasdk.github.io/WasmFiddle//?wuycy

But it looks like there is some linker error:

line 2: Uncaught LinkError: WebAssembly Instantiation: Import #9 module="env" function="__dso_handle" error: global import must be a number

Can anyone help to make this C++ code to run in WasmFiddle?

回答2:

i'm do something like you.In my opinion, using STL in WASM is very difficult.

My solution is to create a simulate vector.Wasm only supports int32, int64, float32 and float64 and wasm's adderess is differnt from other process.So it is not feasible to import the library directly. You can call the library function through a proxy or conversion.Or you can write it by yourself.

In this case, vector can't be imported directly.You can create a class named vector,and implement the push_back function.

class vector{
public:
    bool push_back(int i){
       // do something
    }
    int& at(uint index){
       // do something
    }
private:
    int* int_ptr;
}

More details here https://aransentin.github.io/cwasm/

来源：https://stackoverflow.com/questions/50220966/how-to-use-vectors-of-c-stl-with-webassembly

标签

c++14

webassembly