VC++编译器忽略重载函数

Question

以下是我的代码(简化)：

//wrapper.h
#include <play3d.h>
class wrapper
{
private:
    soundengine *soundEngine;
public:
    sound *playSound3D(source *source, D3DXVECTOR3 pos, bool loop=false);
};

//wrapper.cpp
sound *wrapper::playSound3D(source *source, D3DXVECTOR3 pos, bool loop)
{
    return soundEngine->play3D(source, pos, loop);
};

这是我的完整代码(根据要求)。它使用irrKlang声音引擎：

//irrKlang.h
virtual ISound* play3D(ISoundSource* source, vec3df pos,
    bool playLooped = false, 
    bool startPaused = false, 
    bool track = false,
    bool enableSoundEffects = false) = 0;//the version i want

virtual ISound* play3D(const char* soundFileName, vec3df pos,
    bool playLooped = false, 
    bool startPaused = false,
    bool track = false, 
    E_STREAM_MODE streamMode = ESM_AUTO_DETECT,
    bool enableSoundEffects = false) = 0;//the version vc++ finds


//fsCore.h
#include <irrklang.h>
class fsEngine
{
private:
    static fsEngine *instance;
    static fsBool exists;
    irrklang::ISoundEngine *soundEngine;
    fsEngine();
    ~fsEngine();
public:
    static fsEngine *getInstance()
    {
        if (!exists)
        {
            instance = new fsEngine();
            exists = true;
            return instance;
        }
        else
        {
            return instance;
        }
    };
    void release()
    {
        exists = false;
        delete instance;
        soundEngine->drop();
    };
public:
    irrklang::ISoundSource *loadSound(fsString filename);
    irrklang::ISoundSource *cloneSound(irrklang::ISoundSource *source, fsString alias=NULL);
    irrklang::ISound *playSound2D(irrklang::ISoundSource *source, fsBool loop=false);
    irrklang::ISound *playSound3D(irrklang::ISoundSource *source, D3DXVECTOR3 soundpos, fsBool loop=false);
};


//fsCore.cpp
#include "fsCore.h"
irrklang::ISound *fsEngine::playSound3D(irrklang::ISoundSource *source, D3DXVECTOR3 soundpos, bool loop)
{
    return soundEngine->play3D(source, soundpos, loop);
};

我不知从哪里得到了一部C2664 error。

1>c:\users\...\documents\visual studio 2008\projects\core\fscore.cpp(20) : error C2664: 'irrklang::ISound *irrklang::ISoundEngine::play3D(const char *,irrklang::vec3df,bool,bool,bool,irrklang::E_STREAM_MODE,bool)' : cannot convert parameter 1 from 'irrklang::ISoundSource *' to 'const char *'
1>        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

Play3D()有两个定义:一个接受'const char *'作为参数1，另一个接受'source *'作为参数1。智能感知指出了这两个定义，但我无法让VC++ 2008 express编译器识别我想要的版本。我要改变什么？

Answer 1

您的代码有两个问题，都在注释中指出。

#1，来自@john：

virtual ISound* play3D(ISoundSource* source,
    vec3df pos,
    bool playLooped = false, 
    bool startPaused = false, 
    bool track = false,
    bool enableSoundEffects = false) = 0;

irrklang::ISound *fsEngine::playSound3D(irrklang::ISoundSource *source,
                                        D3DXVECTOR3 soundpos, bool loop)
{
    return soundEngine->play3D(source, soundpos, loop);
}

调用方传递一个D3DXVECTOR3，但被调用方需要一个vec3df。它们是不同的类型，并且它们之间没有隐式转换，所以编译器会给你一些错误。在这种情况下，它给出的特定错误可能会有一点误导性。

(这两个类的大小相同并且具有相同顺序的相同数据成员，这并不重要。与how they happen to be implemented internally.无关的C++ only treats two types as equal if they equal, )

#2，来自@Named：

即使D3DXVECTOR3和vec3df是完全相同类型的typedefs，您也会遇到另一个问题。您的两个虚拟方法具有相同的名称，因此它们是重载；而且由于函数重载与虚拟重载的交互方式，子类的重载实际上隐藏了父类的版本。示例：

struct X; struct Base                  { virtual void foo(X *); };
struct Y; struct Derived : public Base { virtual void foo(Y *); };

void f(Derived *d, X *x) { d->foo(x); }


% clang++ -Wall test.cc
test.cc:2:59: warning: 'Derived::foo' hides overloaded virtual function [-Woverloaded-virtual]
    struct Y; struct Derived : public Base { virtual void foo(Y *); };
                                                          ^
test.cc:1:59: note: hidden overloaded virtual function 'Base::foo' declared here
    struct X; struct Base                  { virtual void foo(X *); };
                                                          ^
test.cc:4:39: error: cannot initialize a parameter of type 'Y *' with an lvalue of type 'X *'
    void f(Derived *d, X *x) { d->foo(x); }
                                      ^
test.cc:2:66: note: passing argument to parameter here
    struct Y; struct Derived : public Base { virtual void foo(Y *); };
                                                                 ^

解决此问题的一种方法是使用using指令：

struct X; struct Base                  { virtual void foo(X *); };
struct Y; struct Derived : public Base { virtual void foo(Y *); using Base::foo; };

void f(Derived *d, X *x) { d->foo(x); }

当我们在涉及Base::foo的上下文中查找foo时，这会将Derived重新添加到候选列表中。然而，一种更好的解决方案是对唯一功能使用唯一标识符：

struct X; struct Base                  { virtual void foox(X *); };
struct Y; struct Derived : public Base { virtual void fooy(Y *); };

void f(Derived *d, X *x) { d->foox(x); }

这里没有混淆你想要调用哪个函数-编译器没有混淆，人类读者也没有混淆。C++中的函数重载是一个用来解决特定问题的工具。If you don't have that problem, don't use that tool!