模糊的C ++编译错误 [英] Nebulous C++ Compile Error

问题描述

任何人都可以对此提出建议

Can anyone advise on this:

In file included from recorders/r5000channel.h:13:0,
             from recorders/r5000channel.cpp:11:
recorders/dtvchannel.h:53:18: warning: ‘virtual bool DTVChannel::Tune(const IPTVTuningData&)’ was hidden [-Woverloaded-virtual]
 virtual bool Tune(const IPTVTuningData&) { return false; }
              ^
In file included from recorders/r5000channel.cpp:11:0:
recorders/r5000channel.h:29:18: warning:   by ‘virtual bool R5000Channel::Tune(const DTVMultiplex&, QString)’ [-Woverloaded-virtual]
 virtual bool Tune(const DTVMultiplex &/*tuning*/, QString /*inputname*/)
              ^
In file included from recorders/r5000channel.h:13:0,
             from recorders/r5000channel.cpp:11:
recorders/dtvchannel.h:65:18: warning: ‘virtual bool DTVChannel::Tune(const QString&, int)’ was hidden [-Woverloaded-virtual]
 virtual bool Tune(const QString &freqid, int finetune)
              ^
In file included from recorders/r5000channel.cpp:11:0:
recorders/r5000channel.h:29:18: warning:   by ‘virtual bool R5000Channel::Tune(const DTVMultiplex&, QString)’ [-Woverloaded-virtual]
 virtual bool Tune(const DTVMultiplex &/*tuning*/, QString /*inputname*/)
              ^
In file included from recorders/r5000channel.h:13:0,
             from recorders/r5000channel.cpp:11:
recorders/dtvchannel.h:71:18: warning: ‘virtual bool DTVChannel::Tune(uint64_t, QString)’ was hidden [-Woverloaded-virtual]
 virtual bool Tune(uint64_t frequency, QString inputname)
              ^
In file included from recorders/r5000channel.cpp:11:0:
recorders/r5000channel.h:29:18: warning:   by ‘virtual bool R5000Channel::Tune(const DTVMultiplex&, QString)’ [-Woverloaded-virtual]
 virtual bool Tune(const DTVMultiplex &/*tuning*/, QString /*inputname*/)

r5000channel.h- https://pastee.org/rjajf

r5000channel.h - https://pastee.org/rjajf

r5000channel.cpp- https://pastee.org/qangy

r5000channel.cpp - https://pastee.org/qangy

推荐答案

请注意，这不是错误，而是警告.看来您的基类包含名为 Tune 的 virtual 函数的重载版本:当您覆盖其中的一个时，使用派生对象时，基类中的所有版本都会被隐藏.通常，这是无意的，处理重载的 virtual 函数的正常方法是使 virtual 函数得到 protected ，从 public 转发(可能还有 inline )功能.参见例如 std :: num_get< ...> 中的 virtual 函数.

Note that it isn't an error but a warning. It seems your base classes contain overloaded version of the virtual function named Tune: when you override one of them, all versions in bases are hidden when using a derived object. Normally, this is unintentional and the normal approach to deal with overloaded virtual functions is to make the virtual functions protected, delegating to them from a public forwarding (and probably inline) function. See, e.g., the virtual functions in std::num_get<...>.

另一种避免隐藏的方法是提供 using 声明以及 virtual 函数的替代.就个人而言，我更喜欢转发方法.

Another approach to avoid the hiding is to provide using-declarations together with the overrides of virtual functions. Personally, I prefer the forwarding approach.

显示的警告实际上来自头文件.这意味着您使用的库是草率的，或者您创建的草率基类有些草率.

The warnings shown are actually from header files. This means that either the library you are using is sloppy or you created a somewhat sloppy base class.

这是 SSCCE ，其中显示了问题，并在注释中给出了解决方法:

Here is an SSCCE showing the problem and, in a comment, the fix:

struct base
{
    virtual void foo(int) {}
    virtual void foo(bool) {}
};

struct derived: base
{
    virtual void foo(int) {}
    // add this: using base::foo;
};

int main()
{
}

使用上述代码编译上面的代码时，会收到以下消息(缩写为仅显示编译器版本和警告):

When compiling the above code with I get these messages (abbreviated to only show the compiler version and the warnings):

$ g++ -v -c -Woverloaded-virtual overloaded-virtual.cpp
[...]
GNU C++ (GCC) version 4.9.0 20131031 (experimental) (x86_64-apple-darwin13.0.0)
    compiled by GNU C version 4.9.0 20131102 (experimental), GMP version 5.0.5, MPFR version 3.1.1, MPC version 1.0.1
[...]
overloaded-virtual.cpp:4:22: warning: ‘virtual void base::foo(bool)’ was hidden [-Woverloaded-virtual]
         virtual void foo(bool) {}
                      ^
overloaded-virtual.cpp:9:22: warning:   by ‘virtual void derived::foo(int)’ [-Woverloaded-virtual]
         virtual void foo(int) {}
                      ^

添加评论时，警告消失(如预期).

When adding the comment, the warnings go away (as expected).

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