Question

此代码无法使用g ++ 4.2.1进行编译，但在vc ++ v8下工作正常。

#include <set>
typedef std::set<int *> IntPtrSet;
IntPtrSet iptrSet;

typedef std::set<shared_ptr<int>> IntPtrSet2;
IntPtrSet2 iptrSet2;

void AddIntegers(int& x)
{
    iptrSet.insert(&x);
    iptrSet2.insert(&x);
}

shared_ptr类似于boost :: shared_ptr或tr1 :: shared_ptr。

它会发出以下错误，

No matching function for call to std::allocator<shared_ptr<int>>::construct(int**, const shared_ptr<int>&)
No matching function for call to std::allocator<shared_ptr<int> >::destroy(int **)

之前有没有人遇到过这样的错误？如果是，那么解决方法是什么。

以下是完整的错误消息：

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:402: error: no matching function for call to 'std::allocator<shared_ptr<int> >::destroy(int**)'

/Users/mark/Templates/Function/main.cpp:188:   instantiated from here
/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:380: error: no matching function for call to 'std::allocator<shared_ptr<int> >::construct(int**, const shared_ptr<int>&)'
/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/ext/new_allocator.h:106: note: candidates are: void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = shared_ptr<int>]

完整的模板实例化堆栈：

/Developer/usr/bin/gcc-4.2 -x c++ -arch x86_64 -fmessage-length=0 -pipe -Wno-trigraphs -fpascal-strings -fasm-blocks -O0 -Wreturn-type -Wunused-variable -isysroot 
/Developer/SDKs/MacOSX10.6.sdk -mfix-and-continue -fvisibility-inlines-hidden -mmacosx-version-min=10.6 -gdwarf-2 -iquote   /Users/mark/Templates/Function/build/Function.build/Debug/Function.build/Function-generated-files.hmap - I/Users/mark/Templates/Function/build/Function.build/Debug/Function.build/Function-own-target-headers.hmap - I/Users/mark/Templates/Function/build/Function.build/Debug/Function.build/Function-all- target-headers.hmap -iquote  /Users/mark/Templates/Function/build/Function.build/Debug/Function.build/Function-project- headers.hmap -F/Users/mark/Templates/Function/build/Debug - I/Users/mark/Templates/Function/build/Debug/include - I/Users/mark/Templates/Function/build/Function.build/Debug/Function.build/DerivedSources/x86 _64 - I/Users/mark/Templates/Function/build/Function.build/Debug/Function.build/DerivedSources -c  /Users/mark/Templates/Function/main.cpp -o  /Users/mark/Templates/Function/build/Function.build/Debug/Function.build/Objects- normal/x86_64/main.o

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h: In member function 'void std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_destroy_node(std::_Rb_tree_node<_Val>*) [with _Key = shared_ptr<int>, _Val = shared_ptr<int>, _KeyOfValue = std::_Identity<shared_ptr<int> >, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]':

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:1327:   instantiated from 'void std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_erase(std::_Rb_tree_node<_Val>*) [with _Key = shared_ptr<int>, _Val = shared_ptr<int>, _KeyOfValue = std::_Identity<shared_ptr<int> >, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]'

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:594:   instantiated from 'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::~_Rb_tree() [with _Key = shared_ptr<int>, _Val = shared_ptr<int>, _KeyOfValue = std::_Identity<shared_ptr<int> >, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]'

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_set.h:141:   instantiated from 'std::set<_Key, _Compare, _Alloc>::set() [with _Key = shared_ptr<int>, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]'

/Users/mark/Templates/Function/main.cpp:181：从这里实例化

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:402: error: no matching function for call to 'std::allocator<shared_ptr<int> >::destroy(int**)'

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/ext/new_allocator.h:110: note: candidates are: void __gnu_cxx::new_allocator<_Tp>::destroy(_Tp*) [with _Tp = shared_ptr<int>]

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h: In member function 'std::_Rb_tree_node<_Val>* std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_create_node(const _Val&) [with _Key = shared_ptr<int>, _Val = shared_ptr<int>, _KeyOfValue = std::_Identity<shared_ptr<int> >, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]':

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:840:   instantiated from 'typename std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert(std::_Rb_tree_node_base*, std::_Rb_tree_node_base*, const _Val&) [with _Key = shared_ptr<int>, _Val = shared_ptr<int>, _KeyOfValue = std::_Identity<shared_ptr<int> >, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]'

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:988:   instantiated from 'std::pair<typename std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(const _Val&) [with _Key = shared_ptr<int>, _Val = shared_ptr<int>, _KeyOfValue = std::_Identity<shared_ptr<int> >, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]'

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_set.h:307:   instantiated from 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, typename _Alloc::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(const _Key&) [with _Key = shared_ptr<int>, _Compare = std::less<shared_ptr<int> >, _Alloc = std::allocator<shared_ptr<int> >]'

/Users/mark/Templates/Function/main.cpp:188:   instantiated from here

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/bits/stl_tree.h:380: error: no matching function for call to 'std::allocator<shared_ptr<int> >::construct(int**, const shared_ptr<int>&)'

/Developer/SDKs/MacOSX10.6.sdk/usr/include/c++/4.2.1/ext/new_allocator.h:106: note: candidates are: void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = shared_ptr<int>]

以下是完整的代码：

#include <iostream>
template <class T>
class shared_ptr
{
    private:
    T* m_p;
public:
shared_ptr() throw() : m_p(NULL){}

shared_ptr( const shared_ptr<T>& p) throw()
{
      m_p = p;
}

shared_ptr( T* p) throw()
{
    m_p = p;
}

~shared_ptr() throw()
{
    m_p = NULL;
}

T* operator=(const shared_ptr<T>& p) throw()
{
    if (m_p != p.m_p)
    {
        m_p = p;
    }
    return m_p;
}

T* operator=(T* p) throw()
{
    if (m_p != p)
    {
        m_p = p;
    }
    return m_p;
}

operator T*() const throw()
{
    return m_p;
}

T& operator*() const throw()
{
    return *m_p;
}

T** operator&() throw()
{
    return &m_p;
}

bool operator!() const throw()
{
    return (m_p == NULL);
}

bool operator<(T* p) const throw()
{
    return m_p < p;
}

bool operator!=(int nNull) const throw()
{
    return !operator==(nNull);
}

bool operator==( int nNull) const throw()
{
    return m_p == NULL;
}

bool operator!=( T* p) const throw()
{
    return !operator==(p);
}

bool operator==( T* p) const throw()
{
    return m_p == p;
}

void CopyTo( T** pp) const throw()
{
    *pp = m_p;
}

void Release() throw()
{
    T* p = m_p;
    if (p)
    {
        m_p = NULL;
    }
}

void Attach( T* p) throw()
{
    m_p = p;
}

T* Detach() throw()
{
    T* p = m_p;
    m_p = NULL;
    return p;
}

};

#include <set>
typedef std::set<int *> IntPtrSet;
IntPtrSet iptrSet;

typedef std::set<shared_ptr<int> > IntPtrSet2;
IntPtrSet2 iptrSet2;

void AddIntegers(int& x)
{
iptrSet.insert(&x);

shared_ptr<int> intPtr(new int(3));

iptrSet2.insert(intPtr);
}


int main (int argc, char * const argv[]) {


char c;
std::cin >> c;
    return 0;
}

同样在Dinkumware网站上，代码编译成功。如前所述，它无法使用g ++进行编译。对不起，我已经粘贴了下面的Dinkumware网站（http://www.dinkumware.com/exam/default.aspx）的结果。

您的代码是使用Microsoft Visual Studio 2005 C ++编译器编译的来自Dinkum Compleat Libraries for VC ++包的Dinkum C ++库。

这是在名为的文件中使用上述代码的编译器输出 sourceFile.cpp：

sourceFile.cpp

size sourceFile.exe： 6144t + 3584 .rdata + 512d = 10240（2800）

代码编译成功！生成的可执行文件是11 KB。

非常感谢

此致标记

Answer 1

对于（显而易见的）原因，没有从T*到shared_ptr<T>的隐式转换。

例如，以下代码失败：

int i = 3;
shared_ptr<int> ptr;
ptr = &i;

有一个很好的理由：shared_ptr OWNS指出的资源。你不能盲目地将某些东西扔进shared_ptr以获得免费的内存管理，你必须确保该对象还没有被其他东西拥有。

解决方案是使用构造函数或构建器：

shared_ptr<int> ptr(new int(3));

shared_ptr<int> ptr = shared_ptr<int>(new int(3));

shared_ptr<int> made = make_shared<int>(3);

最后一种方法会导致指针稍微紧凑，但这种差异不太可能影响你。

我会强调你的榜样是可疑的。在创建时，所有权更好地执行。在这样的功能中，很可能其他人已经获得了所有权，并且您正在创建一个大错误。

Answer 2

您的shared_ptr实施似乎非常不寻常。

与boost / tr1相比，您有T **和T *的额外转换运算符。隐式转换为底层指针类型（T *）只会让编译器感到困惑。

在我评论出这些方法之后，我不得不修复复制构造函数以实际复制成员而不是滥用转换运算符。它仍然无法作为共享指针工作，因为没有引用计数。

然后我必须修复operator<再次使用const shared_ptr<T>& p，因为隐式转换导致编译，但稍后会混淆std::set上的编译器。它感到困惑，因为它试图构造shared_ptr，但operator&（我认为）导致它降级为T**，因此类型与容器内的类型不匹配。 / p>

通过这些更改，我能够使用g ++ 4.2成功编译。

编辑：好吧，我能够编写一个自定义分配器，但它看起来并不是很干净，甚至可能无法在所有情况下工作。

template <class T>
class sh_ptr_alloc : public std::allocator<T>
{
public:
        typedef size_t     size_type;

      sh_ptr_alloc() throw() { }

      template<typename Tp1>
        sh_ptr_alloc(const sh_ptr_alloc<Tp1>&) throw() { }

      template<typename Tp1>
        struct rebind
        { typedef sh_ptr_alloc<Tp1> other; };

template <class Tp1>
      void
      deallocate(Tp1* p, size_type)
      { ::operator delete(p); }

template <class Tp1>
      void 
      construct(Tp1** p, const shared_ptr<Tp1>& val) 
      { ::new(p) shared_ptr<int>(val); }

template <class Tp1>
      void 
      destroy(Tp1** p) { }
};

该集合是：

typedef std::set<shared_ptr<int>, std::less<shared_ptr<int> >, sh_ptr_alloc<shared_ptr<int> > > IntPtrSet2;

Answer 3

看起来它在从int *到shared_ptr的转换时遇到了麻烦。我认为解决方法非常简单：

shared_ptr<int> intPtr(&x);
iptrSet2.insert(intPtr);

Answer 4

void AddIntegers(int& x)
{
...
    iptrSet2.insert(&x);

这可能会失败，因为int*到boost::shared_ptr<int>没有隐式转换形式。你必须手动构建它（并注意：对于一个对象，只能构造一个shared_ptr;其他指针必须作为这个“master”共享指针的副本创建。）

gcc解决方法，同时使用shared_ptr插入std :: set

4 个答案: