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[英]How do I use boost::adaptors::transformed to produce a range from a templated class and a vector?
[英]How do I boost::range::sort() a boost::transformed_range?
我想從基於foo
成員的vector<foo>
獲得唯一元素。 我正在使用boost::adaptors::transform
選擇成員,然后進行排序,然后使用boost::adaptors::unique
。 我無法使排序步驟正常工作。 暫時不考慮unique
調用,我已經在Coliru上嘗試了以下代碼。
#include <iostream>
#include <string>
#include <vector>
#include <boost/range/adaptor/transformed.hpp>
#include <boost/range/algorithm/sort.hpp>
struct foo
{
foo(std::string a) : bar(a) {}
std::string bar;
bool operator<(const foo& rhs) const {return bar < rhs.bar;}
};
int main()
{
std::vector<foo> words = { foo("z"), foo("d"), foo("b"), foo("c") };
#if 1
{
auto asString = boost::adaptors::transform(words, +[](const foo& x) {return x.bar;});
auto sortedStrings = boost::range::sort(asString);
for (const auto& el : sortedStrings)
std::cout << el << std::endl;
}
#else
{
auto asString = boost::adaptors::transform(words, +[](const foo& x) {return x.bar;});
std::sort(asString.begin().base(), asString.end().base());
for (const auto& el : asString)
std::cout << el << std::endl;
}
{
auto sortedStrings = boost::range::sort(words);
for (const auto& el : sortedStrings)
std::cout << el.bar << std::endl;
}
#endif
return 0;
}
#if
部分無效:
In file included from /usr/local/include/c++/6.3.0/bits/char_traits.h:39:0,
from /usr/local/include/c++/6.3.0/ios:40,
from /usr/local/include/c++/6.3.0/ostream:38,
from /usr/local/include/c++/6.3.0/iostream:39,
from main.cpp:1:
/usr/local/include/c++/6.3.0/bits/stl_algobase.h: In instantiation of 'void std::iter_swap(_ForwardIterator1, _ForwardIterator2) [with _ForwardIterator1 = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>; _ForwardIterator2 = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>]':
/usr/local/include/c++/6.3.0/bits/stl_algo.h:84:20: required from 'void std::__move_median_to_first(_Iterator, _Iterator, _Iterator, _Iterator, _Compare) [with _Iterator = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
/usr/local/include/c++/6.3.0/bits/stl_algo.h:1918:34: required from '_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
/usr/local/include/c++/6.3.0/bits/stl_algo.h:1950:38: required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>; _Size = long int; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
/usr/local/include/c++/6.3.0/bits/stl_algo.h:1965:25: required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
/usr/local/include/c++/6.3.0/bits/stl_algo.h:4707:18: required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>]'
/usr/local/include/boost/range/algorithm/sort.hpp:33:14: required from 'RandomAccessRange& boost::range::sort(RandomAccessRange&) [with RandomAccessRange = boost::range_detail::transformed_range<std::__cxx11::basic_string<char> (*)(const foo&), std::vector<foo> >]'
main.cpp:27:57: required from here
/usr/local/include/c++/6.3.0/bits/stl_algobase.h:148:11: error: no matching function for call to 'swap(boost::iterators::detail::iterator_facade_base<boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>, std::__cxx11::basic_string<char>, boost::iterators::random_access_traversal_tag, std::__cxx11::basic_string<char>, long int, false, false>::reference, boost::iterators::detail::iterator_facade_base<boost::iterators::transform_iterator<std::__cxx11::basic_string<char> (*)(const foo&), __gnu_cxx::__normal_iterator<foo*, std::vector<foo> >, boost::iterators::use_default, boost::iterators::use_default>, std::__cxx11::basic_string<char>, boost::iterators::random_access_traversal_tag, std::__cxx11::basic_string<char>, long int, false, false>::reference)'
swap(*__a, *__b);
而#else
部分中具有基本迭代器類型的std::sort
可以工作。 我不明白為什么。 在我的實際用例中,我還使用了boost::adaptors::indirect
和boost::adaptors::filter
(而且我更喜歡在進行排序之前進行過濾,或者至少嘗試這樣做,看看如何它執行),所以這就是為什么我在執行轉換之前不簡單地使用lambda謂詞對words
進行排序。
問題是您有一個無法交換的臨時字符串視圖。 您可以使用以下方法修復代碼:
auto asString = boost::adaptors::transform(words, +[](foo& x) -> std::string& {return x.bar;});
請注意,您可以直接對字符串而不是類進行排序。
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