Question

我正在尝试移植一些Visual C ++（VS2005）代码，以便它可以在VS2005和C ++ Builder XE下编译。下面的代码在VS2005下编译得很好但在C ++ Builder XE下，我得到以下错误：

[BCC32错误] time_stamp.h（49）：E2327运算符可能没有默认参数值

以下是有问题的代码：（time_stamp.h）

template<typename counter_type>
class time_stamp
{
typedef time_span<counter_type>                     time_span_type;
typedef typename counter_type::value_type   value_type;

public:

/* some code removed for sake of this post, next line is the one causing the error */

friend time_span<counter_type> operator-(const time_stamp<counter_type> &first, const time_stamp<counter_type> &second)
{
  return time_span<counter_type>(first.m_stamp - second.m_stamp);
}

private:

value_type m_stamp;

}

time_span模板如下（time_span.h）：

template<typename counter_type>
class time_span
{
public:
// TYPES
  typedef counter_type          counter_type;
  typedef typename counter_type::value_type value_type;

/* rest removed for sake of this post */
}

C ++ Builder编译器似乎不喜欢该行：朋友time_span operator-（const time_stamp＆amp; first，const time_stamp＆amp; second）

我是模板的新手，这种语法让我失望，或者至少是我无法理解的编译器错误。对我来说，尽管编译器这么说，但似乎没有默认的参数值。我正在将错误消息解释为const time_stamp＆amp;当它看起来像是传递类型为time_stamp的引用时是一个默认值。

感谢阅读＆amp;回复。非常感谢帮助理解和修复。

---编辑：

如果我重新构建上面的调用，如下所示：

friend time_span<counter_type> operator-( (const time_stamp<counter_type>& first, const time_stamp<counter_type>& second) );

在类定义之外，我描述了函数：

template<typename counter_type>
time_span<counter_type> operator-( (const time_stamp<counter_type>& first, const time_stamp<counter_type>& second) )
{
return time_span<counter_type>(first.m_stamp-second.m_stamp);
}

然后我收到此错误：

[BCC32错误] time_stamp.hpp（56）：E2082' - （int（*）（const time_stamp＆amp;，const time_stamp＆amp;））'必须是成员函数或具有类类型的参数

Answer 1

[替换我以前的答案！]

这可能与http://www.parashift.com/c++-faq/templates.html#faq-35.16有关。

由于您要定义的函数实际上是一个模板函数（它取决于counter_type），您应该在friend声明之前声明它，然后声明一个函数模板实例化为friend：

// time_stamp.h
#include "time_span.h"
template<typename counter_type> class time_stamp;
template<typename counter_type> time_span<counter_type> operator-(
    const time_stamp<counter_type>&, const time_stamp<counter_type>& );

template<typename counter_type>
class time_stamp
{
  //...
    friend time_span<counter_type> operator- <> (
        const time_stamp<counter_type>&, const time_stamp<counter_type>&);
};

template<typename counter_type>
inline time_span<counter_type> operator-(
    const time_stamp<counter_type>& first, const time_stamp<counter_type>& second)
{
    return time_span<counter_type>(first.m_stamp - second.m_stamp);
}

Answer 2

尝试：

template<class counter_type>
class .... {
    friend time_span<counter_type> operator-(const time_stamp<counter_type> &first, const time_stamp<counter_type> &second);
};


template<class counter_type>
time_span<counter_type> operator-(const time_stamp<counter_type> &first,
                                  const time_stamp<counter_type> &second)
{
  return time_span<counter_type>(first.m_stamp - second.m_stamp);
}

模板类操作符重载问题

2 个答案: