I have a C++ project that is intended to perform some calculations. The C++ code will sit on a server that as back end to a browser based GUI. Node.js seems to be suitable for this job. I've gone through the tutorials and learnt to build C++ code to be used as a nodejs module.
For the sake of simplicity, I'd like to compile the C++ code as a static library. I could then write a C++ class which references this library which can then be used in the nodejs environment. The point of this is so I don't have to use node-gyp build to build my entire C++ project. This way I can further develop the C++ code without worrying too much about the front end.
To achieve this, I have done the following:
Built a simple C++ library as follows. Building this in Visual Studio 2013 to get the .lib file.
//MyClass.h #pragma once class MyClass { public: double Multiply(double a, double b) { return a*b; } MyClass(); ~MyClass(); };Created the C++ object to be used as a nodejs module like so:
// myobject.h #ifndef MYOBJECT_H #define MYOBJECT_H #include <node.h> #include <node_object_wrap.h> #include "MyLib\MyClass.h" namespace demo { class MyObject : public node::ObjectWrap { public: static void Init(v8::Local<v8::Object> exports); static MyClass* mycalcobj; private: explicit MyObject(double value = 0); ~MyObject(); static void New(const v8::FunctionCallbackInfo<v8::Value>& args); static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args); static v8::Persistent<v8::Function> constructor; double value_; }; } // namespace demo #endifand the cpp file
// myobject.cpp #include "myobject.h" //#include "worker.h" namespace demo { using v8::Function; using v8::FunctionCallbackInfo; using v8::FunctionTemplate; using v8::Isolate; using v8::Local; using v8::Number; using v8::Object; using v8::Persistent; using v8::String; using v8::Value; Persistent<Function> MyObject::constructor; MyObject::MyObject(double value) : value_(value) { } MyObject::~MyObject() { } void MyObject::Init(Local<Object> exports) { Isolate* isolate = exports->GetIsolate(); // Prepare constructor template Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New); tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject")); tpl->InstanceTemplate()->SetInternalFieldCount(1); // Prototype NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne); constructor.Reset(isolate, tpl->GetFunction()); exports->Set(String::NewFromUtf8(isolate, "MyObject"), tpl->GetFunction()); } void MyObject::New(const FunctionCallbackInfo<Value>& args) { Isolate* isolate = args.GetIsolate(); if (args.IsConstructCall()) { // Invoked as constructor: `new MyObject(...)` double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue(); MyObject* obj = new MyObject(value); obj->Wrap(args.This()); args.GetReturnValue().Set(args.This()); } else { // Invoked as plain function `MyObject(...)`, turn into construct call. const int argc = 1; Local<Value> argv[argc] = { args[0] }; Local<Function> cons = Local<Function>::New(isolate, constructor); args.GetReturnValue().Set(cons->NewInstance(argc, argv)); } } //define functions here void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) { Isolate* isolate = args.GetIsolate(); MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder()); double x = obj->value_; mycalcobj = new MyClass(); x=mycalcobj->Multiply(2, x); obj->value_= x; args.GetReturnValue().Set(Number::New(isolate, obj->value_)); } } // namespace demoCreate the main cpp file to initialise
#include <node.h> #include "myobject.h" namespace demo { using v8::Local; using v8::Object; void InitAll(Local<Object> exports) { MyObject::Init(exports); } NODE_MODULE(addon, InitAll) } // namespace demoThe binding.gyp file is defined as:
{ "targets": [ { "target_name": "cpphello", "sources": [ "cpphello.cpp", "myobject.cpp"], "libraries": [ "D:/East101/Adri/javascript/socketio/cpplib/build/x64/Debug/MyLib"] } ] }Build the project using node-gyp configure build
I get the following messages:
MyLib.lib(MyClass.obj) : warning LNK4075: ignoring '/EDITANDCONTINUE' due to '/OPT:ICF' specification [D:\East101\Adri\javascript\socketio\cpplib\build\cpphello.vcxproj]
LINK : warning LNK4098: defaultlib 'MSVCRTD' conflicts with use of other libs;use /NODEFAULTLIB:library [D:\East101\Adri\javascript\socketio\cpplib\build\cpphello.vcxproj]
myobject.obj : error LNK2001: unresolved external symbol "public: static class MyClass * demo::MyObject::mycalcobj" (?mycalcobj@MyObject@demo@@2PEAVMyClass@@EA) [D:\East101\Adri\javascript\socketio\cpplib\build\cpphello.vcxproj] D:\East101\Adri\javascript\socketio\cpplib\build\Release\cpphello.node : fatal error LNK1120: 1 unresolved externals [D:East101\Adri\javascript\socketio\cpplib\build\cpphello.vcxproj]
I need some assistance to either fix this error and make it work as I envision it or let me know if there's a better way. I'm quite new to C++ and coding in general so I may just be approaching this wrong.