c++ - 如何从 boost::ptr_vector 中删除元素

Question

所以我试图通过使用 boost::ptr_vector 摆脱我的 std::vector。现在我试图从一个元素中删除一个元素，并删除已删除的元素。对我来说最明显的事情是:

class A
{ int m; };

boost::ptr_vector<A> vec;
A* a = new A;
vec.push_back(a);
vec.erase(a);

但这甚至无法编译(完整的错误信息见下文)。我已经像在 std::vector 上一样尝试了删除/删除习惯用法，但 boost::ptr_vector 的所有算法结果都与 std::vector 中的算法略有不同。

所以我的问题:

• 如何从 ptr_vector 中删除指针？
• 我是否还需要手动 delete() 我删除的那个元素？

编译器错误:

1>------ Build started: Project: ptr_vector_test, Configuration: Debug Win32 ------
1>Compiling...
1>ptr_vector_test.cpp
1>c:\users\rvanhout\svn\trunk\thirdparty\boost\range\const_iterator.hpp(37) : error C2825: 'C': must be a class or namespace when followed by '::'
1>        c:\users\rvanhout\svn\trunk\thirdparty\boost\mpl\eval_if.hpp(63) : see reference to class template instantiation 'boost::range_const_iterator<C>' being compiled
1>        with
1>        [
1>            C=A *
1>        ]
1>        c:\users\rvanhout\svn\trunk\thirdparty\boost\range\iterator.hpp(63) : see reference to class template instantiation 'boost::mpl::eval_if_c<C,F1,F2>' being compiled
1>        with
1>        [
1>            C=true,
1>            F1=boost::range_const_iterator<A *>,
1>            F2=boost::range_mutable_iterator<A *const >
1>        ]
1>        c:\users\rvanhout\svn\trunk\thirdparty\boost\ptr_container\detail\reversible_ptr_container.hpp(506) : see reference to class template instantiation 'boost::range_iterator<C>' being compiled
1>        with
1>        [
1>            C=A *const 
1>        ]
1>        c:\tmp\ptr_vector_test\ptr_vector_test.cpp(21) : see reference to function template instantiation 'boost::void_ptr_iterator<VoidIter,T> boost::ptr_container_detail::reversible_ptr_container<Config,CloneAllocator>::erase<A*>(const Range &)' being compiled
1>        with
1>        [
1>            VoidIter=std::_Vector_iterator<void *,std::allocator<void *>>,
1>            T=A,
1>            Config=boost::ptr_container_detail::sequence_config<A,std::vector<void *,std::allocator<void *>>>,
1>            CloneAllocator=boost::heap_clone_allocator,
1>            Range=A *
1>        ]
1>c:\users\rvanhout\svn\trunk\thirdparty\boost\range\const_iterator.hpp(37) : error C2039: 'const_iterator' : is not a member of '`global namespace''
1>c:\users\rvanhout\svn\trunk\thirdparty\boost\range\const_iterator.hpp(37) : error C2146: syntax error : missing ';' before identifier 'type'
1>c:\users\rvanhout\svn\trunk\thirdparty\boost\range\const_iterator.hpp(37) : error C2208: 'boost::type' : no members defined using this type
1>c:\users\rvanhout\svn\trunk\thirdparty\boost\range\const_iterator.hpp(37) : fatal error C1903: unable to recover from previous error(s); stopping compilation
1>Build log was saved at "file://c:\tmp\ptr_vector_test\Debug\BuildLog.htm"
1>ptr_vector_test - 5 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

你也可以用 std::vector 来做到这一点。

在这两种情况下，erase 都将迭代器作为参数。
因此，在从 vector (或 ptr_vector)中删除某些内容之前，您需要找到它。

另请注意，ptr_vector 将其内容视为您存储的对象而非指针。所以任何搜索都是通过对象完成的。

基本上是这样

 std::vector<A>       x;
 std::ptr_vector<A>   y;

 // These two object should behave in exactly the same way.
 // The ONLY difference is inserting values which for y are pointers.
 // Y take ownership of the pointer and all subsequent acesses to the
 // members of y look like they are objects

例子:

#include <boost/ptr_container/ptr_vector.hpp>
#include <vector>

class A
{ int m;
    public:
    A(int x):m(x)   {}
    bool operator==(A const& rhs)   {return m = rhs.m;}
};

int main()
{
    boost::ptr_vector<A>    x;
    x.push_back(new A(1));
    x.erase(std::find(x.begin(),x.end(),A(1)));


    std::vector<A>          y;
    y.push_back(A(2));
    y.erase(std::find(y.begin(),y.end(),A(2)));

    // To find an exact pointer don't modify the equality.
    // Use find_if and pass a predicate that tests for a pointer
    A* a = new A(3);
    boost:ptr_Vector<A>     z;
    z.push_back(a);
    z.erase(std::find_if(y.begin(),y.end(),CheckPointerValue(a));
}

struct CheckPointerValue
{
     CheckPointerValue(A* a):anA(a) {}
     bool operator()(A const& x)    { return &X == anA;}
     private:
        A* anA;
};