error LNK2001：未解析的外部符号“private：static class [英] error LNK2001: unresolved external symbol "private: static class

问题描述

错误LNK2001：未解析的外部符号private：static class irrklang :: ISoundEngine * GameEngine :: Sound :: _ soundDevice（？_soundDevice @ Sound @ GameEngine @@ 0PAVISoundEngine @ irrklang @@ A）

error LNK2001: unresolved external symbol "private: static class irrklang::ISoundEngine * GameEngine::Sound::_soundDevice" (?_soundDevice@Sound@GameEngine@@0PAVISoundEngine@irrklang@@A)

我无法弄清楚为什么我收到此错误。我相信我正确初始化。任何人可以借一只手。

I cannot figure out why i am recieving this error. I believe i am initialising correctly. Can anyone lend a hand.

sound.h

class Sound
{
private:
    static irrklang::ISoundEngine* _soundDevice;
public:
    Sound();
    ~Sound();

    //getter and setter for _soundDevice
    irrklang::ISoundEngine* getSoundDevice() { return _soundDevice; }
//  void setSoundDevice(irrklang::ISoundEngine* value) { _soundDevice = value; }
    static bool initialise();
    static void shutdown();

sound.cpp

sound.cpp

namespace GameEngine
{
Sound::Sound() { }
Sound::~Sound() { }

bool Sound::initialise()
{
    //initialise the sound engine
    _soundDevice = irrklang::createIrrKlangDevice();

    if (!_soundDevice)
    {
        std::cerr << "Error creating sound device" << std::endl;
        return false;
    }

}

void Sound::shutdown()
{
    _soundDevice->drop();
}

}

并且在那里我使用sounddevice

and where i use the sounddevice

GameEngine::Sound* sound = new GameEngine::Sound();

namespace GameEngine
{
bool Game::initialise()
{
    ///
            ... non-related code removed
            ///

    //initialise the sound engine
    if (!Sound::initialise())
        return false;

任何帮助将非常感谢。

推荐答案

将它放入 sound.cpp ：

irrklang::ISoundEngine* Sound::_soundDevice;

注意：您可能还需要初始化它，例如：

NOTE: You might want to initialize it as well, for example:

irrklang::ISoundEngine* Sound::_soundDevice = 0;

static ，但非 - const 数据成员应该在类定义之外和包含类的命名空间内定义。通常的做法是在翻译单元（ *。cpp ）中定义它，因为它被认为是一个实现细节。只有 static 和 const 整数类型可以同时声明和定义（在类定义中）：

static, but non-const data members should be defined outside of the class definition and inside the namespace enclosing the class. The usual practice is to define it in the translation unit (*.cpp) because it is considered to be an implementation detail. Only static and const integral types can be declared and defined at the same time (inside class definition):

class Example {
public:
  static const long x = 101;
};

在这种情况下，您不需要添加 x 定义，因为它已经在类定义的内部定义。但是，在你的情况下，这是必要的。从 C ++标准第9.4.2节中提取：

in this case you don't need to add x definition because it is already defined inside the class definition. However, in your case it is necessary. Extract from section 9.4.2 of the C++ Standard:

静态数据成员的定义应出现在一个包含成员类定义的命名空间范围。

The definition for a static data member shall appear in a namespace scope enclosing the member’s class definition.

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