Question

我有以下代码片段无法编译......似乎应该这样，但它现在正在躲避我。非常感谢任何帮助/建议！

#include <atomic>
#include <memory>

struct MyClass {

static void free_lock(std::atomic<int>** lck) { (*lck)->store(0); }

typedef std::unique_ptr<std::atomic<int>*, decltype(&MyClass::free_lock)> lock_scope;

static lock_scope get_lock() {
    static std::atomic<int> lck(0);
    int ref = 0;
    return lock_scope(&lck, &MyClass::free_lock);
}

};

Clang 3.2报告了以下错误消息

Compilation finished with errors:
source.cpp:13:23: error: no matching constructor for initialization of 'lock_scope' (aka 'unique_ptr *, decltype(&MyClass::free_lock)>')
        return lock_scope(&lck, &MyClass::free_lock);
                         ^          ~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:130:7: note: candidate constructor not viable: no known conversion from 'std::atomic *' to 'pointer' (aka 'std::atomic **') for 1st argument
      unique_ptr(pointer __p,
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:125:7: note: candidate constructor not viable: no known conversion from 'std::atomic *' to 'pointer' (aka 'std::atomic **') for 1st argument
      unique_ptr(pointer __p,
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:155:2: note: candidate constructor template not viable: requires single argument '__u', but 2 arguments were provided
        unique_ptr(unique_ptr&& __u) noexcept
        ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:164:2: note: candidate constructor template not viable: requires single argument '__u', but 2 arguments were provided
        unique_ptr(auto_ptr&& __u) noexcept
        ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:114:17: note: candidate constructor not viable: requires 0 arguments, but 2 were provided
      constexpr unique_ptr() noexcept
                ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:120:7: note: candidate constructor not viable: requires single argument '__p', but 2 arguments were provided
      unique_ptr(pointer __p) noexcept
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:136:17: note: candidate constructor not viable: requires 1 argument, but 2 were provided
      constexpr unique_ptr(nullptr_t) noexcept
                ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:142:7: note: candidate constructor not viable: requires single argument '__u', but 2 arguments were provided
      unique_ptr(unique_ptr&& __u) noexcept
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:262:7: note: candidate constructor not viable: requires 1 argument, but 2 were provided
      unique_ptr(const unique_ptr&) = delete;
      ^
1 error generated.

Answer 1

你可以转换return lock_scope（..）;返回std :: move（lock_scope（...））;

因为std :: unique_ptr :: operator =（const std :: unique_ptr＆amp;）是私有的;

Answer 2

声明您的lock_scope类型包含指向std::atomic<int>*的指针，即std::atomic<int>**。 free_lock声明和定义正确地反映了这一点。

但是你试图用lock_scope（一个间接较少）的指针初始化std::atomic<int>。

编译器消息相当清楚地表明：

[...] candidate constructor not viable: 
no known conversion from 'std::atomic *' to 'pointer' (aka 'std::atomic **') [...]

您需要为包装的lck添加一个额外的间接，或者更改lock_scope和free_lock以减少使用一个间接。

使用带有std :: unique_ptr的静态函数删除器时出错

2 个答案: