Question

这次我正在尝试使用分配器。我觉得有很多机会泄漏资源。所以我想如果我使用std::unique_ptr来处理它们会怎样。我用std::vector的分配器试了一下手。我的代码是这样的： -

// allocator
#include <iostream>
#include <vector>
#include <memory>
using namespace std;

class X
{
    int x,ID;
    static int i;
    public:
        X()
        {
            cout<<"constructing ";
            ID=++i;
            cout<<"ID="<<ID<<'\n';
        }
        X(int a)
        {
            x=a;
            cout<<"constructing ";
            ID=++i;
            cout<<"ID="<<ID<<'\n';
        }
        void get()
        {
            cout<<"enter x: ";
            cin>>x;
        }
        void disp()
        {
            cout<<"x="<<x<<'\t';
        }
        ~X()
        {
            cout<<"destroying ID="<<ID<<'\n';
        }
};
int X:: i=0;

int main()
{
    ios::sync_with_stdio(false);
    vector<X> v;
    auto alloc = v.get_allocator();
    unsigned int i=0;

    X *p(alloc.allocate(5));        
    for (i=0;i<5;++i)
    alloc.construct (&p[i], i+1);
    unique_ptr<X[]> ptr(p);

    cout<<"\nthe elements are:-\n";
    for (i=0;i<5;++i)
    {
        ptr[i].disp();
        cout << '\t' << (long long)alloc.address(ptr[i]) << '\n';
    }
    cout<<"\n";

    /*for (i=0;i<5;++i)
    alloc.destroy(&p[i]);
    deallocate(p,16)*/

    return 0;
}

不幸的是，此代码崩溃显示UB。所以我该怎么做？我应该如何操纵我的代码以使其适合std::unique_ptr？

Answer 1

template<typename T, typename... Args>
std::unique_ptr<T[], std::function<void(T *)>> make_T_Construct(std::allocator<T> alloc, std::size_t size, Args... args) {

    X *ptr = alloc.allocate(size);

    for (std::size_t i = 0; i < size; ++i) {
        alloc.construct(&ptr[i], std::forward<Args>(args)...);
    }


    auto deleter = [](T *p, std::allocator<T> alloc, std::size_t size) {
        for (std::size_t i = 0; i < size; ++i) {
            alloc.destroy(&p[i]);
        }
        alloc.deallocate(p, sizeof(T) * size);
    };

    return {ptr, std::bind(deleter, std::placeholders::_1, alloc, size)};
}

int main(int argc, const char * argv[]) {
    std::allocator<X> alloc = std::allocator<X>();

    auto ptr = make_T(alloc, 5, 100);

    return 0;
}

也可以写一个来为你构建对象：

template<typename T>
struct Allocator
{
    typedef T value_type;

    Allocator() noexcept {};

    template<typename U>
    Allocator(const Allocator<U>& other) throw() {};

    T* allocate(std::size_t n, const void* hint = 0)
    {
        T* memory = static_cast<T*>(::operator new(n * (sizeof(T) + sizeof(bool))));

        for (std::size_t i = 0; i < n * (sizeof(T) + sizeof(bool)); ++i)
        {
            *reinterpret_cast<bool*>(reinterpret_cast<char*>(memory) + sizeof(bool)) = false;
        }

        return memory;
    }

    void deallocate(T* ptr, std::size_t n)
    {
        ::operator delete(ptr);
    }

    void construct(T* p, const T& arg)
    {
        destroy(p);
        new(p) T(arg);
        *reinterpret_cast<bool*>(reinterpret_cast<char*>(p) + sizeof(bool)) = true;
    }

    template<class U, class... Args>
    void construct(U* p, Args&&... args)
    {
        destroy(p);
        ::new(p) U(std::forward<Args>(args)...);

        *reinterpret_cast<bool*>(reinterpret_cast<char*>(p) + sizeof(bool)) = true;
    }

    void destroy(T* p)
    {
        if (*reinterpret_cast<bool*>(reinterpret_cast<char*>(p) + sizeof(bool))) {
            p->~T();
            *reinterpret_cast<bool*>(reinterpret_cast<char*>(p) + sizeof(bool)) = false;
        }
    }

    template<class U>
    void destroy(U* p)
    {
        if (*reinterpret_cast<bool*>(reinterpret_cast<char*>(p) + sizeof(bool))) {
            p->~U();
            *reinterpret_cast<bool*>(reinterpret_cast<char*>(p) + sizeof(bool)) = false;
        }
    }
};

template <typename T, typename U>
inline bool operator == (const Allocator<T>&, const Allocator<U>&)
{
    return true;
}

template <typename T, typename U>
inline bool operator != (const Allocator<T>& a, const Allocator<U>& b)
{
    return !(a == b);
}

编辑：要执行您想要的操作（跟踪分配），您必须使用自定义分配器自行跟踪内存分配。

a[i] = (nr % 10) % 2 == 0 ? nr % 10 + 1 : nr % 10;

将std :: unique_ptr与分配器

1 个答案: