向量< auto_ptr<>的编译问题> [英] Compilation problems with vector<auto_ptr<> >

问题描述

请考虑以下代码：

  #include< iostream> 
 #include< memory> 
 #include< vector> 
 
 using namespace std; 
 
 struct A 
 {
 int a; 
 A（int a _）：a（a_）{} 
}; 
 
 int main（）
 {
 vector< auto_ptr< A> >如; 
 for（int i = 0; i <10; i ++）
 {
 auto_ptr< A> a（new A（i））; 
 as.push_back（a）; 
} 
 for（vector< auto_ptr< A>> :: iterator it = as.begin（）; it！= as.end（）; ++ it）
 cout< < （* it） - > a<< endl; 
} 
  

当试图编译它时，我从g ++得到以下模糊的编译器错误：

  g ++ -O0 -g3 -Wall -c -fmessage-length = 0-MMD -MP -MFsrc / proba。 d-MTsrc / proba.d-osrc / proba.o../src/proba.cpp
 /usr/include/c++/4.1.2/ext/new_allocator.h ：在成员函数'void __gnu_cxx :: new_allocator< _Tp> :: construct（_Tp *，const _Tp&）[with _Tp = std :: auto_ptr< A>]'：
 /usr/include/c++/4.1 .2 / bits / stl_vector.h：606：从'void std :: vector <_Tp，_Alloc> :: push_back（const _Tp&）实例化[with _Tp = std :: auto_ptr< A>，_Alloc = std :: allocator< ; std :: auto_ptr< A> >]'
 ../src/proba.cpp:19：从这里实例
 /usr/include/c++/4.1.2/ext/new_allocator.h:104：error：passing'const std :: auto_ptr< A>'as'this'参数'std :: auto_ptr< _Tp> :: operator std :: auto_ptr_ref< _Tp1>（）[with _Tp1 = A，_Tp = A]'丢弃限定符
 /usr/include/c++/4.1.2/bits/vector.tcc：在成员函数'void std :: vector< _Tp，_Alloc> :: _ M_insert_aux（__ gnu_cxx :: __ normal_iterator< typename std :: _ Vector_base< _Tp，_Alloc> ; :: _Tp_alloc_type :: pointer，std :: vector< _Tp，_Alloc>>>，const _Tp&）[with _Tp = std :: auto_ptr< A> ;, _Alloc = std :: allocator< std :: auto_ptr& >]'：
 /usr/include/c++/4.1.2/bits/stl_vector.h:610：从'void std :: vector <_Tp，_Alloc> :: push_back（const_Tp&与_Tp = std :: auto_ptr< A>，_Alloc = std :: allocator< std :: auto_ptr< A> >]'
 ../src/proba.cpp:19：从这里实例化
 /usr/include/c++/4.1.2/bits/vector.tcc:256：error：passing'const std :: auto_ptr< A>'as'this'参数'std :: auto_ptr< _Tp> :: operator std :: auto_ptr_ref< _Tp1>（）[with _Tp1 = A，_Tp = A]'丢弃限定符
 /usr/include/c++/4.1.2/bits/stl_construct.h：在函数'void std :: _Construct（_T1 *，const _T2&）[with _T1 = std :: auto_ptr< A>，_T2 = std： ：auto_ptr< A>]'：
 /usr/include/c++/4.1.2/bits/stl_uninitialized.h:86：从_ForwardIterator std :: __ uninitialized_copy_aux（_InputIterator，_InputIterator，_ForwardIterator，__false_type） _InputIterator = __gnu_cxx :: __ normal_iterator< std :: auto_ptr< A> *，std :: vector< std :: auto_ptr< A> ;, std :: allocator< std :: auto_ptr& > > >，_ForwardIterator = __gnu_cxx :: __ normal_iterator< std :: auto_ptr< A> *，std :: vector< std :: auto_ptr< A> ;, std :: allocator< std :: auto_ptr& > > >]'
 /usr/include/c++/4.1.2/bits/stl_uninitialized.h:113：从'_ForwardIterator std :: uninitialized_copy（_InputIterator，_InputIterator，_ForwardIterator）实例化[with _InputIterator = __gnu_cxx :: __ normal_iterator< ; std :: auto_ptr< A> *，std :: vector< std :: auto_ptr< A> ;, std :: allocator< std :: auto_ptr< A> > > >，_ForwardIterator = __gnu_cxx :: __ normal_iterator< std :: auto_ptr< A> *，std :: vector< std :: auto_ptr< A> ;, std :: allocator< std :: auto_ptr& > > >]'
 /usr/include/c++/4.1.2/bits/stl_uninitialized.h:254：从'_ForwardIterator std :: __ uninitialized_copy_a（_InputIterator，_InputIterator，_ForwardIterator，std :: allocator< _Tp>）实例化[with _InputIterator = __gnu_cxx :: __ normal_iterator< std :: auto_ptr< A> *，std :: vector< std :: auto_ptr< A> ;, std :: allocator< std :: auto_ptr& > > >，_ForwardIterator = __gnu_cxx :: __ normal_iterator< std :: auto_ptr< A> *，std :: vector< std :: auto_ptr< A> ;, std :: allocator< std :: auto_ptr& > > >，_Tp = std :: auto_ptr< A>]'
 /usr/include/c++/4.1.2/bits/vector.tcc:279：实例化为'void std :: vector< _Tp，_Alloc> :: _ M_insert_aux（__ gnu_cxx :: __ normal_iterator< typename std :: _ Vector_base< _Tp，_Alloc> :: _ Tp_alloc_type :: pointer，std :: vector< _Tp，_Alloc>>，const _Tp&）[with _Tp = std :: auto_ptr ; A>，_Alloc = std :: allocator< std :: auto_ptr< A> >]'
 /usr/include/c++/4.1.2/bits/stl_vector.h:610：实例化为'void std :: vector< _Tp，_Alloc> :: push_back（const _Tp& _Tp = std :: auto_ptr< A>，_Alloc = std :: allocator< std :: auto_ptr< A> >]'
 ../src/proba.cpp:19：从这里实例化
 /usr/include/c++/4.1.2/bits/stl_construct.h:81：error：passing'const std :: auto_ptr< A>'as'this'参数'std :: auto_ptr< _Tp> :: operator std :: auto_ptr_ref< _Tp1>（）[with _Tp1 = A，_Tp = A]'丢弃限定符
 make：*** [src / proba.o]错误1 
  

是const这里的一些问题。这是否意味着 auto_ptr 不能用于向量 s？

std :: auto_ptr 不能在 std :: vector 中使用 code>。

编译器抱怨有 auto_ptr 的赋值运算符更改对象正在分配，因此不能 const 。

您要使用 boost :: ptr_vector 或向量 boost :: shared_ptr s

Consider the following code:

#include <iostream>
#include <memory>
#include <vector>

using namespace std;

struct A
{
    int a;
    A(int a_):a(a_) {}
};

int main()
{
    vector<auto_ptr<A> > as;
    for (int i = 0; i < 10; i++)
    {
        auto_ptr<A> a(new A(i));
        as.push_back(a);
    }
    for (vector<auto_ptr<A> >::iterator it = as.begin(); it != as.end(); ++it)
        cout << (*it)->a << endl;
}

When trying to compile it, I get the following obscure compiler error from g++:

g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/proba.d" -MT"src/proba.d" -o"src/proba.o" "../src/proba.cpp"
/usr/include/c++/4.1.2/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = std::auto_ptr<A>]’:
/usr/include/c++/4.1.2/bits/stl_vector.h:606:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’
../src/proba.cpp:19:   instantiated from here
/usr/include/c++/4.1.2/ext/new_allocator.h:104: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers
/usr/include/c++/4.1.2/bits/vector.tcc: In member function ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’:
/usr/include/c++/4.1.2/bits/stl_vector.h:610:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’
../src/proba.cpp:19:   instantiated from here
/usr/include/c++/4.1.2/bits/vector.tcc:256: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers
/usr/include/c++/4.1.2/bits/stl_construct.h: In function ‘void std::_Construct(_T1*, const _T2&) [with _T1 = std::auto_ptr<A>, _T2 = std::auto_ptr<A>]’:
/usr/include/c++/4.1.2/bits/stl_uninitialized.h:86:   instantiated from ‘_ForwardIterator std::__uninitialized_copy_aux(_InputIterator, _InputIterator, _ForwardIterator, __false_type) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >]’
/usr/include/c++/4.1.2/bits/stl_uninitialized.h:113:   instantiated from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >]’
/usr/include/c++/4.1.2/bits/stl_uninitialized.h:254:   instantiated from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _Tp = std::auto_ptr<A>]’
/usr/include/c++/4.1.2/bits/vector.tcc:279:   instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’
/usr/include/c++/4.1.2/bits/stl_vector.h:610:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’
../src/proba.cpp:19:   instantiated from here
/usr/include/c++/4.1.2/bits/stl_construct.h:81: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers
make: *** [src/proba.o] Error 1

It seems to me that there is some kind of problem with consts here. Does this mean that auto_ptr can't be used in vectors?

解决方案

Correct, std::auto_ptr cannot be used in std::vector.

What the compiler is complaining about there is the assignment operator for auto_ptr changes the object being assigned from, and so it cannot be const.

You want to use either boost::ptr_vector or a vector of boost::shared_ptrs

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