定製UniformRandomBitGenerator編譯失敗

Question

我試圖創建一個圍繞在C++頭定義的隨機數生成源返回uint_fast32_t的包裝，使得一個基類可以存儲指向任何RNG（標準:: mt19937，性病:: default_random等）。這是爲了將隨機數生成源存儲爲類成員，而不必將該類作爲模板類。我提出的解決方案是：我定義了一個抽象基類RNGSource，它實現了C++ UniformRandomBitGenerator標準。然後，我所定義的模板類RNGSourceWrap實現RNGSource，需要一些C++ RNG源作爲參數，並且實現RNGSource功能轉發到底層C++ RNG存儲呼叫。的代碼如下：

#ifndef RANDOM_H 
#define RANDOM_H 
#include <cstdint> 


class RNGSource 
{ 
    public: 
     virtual ~RNGSource() = default; 
     typedef uint_fast32_t result_type; 
     virtual result_type operator()() = 0; 
     virtual result_type min() const = 0; 
     virtual result_type max() const = 0; 
}; 


template <class Generator> 
class RNGSourceWrap : public RNGSource 
{ 
    public: 
     RNGSourceWrap(Generator* rng); 

     virtual result_type operator()() override; 
     virtual result_type min() const override; 
     virtual result_type max() const override; 
     Generator* rng() const; 

    private: 
     Generator* rngVal; 
}; 

template <class Generator> 
RNGSourceWrap<Generator>::RNGSourceWrap(Generator* rng) 
    : rngVal(rng) { } 

template <class Generator> 
typename RNGSourceWrap<Generator>::result_type 
RNGSourceWrap<Generator>::operator()() { return rngVal->operator()(); } 

template <class Generator> 
typename RNGSourceWrap<Generator>::result_type 
RNGSourceWrap<Generator>::min() const { return rngVal->min(); } 

template <class Generator> 
typename RNGSourceWrap<Generator>::result_type 
RNGSourceWrap<Generator>::max() const { return rngVal->max(); } 

template <class Generator> 
Generator* RNGSourceWrap<Generator>::rng() const { return rngVal; } 
#endif // RANDOM_H 

我寫了一個小主測試funtionality：

#include "random.h" 
#include <random> 
#include <iostream> 

int main() 
{ 
    std::mt19937 rng; 

    RNGSource* rngWrap = new RNGSourceWrap<std::mt19937>(&rng); 
    std::uniform_int_distribution<int> distro(1, 6); 
    int myInt = distro(*rngWrap); 

    std::cout << myInt << std::endl; 

    delete rngWrap; 

    return 0; 
} 

此代碼編譯，並且當使用Linux克++編譯並使用MinGW的C++ 14標準沒有警告或錯誤運行。然而，當MSVC編譯它生成錯誤（使用Visual Studio 2017年社區）：

1>------ Build started: Project: RNGTestApp, Configuration: Debug Win32 ------ 
1>main.cpp 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\xutility(3479): error C2352: 'RNGSource::max': illegal call of non-static member function 
1>[PATH REMOVED]\visual studio 2017\projects\rngtestapp\random.h(14): note: see declaration of 'RNGSource::max' 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\xutility(3476): note: while compiling class template member function 'std::_Rng_from_urng<unsigned int,_Engine>::_Rng_from_urng(_Urng &)' 
1>  with 
1>  [ 
1>   _Engine=RNGSource, 
1>   _Urng=RNGSource 
1>  ] 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\random(2353): note: see reference to function template instantiation 'std::_Rng_from_urng<unsigned int,_Engine>::_Rng_from_urng(_Urng &)' being compiled 
1>  with 
1>  [ 
1>   _Engine=RNGSource, 
1>   _Urng=RNGSource 
1>  ] 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\random(2353): note: see reference to class template instantiation 'std::_Rng_from_urng<unsigned int,_Engine>' being compiled 
1>  with 
1>  [ 
1>   _Engine=RNGSource 
1>  ] 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\random(2312): note: see reference to function template instantiation 'int std::uniform_int<_Ty>::_Eval<_Engine>(_Engine &,_Ty,_Ty) const' being compiled 
1>  with 
1>  [ 
1>   _Ty=int, 
1>   _Engine=RNGSource 
1>  ] 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\random(2312): note: see reference to function template instantiation 'int std::uniform_int<_Ty>::_Eval<_Engine>(_Engine &,_Ty,_Ty) const' being compiled 
1>  with 
1>  [ 
1>   _Ty=int, 
1>   _Engine=RNGSource 
1>  ] 
1>[PATH REMOVED]\visual studio 2017\projects\rngtestapp\main.cpp(11): note: see reference to function template instantiation 'int std::uniform_int<_Ty>::operator()<RNGSource>(_Engine &) const' being compiled 
1>  with 
1>  [ 
1>   _Ty=int, 
1>   _Engine=RNGSource 
1>  ] 
1>[PATH REMOVED]\visual studio 2017\projects\rngtestapp\main.cpp(11): note: see reference to function template instantiation 'int std::uniform_int<_Ty>::operator()<RNGSource>(_Engine &) const' being compiled 
1>  with 
1>  [ 
1>   _Ty=int, 
1>   _Engine=RNGSource 
1>  ] 
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\include\xutility(3479): error C2352: 'RNGSource::min': illegal call of non-static member function 
1>[PATH REMOVED]\visual studio 2017\projects\rngtestapp\random.h(13): note: see declaration of 'RNGSource::min' 
1>Done building project "RNGTestApp.vcxproj" -- FAILED. 

鑑於這並編譯使用Linux的G ++和MinGW，並似乎有資格作爲實施UniformRandomBitGenerator標準，這是一個編譯器錯誤？

Answer 1

在我看來，你理解UniformRandomBitGenerator概念錯誤的措辭。 result_type，max和min都被定義static，你的執行沒有這樣做。雖然在表述中沒有使用「靜態」一詞，但仔細看看錶達式是如何寫入的。

在你封裝器，您可以相應地包裝：

template <class Generator> 
typename RNGSourceWrap<Generator>::result_type 
RNGSourceWrap<Generator>::min() const { return Generator::min(); } 

...並宣佈各自的方法是靜態的。但是，如果有人打電話RNGSource::min()這將是無效的。