从映射<字符串、矢量中对唯一值进行排序<string>>

Question

我的头文件中有一个自定义映射

class Tramway
{
private:
using stations = std::vector <std::string>;
using Tramlines = std::map <std::string, stations>;
...../

我正在尝试对唯一值进行排序，但到目前为止，我的方法是产生编译错误。这是我的密码。

void Tramway::print_stations(const Tramway::Tramlines &tramlines)
{
for(auto map_iter = tramlines.cbegin(); map_iter != tramlines.cend(); ++map_iter)
{
std::unique(map_iter->second.cbegin(), map_iter->second.cend());
std::sort(map_iter->second.begin(), map_iter->second.end());
for( auto vec_iter = map_iter->second.cbegin() ; vec_iter != map_iter->second.cend() ; ++vec_iter )
std::cout << *vec_iter << std::endl;
}
}

有没有一种方法可以获得唯一的值并同时对其进行排序？我尝试了std::sort(std::unique(..,..))，但std::sort()需要两个参数才能工作。

以下是我不断获得的错误

x86_64-w64-mingw327.3.0includec++bitsstl_algobase.h:148: error: no matching function for call to 'swap(const std::__cxx11::basic_string<char>&, const std::__cxx11::basic_string<char>&)'
swap(*__a, *__b);
~~~~^~~~~~~~~~~~
x86_64-w64-mingw327.3.0includec++bitsstl_algo.h:975: error: passing 'const std::__cxx11::basic_string<char>' as 'this' argument discards qualifiers [-fpermissive]
*++__dest = _GLIBCXX_MOVE(*__first);
^
x86_64-w64-mingw327.3.0includec++bitsstl_algo.h:1852: error: passing 'const std::__cxx11::basic_string<char>' as 'this' argument discards qualifiers [-fpermissive]
*__first = _GLIBCXX_MOVE(__val);
^
x86_64-w64-mingw327.3.0includec++bitsstl_heap.h:252: error: passing 'const std::__cxx11::basic_string<char>' as 'this' argument discards qualifiers [-fpermissive]
*__result = _GLIBCXX_MOVE(*__first);
^
x86_64-w64-mingw327.3.0includec++bitsmove.h:187: error: no type named 'type' in 'struct std::enable_if<false, void>'
86_64-w64-mingw327.3.0includec++bitsstl_heap.h:225: error: passing 'const std::__cxx11::basic_string<char>' as 'this' argument discards qualifiers [-fpermissive]
*(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first + __secondChild));
^
86_64-w64-mingw327.3.0includec++bitsstl_heap.h:231: error: passing 'const std::__cxx11::basic_string<char>' as 'this' argument discards qualifiers [-fpermissive]
*(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first
^
x86_64-w64-mingw327.3.0includec++bitsstl_algobase.h:548: error: passing 'const std::__cxx11::basic_string<char>' as 'this' argument discards qualifiers [-fpermissive]
*--__result = std::move(*--__last);
~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

Answer 1

三个问题：

1. std::unique需要可修改的迭代器。您不应该将cbegin/cend传递给他们。该函数还应采用可修改的引用。

2. 先std::sort，后std::unique。CCD_ 7仅去除相邻的等效元素。

3. std::unique没有更改矢量大小的权限。它只是将结果序列放在向量的开头。使用删除-擦除习惯用法来删除已删除的元素。

固定代码：

void Tramway::print_stations(Tramway::Tramlines& tramlines)
{
for (auto map_iter = tramlines.cbegin(); map_iter != tramlines.cend(); ++map_iter)
{
std::sort(map_iter->second.begin(), map_iter->second.end());
map_iter->second.erase(std::unique(map_iter->second.begin(), map_iter->second.end()), map_iter->second.end());
for (auto vec_iter = map_iter->second.cbegin(); vec_iter != map_iter->second.cend(); ++vec_iter)
std::cout << *vec_iter << 'n';
}    
}

此外，考虑使用基于范围的循环和参考来简化代码：

void Tramway::print_stations(Tramway::Tramlines& tramlines)
{
for (auto& tramline : tramlines) {
auto& station = tramline.second;
std::sort(station.begin(), station.end());
station.erase(std::unique(station.begin(), station.end()), station.end());
std::copy(station.begin(), station.end(),
std::ostream_iterator<stations>{std::cout, 'n'});
}    
}