如何在 Node.js 的 C++ 插件中使用 std::string? [英] How do I use std::string in a C++ Addon for Node.js?

问题描述

我正在尝试按照此处的 node.js 文档包装用于 javascript 的 C++ 对象:https://nodejs.org/api/addons.html#addons_wrapping_c_objects

I'm trying to wrap C++ objects for use in javascript as per the node.js documentation here: https://nodejs.org/api/addons.html#addons_wrapping_c_objects

当我的对象AnObject"只有数字属性，即int32_t age;"时，插件可以无误地构建，并且可以正常工作.

The Addon would build without error, and work properly when my object "AnObject" only had numeric attributes i.e "int32_t age;".

当我添加属性std::string name;"时对于 AnObject，node-gyp 配置"有效，但是node-gyp 构建"出现以下错误:

When I added the attribute "std::string name;" to AnObject, "node-gyp configure" worked, however "node-gyp build" gave the following error:

Wills-MacBook-Pro:cppObjectWrapping willalley$ node-gyp build
[...]
In file included from ../personAddon.cc:3:
../AnObject.h:24:21: error: implicit instantiation of undefined template 
'std::basic_string<char, std::char_traits<char>,
      std::allocator<char> >'
        std::string name;
                    ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs
/MacOSX10.12.sdk/usr/include/c++/4.2.1/bits/stringfwd.h:56:11: note: 
      template is declared here
    class basic_string;
          ^
1 error generated.
[...]
Wills-MacBook-Pro:cppObjectWrapping willalley$

这是我抛出错误的对象头文件，AnObject.h:

Here is my objects header file where the error is thrown, AnObject.h:

    #pragma once

    #include <node.h>
    #include <node_object_wrap.h>
    #include <string.h>

    namespace demo {

        class AnObject : public node::ObjectWrap {
        public:
            static void Init(v8::Local<v8::Object> exports);

        private:
            explicit AnObject(int32_t num = 19);
            ~AnObject();

            static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
            static void setAge(const v8::FunctionCallbackInfo<v8::Value>& args);
            static void getAge(const v8::FunctionCallbackInfo<v8::Value>& args);
            static void setName(const v8::FunctionCallbackInfo<v8::Value>& args);
            static void getName(const v8::FunctionCallbackInfo<v8::Value>& args);
            static v8::Persistent<v8::Function> constructor;
            int32_t age;
            std::string name;
        };

    }  // namespace demo

如果你好奇，实现文件 AnObject.cc:

and if you're curious, the implementation file AnObject.cc:

#include "AnObject.h"
#include <string.h>

namespace demo {

    using v8::Context;
    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> AnObject::constructor;

    AnObject::AnObject(int32_t age_) : age(age_) {
    }

    AnObject::~AnObject() {
    }

    void AnObject::Init(Local<Object> exports) {
        Isolate* isolate = exports->GetIsolate();

        // Prepare constructor template
        Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
        tpl->SetClassName(String::NewFromUtf8(isolate, "AnObject"));
        tpl->InstanceTemplate()->SetInternalFieldCount(1);

        // Prototype
        NODE_SET_PROTOTYPE_METHOD(tpl, "setAge", setAge);
        NODE_SET_PROTOTYPE_METHOD(tpl, "setName", setName);
        NODE_SET_PROTOTYPE_METHOD(tpl, "getAge", getAge);
        NODE_SET_PROTOTYPE_METHOD(tpl, "getName", getName);

        constructor.Reset(isolate, tpl->GetFunction());
        exports->Set(String::NewFromUtf8(isolate, "AnObject"),
                     tpl->GetFunction());
    }

    void AnObject::New(const FunctionCallbackInfo<Value>& args) {
        Isolate* isolate = args.GetIsolate();

        if (args.IsConstructCall()) {
            // Invoked as constructor: `new AnObject(...)`
            int32_t value = args[0]->IsUndefined() ? 0 : args[0]->Int32Value();;
            AnObject* obj = new AnObject(value);
            obj->Wrap(args.This());
            args.GetReturnValue().Set(args.This());
        } else {
            // Invoked as plain function `AnObject(...)`, turn into construct call.
            const int argc = 1;
            Local<Value> argv[argc] = { args[0] };
            Local<Context> context = isolate->GetCurrentContext();
            Local<Function> cons = Local<Function>::New(isolate, constructor);
            Local<Object> result =
            cons->NewInstance(context, argc, argv).ToLocalChecked();
            args.GetReturnValue().Set(result);
        }
    }

    void AnObject::setAge(const FunctionCallbackInfo<Value>& args) {
        Isolate* isolate = args.GetIsolate();
        AnObject* obj = ObjectWrap::Unwrap<AnObject>(args.Holder());
        if (args[0]->IsInt32()){
            obj->age = args[0]->Int32Value();
            args.GetReturnValue().Set(Number::New(isolate, obj->age));
        }
    }

    void AnObject::setName(const v8::FunctionCallbackInfo<v8::Value>& args) {
        Isolate* isolate = args.GetIsolate();
        AnObject* obj = ObjectWrap::Unwrap<AnObject>(args.Holder());

        if (args[0]->isString()) {
            std::string input(*v8::String::Utf8Value(args[0]->ToString()));
            obj->name = input;
            args.GetReturnValue().Set(Number::New(isolate, obj->name));
        }
    }

    void AnObject::getAge(const FunctionCallbackInfo<Value>& args) {
        Isolate* isolate = args.GetIsolate();
        AnObject* obj = ObjectWrap::Unwrap<AnObject>(args.Holder());
        args.GetReturnValue().Set(Number::New(isolate, obj->age));
    }

    void AnObject::getName(const FunctionCallbackInfo<Value>& args) {
        Isolate* isolate = args.GetIsolate();
        AnObject* obj = ObjectWrap::Unwrap<AnObject>(args.Holder());
        v8::Local<v8::String> output = v8::String::NewFromUtf8(isolate, name.cstr());
        args.GetReturnValue().Set(Number::New(isolate, output));
    }

}  // namespace demo

推荐答案

我发现的值得一看的解决方案是:

The face-palm worthy solution I found is:

改变:

#include <string.h>

到:

#include <string>

在 AnObject.h 和 AnObject.cc 中

in both AnObject.h and AnObject.cc

这篇关于如何在 Node.js 的 C++ 插件中使用 std::string?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！