使用unique_ptr的字符的C++数组

Question

首先，我知道这不是最好的方法，我只是想看看应该怎么做。我创建了一个名为bord的类，它包含一个成员

        std::unique_ptr<std::unique_ptr<char>[] > char_bord;

这应该是正确的语法，然后我尝试在构造函数中初始化它：

bord::bord():char_bord(new std::unique_ptr<char>[10])
{
    //char_bord=new std::unique_ptr<char>[10]; //This did not seem to work aswell.
    for(int i=0;i<10;i++)
      char_bord[i]=new std::unique_ptr<char>[](new char[10]); 
    return;
}

这导致了下面的一堆错误，我没能破译这些错误。

jelmer@jelmer-N56JN:~/Git/Board/lib$ g++ -std=c++0x bord.c
In file included from bord.c:1:0:
bord.h:20:1: error: new types may not be defined in a return type
 class bord
 ^
bord.h:20:1: note: (perhaps a semicolon is missing after the definition of ‘bord’)
bord.c:3:12: error: return type specification for constructor invalid
 bord::bord():char_bord(new std::unique_ptr<char>[10])
            ^
bord.c: In constructor ‘bord::bord()’:
bord.c:7:46: error: expected primary-expression before ‘]’ token
       char_bord[i]=new std::unique_ptr<char>[](new char[10]); 
                                              ^
bord.c:7:60: error: parenthesized initializer in array new [-fpermissive]
       char_bord[i]=new std::unique_ptr<char>[](new char[10]); 
                                                            ^
bord.c:7:19: error: no match for ‘operator=’ (operand types are ‘std::unique_ptr<char>’ and ‘std::unique_ptr<char>*’)
       char_bord[i]=new std::unique_ptr<char>[](new char[10]); 
                   ^
bord.c:7:19: note: candidates are:
In file included from /usr/include/c++/4.9/memory:81:0,
                 from bord.h:19,
                 from bord.c:1:
/usr/include/c++/4.9/bits/unique_ptr.h:249:7: note: std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Tp, _Dp>&&) [with _Tp = char; _Dp = std::default_delete<char>]
       operator=(unique_ptr&& __u) noexcept
       ^
/usr/include/c++/4.9/bits/unique_ptr.h:249:7: note:   no known conversion for argument 1 from ‘std::unique_ptr<char>*’ to ‘std::unique_ptr<char>&&’
/usr/include/c++/4.9/bits/unique_ptr.h:269:2: note: template<class _Up, class _Ep> typename std::enable_if<std::__and_<std::is_convertible<typename std::unique_ptr<_Up, _Ep>::pointer, typename std::unique_ptr<_Tp, _Dp>::_Pointer::type>, std::__not_<std::is_array<_Up> > >::value, std::unique_ptr<_Tp, _Dp>&>::type std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Up, _Ep>&&) [with _Up = _Up; _Ep = _Ep; _Tp = char; _Dp = std::default_delete<char>]
  operator=(unique_ptr<_Up, _Ep>&& __u) noexcept
  ^
/usr/include/c++/4.9/bits/unique_ptr.h:269:2: note:   template argument deduction/substitution failed:
bord.c:7:19: note:   mismatched types ‘std::unique_ptr<_Tp, _Dp>’ and ‘std::unique_ptr<char>*’
       char_bord[i]=new std::unique_ptr<char>[](new char[10]); 
                   ^
In file included from /usr/include/c++/4.9/memory:81:0,
                 from bord.h:19,
                 from bord.c:1:
/usr/include/c++/4.9/bits/unique_ptr.h:278:7: note: std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::nullptr_t) [with _Tp = char; _Dp = std::default_delete<char>; std::nullptr_t = std::nullptr_t]
       operator=(nullptr_t) noexcept
       ^
/usr/include/c++/4.9/bits/unique_ptr.h:278:7: note:   no known conversion for argument 1 from ‘std::unique_ptr<char>*’ to ‘std::nullptr_t’

我做错了什么，假设我做错了。

Answer 1

以下是一些代码，演示了我认为您想要的东西：

#include <iostream>
#include <algorithm>
#include <iterator>
#include <memory>
using namespace std;
using array_ptr_type = std::unique_ptr<char[]>;
using array_of_arrays_type = std::unique_ptr<array_ptr_type[]>;
auto main() -> int
{
    auto x = array_ptr_type(new char[10]);
    auto y = array_ptr_type(new char[10]);
    for (int i = 0 ; i < 10 ; ++i)
    {
        x[i] = char('0' + i);
        y[i] = char('0' + 9 - i);
    }
    auto pxy = array_of_arrays_type(new array_ptr_type[2]);
    pxy[0] = move(x);
    pxy[1] = move(y);
    for (int i = 0 ; i < 2 ; ++i) {
        copy(&pxy[i][0], &pxy[i][10], ostream_iterator<char>(cout, ", "));
        cout << endl;
    }
    return 0;
}

预期输出：

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 
9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 

当然，正如您所知，不建议使用这些方法——vector<vector<char>>会更干净、更易于维护。

Answer 2

您必须使用专业化：

std::unique_ptr<char[]> chars(new char[1024]);

这是因为std::unique_ptr不像std::shared_ptr那样支持自定义deleter（在这种写作风格中）。

std::unique_ptr使用std::default_delete作为删除器。很快，如果您将参数类型指定为class T，它将使用默认的delete，但如果您编写class T[]（在此专门化中），std::unique_ptr将使用delete[]。

但是最好使用一些容器，而不是c样式的数组。