如何在模板类上实现操作符重载？
如何在模板类上实现操作符重载？
提问于 2019-11-10 07:02:34
我在尝试重载复数模板类上的加法运算符时遇到了一个问题。
在我的.h中，我对类和运算符函数函数都进行了正向声明，并且我特别重载了operator+<T>，而不仅仅是operator+，这样它就可以处理多种类型。当我只包含.h文件时，它编译得很好，但只要我试图声明MyComplex<int>，它就会给出一些奇怪的错误，我很难破译这些错误。
my_complex.h：
#ifndef _MY_COMPLEX_H
#define _MY_COMPLEX_H
using namespace std;
//forward declarations
template<typename T> class MyComplex;
template<typename T> MyComplex<T> operator+(const MyComplex<T>& cmplx1, const MyComplex<T>& cmplx2);
template<typename T>
class MyComplex{
private:
T _real;
T _imaginary;
public:
MyComplex();
MyComplex(T real, T img);
T getReal();
T getImaginary();
void setReal(T real);
void setImaginary(T img);
friend MyComplex operator+<T>(const MyComplex& cmplx1, const MyComplex& cmplx2);
}
#endifmy_complex.cpp：
#include "my_complex.h"
...
template <typename T>
MyComplex<T> operator+(const MyComplex<T>& cmplx1, const MyComplex<T>& cmplx2){
MyComplex<T> temp;
temp._real = cmplx1._real + cmplx2._real;
temp._imaginary = cmplx1._imaginary + cmplx2._imaginary;
return temp;
}
...main.cpp：
#include "my_complex.h"
int main(int argc, char* argv[]){
MyComplex<int> cmplx1 = MyComplex<int>(3, 5);//error is here
MyComplex<int> cmplx2 = MyComplex<int>(5, 7);
cmplx1 = cmplx1 + cmplx2;
return 0;
}当我只在主文件中包含.h文件时，它编译得很好，但只要我试图声明MyComplex<int>，它就会给出一些我很难破译的错误。
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
from /usr/include/c++/7/bits/char_traits.h:39,
from /usr/include/c++/7/ios:40,
from /usr/include/c++/7/ostream:38,
from /usr/include/c++/7/iostream:39,
from main.cpp:1:
/usr/include/c++/7/bits/stl_iterator.h: In instantiation of ‘class std::reverse_iterator<int>’:
/usr/include/c++/7/bits/stl_iterator.h:400:5: required by substitution of ‘template<class _Iterator> std::reverse_iterator<_Iterator> std::operator+(typename std::reverse_iterator<_Iterator>::difference_type, const std::reverse_iterator<_Iterator>&) [with _Iterator = int]’
my_complex.h:36:20: required from ‘class MyComplex<int>’
main.cpp:8:17: required from here
/usr/include/c++/7/bits/stl_iterator.h:101:11: error: no type named ‘iterator_category’ in ‘struct std::iterator_traits<int>’
class reverse_iterator
^~~~~~~~~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:115:55: error: no type named ‘difference_type’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::difference_type difference_type;
^~~~~~~~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:116:48: error: no type named ‘pointer’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::pointer pointer;
^~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:117:50: error: no type named ‘reference’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::reference reference;
^~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h: In instantiation of ‘class std::move_iterator<int>’:
/usr/include/c++/7/bits/stl_iterator.h:1201:5: required by substitution of ‘template<class _Iterator> std::move_iterator<_IteratorL> std::operator+(typename std::move_iterator<_IteratorL>::difference_type, const std::move_iterator<_IteratorL>&) [with _Iterator = int]’
my_complex.h:36:20: required from ‘class MyComplex<int>’
main.cpp:8:17: required from here
/usr/include/c++/7/bits/stl_iterator.h:1019:50: error: no type named ‘reference’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::reference __base_ref;
^~~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:1023:57: error: no type named ‘iterator_category’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::iterator_category iterator_category;
^~~~~~~~~~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:1024:52: error: no type named ‘value_type’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::value_type value_type;
^~~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:1025:55: error: no type named ‘difference_type’ in ‘struct std::iterator_traits<int>’
typedef typename __traits_type::difference_type difference_type;
^~~~~~~~~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:1032:24: error: no type named ‘reference’ in ‘struct std::iterator_traits<int>’
__base_ref>::type reference;
^~~~~~~~~回答 1
Stack Overflow用户
回答已采纳
发布于 2019-11-10 07:05:45
你不能在一个.cpp文件中定义一个模板化的方法，把它放在头文件中，它应该可以工作。请参阅https://isocpp.org/wiki/faq/templates#templates-defn-vs-decl
此外，这
friend MyComplex operator+<T>(const MyComplex& cmplx1, const MyComplex& cmplx2);
// should match the forward declaration
friend MyComplex<T> operator+<>(const MyComplex<T>& cmplx1, const MyComplex<T>& cmplx2);因此您应该添加<T>
这实际上不能解释你的错误，但是错误消息不适合你给出的文件，.hpp没有36行，但这就是错误所在，所以调试相当困难。
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原文链接：
https://stackoverflow.com/questions/58784315
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