Convert args to double in NodeJS addon

Question

I would like to convert the argument 0 to a long, to use it into a dll function.

The function is defined as long function(long)

long __stdcall VBVMR_GetVoicemeeterVersion(long * pVersion);

And the call is like

void Voicemeeter_run(const FunctionCallbackInfo<Value>& args){
  Isolate* isolate = Isolate::GetCurrent();

  if (args.Length() < 1) {
    isolate->ThrowException(Exception::TypeError(
        String::NewFromUtf8(isolate, "Run needs 1 argument")));
    return;
  }

  if (!args[0]->IsNumber()) {
    isolate->ThrowException(Exception::TypeError(
        String::NewFromUtf8(isolate, "Argument 1 must be a number")));
    return;
  }

  long type = args[0]->NumberValue();
  //long type = 2;
  long value = iVMR.VBVMR_RunVoicemeeter(type);
  Local<Number> num = Number::New(isolate, value);
  args.GetReturnValue().Set(num);
}

The I got the following warning :

..\vm-wrapper.cc(101): warning C4244: 'argument' : conversion de 'double' en 'long', perte possible de données [D:\Workspace\node-voicemeter\build\vm-wrapper.vcxproj]

Is there any other Node method? If I convert is to string then convert it to long via C native function I would not loose data, right? (I do not really care for the "data loss", but I would like to get rid of the warning)

major-mann · Accepted Answer · 2015-07-16 16:50:58Z

2

You simply need to cast from double to long. You can do

double d = args[0]->NumberValue();
long l = static_cast<long>(d);

As for losing data, you will lose data if you receive a high value on output, but you can never enter a number big enough in javascript (double) to hit the upper limit of long.

edited Jul 16, 2015 at 16:50

answered Jul 15, 2015 at 14:45

major-mann

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