c++ - 在 C++ 中随机排列字符串列表

Question

我尝试打乱以下字符串列表:

list<string> l({"10000007", "1", "4", "5", "7", "12", "23", "25", "26", "27", "30", "31", "32", "44", "46", "47", "59", "65", "91"})

我所有的尝试都失败了。这是我最好的尝试之一。

尝试 1

基本上我从这个回答Randomize a std::list<std::string>复制

#include <iostream>
#include <functional>
#include <iterator>
#include <algorithm>
#include <string>
#include <list>
#include <vector>
#include <random>
#include <numeric>

int main() {
    std::list<std::string> l({"10000007", "1", "4", "5", "7", "12", "23", "25", "26", "27", "30", "31", "32", "44", "46", "47", "59", "65", "91"});
    std::vector<std::reference_wrapper<std::string>> v(l.cbegin(), l.cend());
    std::random_device rd;
    std::mt19937 generator(rd());
    std::shuffle(v.begin(), v.end(), generator);
    std::cout << "Original list:\n";
    std::copy(l.cbegin(), l.cend(), std::ostream_iterator<std::string>(std::cout, " "));
    std::cout << "\nShuffled view:\n";
    std::copy(v.cbegin(), v.cend(), std::ostream_iterator<std::string>(std::cout, " "));
}

我有这个错误跟踪:

In file included from /usr/include/c++/7/vector:62:0,
                 from /usr/include/c++/7/functional:61,
                 from prueba.cpp:2:
/usr/include/c++/7/bits/stl_construct.h: In instantiation of ‘void std::_Construct(_T1*, _Args&& ...) [with _T1 = std::reference_wrapper<std::__cxx11::basic_string<char> >; _Args = {const std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&}]’:
/usr/include/c++/7/bits/stl_uninitialized.h:83:18:   required from ‘static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::_List_const_iterator<std::__cxx11::basic_string<char> >; _ForwardIterator = std::reference_wrapper<std::__cxx11::basic_string<char> >*; bool _TrivialValueTypes = false]’
/usr/include/c++/7/bits/stl_uninitialized.h:134:15:   required from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::_List_const_iterator<std::__cxx11::basic_string<char> >; _ForwardIterator = std::reference_wrapper<std::__cxx11::basic_string<char> >*]’
/usr/include/c++/7/bits/stl_uninitialized.h:289:37:   required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = std::_List_const_iterator<std::__cxx11::basic_string<char> >; _ForwardIterator = std::reference_wrapper<std::__cxx11::basic_string<char> >*; _Tp = std::reference_wrapper<std::__cxx11::basic_string<char> >]’
/usr/include/c++/7/bits/stl_vector.h:1331:33:   required from ‘void std::vector<_Tp, _Alloc>::_M_range_initialize(_ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = std::_List_const_iterator<std::__cxx11::basic_string<char> >; _Tp = std::reference_wrapper<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::reference_wrapper<std::__cxx11::basic_string<char> > >]’
/usr/include/c++/7/bits/stl_vector.h:1299:23:   required from ‘void std::vector<_Tp, _Alloc>::_M_initialize_dispatch(_InputIterator, _InputIterator, std::__false_type) [with _InputIterator = std::_List_const_iterator<std::__cxx11::basic_string<char> >; _Tp = std::reference_wrapper<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::reference_wrapper<std::__cxx11::basic_string<char> > >]’
/usr/include/c++/7/bits/stl_vector.h:414:26:   required from ‘std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const allocator_type&) [with _InputIterator = std::_List_const_iterator<std::__cxx11::basic_string<char> >; <template-parameter-2-2> = void; _Tp = std::reference_wrapper<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::reference_wrapper<std::__cxx11::basic_string<char> > >; std::vector<_Tp, _Alloc>::allocator_type = std::allocator<std::reference_wrapper<std::__cxx11::basic_string<char> > >]’
prueba.cpp:13:76:   required from here
/usr/include/c++/7/bits/stl_construct.h:75:7: error: binding reference of type ‘std::__cxx11::basic_string<char>&’ to ‘const std::__cxx11::basic_string<char>’ discards qualifiers
     { ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/7/bits/std_function.h:44:0,
                 from /usr/include/c++/7/functional:58,
                 from prueba.cpp:2:
/usr/include/c++/7/bits/refwrap.h:334:7: note:   initializing argument 1 of ‘std::reference_wrapper<_Tp>::reference_wrapper(_Tp&) [with _Tp = std::__cxx11::basic_string<char>]’
       reference_wrapper(_Tp& __indata) noexcept
       ^~~~~~~~~~~~~~~~~

我试图理解 reference_wrapper 在这个例子中做了什么，但没有成功。

其他尝试

我对经典组合的所有尝试也都失败了...使用random_engine、shuffle 和srand跟踪数千行错误。

为什么不转换成整数？

在我的原始代码中，有两个 .json 文件，jsons 总是有字符串格式的键。我知道我可以将字符串列表转换为整数列表，但问题是我正在创建算法并且有:

• 2000 个列表
• 算法迭代 2000 次
• 您必须每次迭代多次执行此转换(字符串到 int，int 到字符串...)

所以我认为这个选项在计算上会非常昂贵。

提前致谢。

Answer 1

在这一行:

std::vector<std::reference_wrapper<std::string>> v(l.cbegin(), l.cend());

您正在使用 const_iterator s 构造 vector ，这会在构造 reference_wrapper<std::string> 时导致类型不匹配错误来自 const std::string .

相反，您需要非常量迭代器，如下所示:

std::vector<std::reference_wrapper<std::string>> v(l.begin(), l.end());

这是一个 demo .