这段代码不能在我的计算机上编译（用最小的示例编辑）:
// Example program
#include <iostream>
#include <string>
#include <vector>
#include <tuple>
template<class PValues>
inline bool equal(PValues it,
PValues last,
size_t cols,
size_t rows,
size_t offset)
{
if(std::distance(it,last)<offset)
return false;
for(size_t c=0; c<cols; ++c)
{
auto p = it + c*rows;
if(*p != *(p + offset))
return false;
}
return true;
};
int main()
{
std::vector<std::string> vec = {"1","1","1","2","2","2","3","8","8",
"5","5","2","5","5","5","6","8","8",
"3","3","3","4","4","3","9","8","8"};
std::vector<double> nbs = {1,2,3,4,5,6,7,8,9};
auto res = equal(vec.data(), vec.data()+9, 3, 9, 1);
}
我有以下错误:
In file included from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from main.cpp:2:
/usr/include/c++/9/bits/stl_algobase.h: In instantiation of ‘bool std::__equal4(_II1, _II1, _II2, _II2, _BinaryPredicate) [with _II1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _II2 = long unsigned int; _BinaryPredicate = int]’:
/usr/include/c++/9/bits/stl_algobase.h:1219:38: required from ‘bool std::equal(_IIter1, _IIter1, _IIter2, _IIter2, _BinaryPredicate) [with _IIter1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _IIter2 = long unsigned int; _BinaryPredicate = int]’
main.cpp:60:15: required from ‘size_t remove_duplicates_rows_impl(PValues, PResults, size_t, size_t) [with PValues = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; PResults = __gnu_cxx::__normal_iterator<double*, std::vector<double> >; size_t = long unsigned int]’
main.cpp:99:32: required from here
/usr/include/c++/9/bits/stl_algobase.h:1139:13: error: no type named ‘iterator_category’ in ‘struct std::iterator_traits<long unsigned int>’
1139 | using _Cat2 = typename iterator_traits<_II2>::iterator_category;
| ^~~~~
/usr/include/c++/9/bits/stl_algobase.h:1140:13: error: no type named ‘iterator_category’ in ‘struct std::iterator_traits<long unsigned int>’
1140 | using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
| ^~~~~~~~
/usr/include/c++/9/bits/stl_algobase.h:1144:29: error: no matching function for call to ‘distance(long unsigned int&, long unsigned int&)’
1144 | auto __d2 = std::distance(__first2, __last2);
| ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/9/bits/stl_algobase.h:66,
from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from main.cpp:2:
/usr/include/c++/9/bits/stl_iterator_base_funcs.h:138:5: note: candidate: ‘template<class _InputIterator> constexpr typename std::iterator_traits<_Iterator>::difference_type std::distance(_InputIterator, _InputIterator)’
138 | distance(_InputIterator __first, _InputIterator __last)
| ^~~~~~~~
/usr/include/c++/9/bits/stl_iterator_base_funcs.h:138:5: note: template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_iterator_base_funcs.h: In substitution of ‘template<class _InputIterator> constexpr typename std::iterator_traits<_Iterator>::difference_type std::distance(_InputIterator, _InputIterator) [with _InputIterator = long unsigned int]’:
/usr/include/c++/9/bits/stl_algobase.h:1144:29: required from ‘bool std::__equal4(_II1, _II1, _II2, _II2, _BinaryPredicate) [with _II1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _II2 = long unsigned int; _BinaryPredicate = int]’
/usr/include/c++/9/bits/stl_algobase.h:1219:38: required from ‘bool std::equal(_IIter1, _IIter1, _IIter2, _IIter2, _BinaryPredicate) [with _IIter1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _IIter2 = long unsigned int; _BinaryPredicate = int]’
main.cpp:60:15: required from ‘size_t remove_duplicates_rows_impl(PValues, PResults, size_t, size_t) [with PValues = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; PResults = __gnu_cxx::__normal_iterator<double*, std::vector<double> >; size_t = long unsigned int]’
main.cpp:99:32: required from here
/usr/include/c++/9/bits/stl_iterator_base_funcs.h:138:5: error: no type named ‘difference_type’ in ‘struct std::iterator_traits<long unsigned int>’
In file included from /usr/include/c++/9/bits/char_traits.h:39,
from /usr/include/c++/9/ios:40,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from main.cpp:2:
/usr/include/c++/9/bits/stl_algobase.h: In instantiation of ‘bool std::__equal4(_II1, _II1, _II2, _II2, _BinaryPredicate) [with _II1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _II2 = long unsigned int; _BinaryPredicate = int]’:
/usr/include/c++/9/bits/stl_algobase.h:1219:38: required from ‘bool std::equal(_IIter1, _IIter1, _IIter2, _IIter2, _BinaryPredicate) [with _IIter1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _IIter2 = long unsigned int; _BinaryPredicate = int]’
main.cpp:60:15: required from ‘size_t remove_duplicates_rows_impl(PValues, PResults, size_t, size_t) [with PValues = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; PResults = __gnu_cxx::__normal_iterator<double*, std::vector<double> >; size_t = long unsigned int]’
main.cpp:99:32: required from here
/usr/include/c++/9/bits/stl_algobase.h:1153:37: error: invalid type argument of unary ‘*’ (have ‘long unsigned int’)
1153 | if (!bool(__binary_pred(*__first1, *__first2)))
| ^~~~~~~~~
/usr/include/c++/9/bits/stl_algobase.h:1153:25: error: ‘__binary_pred’ cannot be used as a function
1153 | if (!bool(__binary_pred(*__first1, *__first2)))
我觉得奇怪的是:如果我把函数的名称等于equalx（或者equalz，只是一个例子），它会编译。 代码不在godbolt to上编译，但在onlinegdb上编译:https://onlinegdb.com/rym5lk4jp。
我的G++版本:
g++（Ubuntu 9.3.0-10Ubuntu2)9.3.0
用于编译示例的行:
g++-std=C++17-O main main.cpp
如果将对equal的调用从equal(first_v，last_v，cols，rows，1)更改为equal(first_v，last_v，cols，rows，size_t(1)，则代码将编译。
如果更改名称，则代码会编译的原因是有一个名为std::equal的标准算法。 在重载解析中查看此函数，因为前两个参数与函数共享std命名空间，因此会发生依赖于参数的查找。std::equal可能需要5个参数，所有这些参数都是模板化的，因此在重载解析中将被选为最佳匹配。 要使用您的函数，必须进行从int到size_t的隐式转换。
通过将最后一个参数更改为size_t(1)，就不需要进行转换来调用您的函数，因此这就是在重载解决方案中选择的内容。
