我正在尝试过滤一个shared_ptr的容器,并试图将过滤后的内容保存在一个非所有者的容器中(weak_ptr)。在下面找到的程序崩溃。有人可以看到我在想什么吗?
#include <memory>
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <boost/bind.hpp>
struct A
{
int a_val;
explicit A():a_val(0) { std::cout << "A default constructed\n"; }
explicit A(int a):a_val(a) { std::cout << "A argument constructed\n"; }
A(const A& other) { a_val = other.a_val ; std::cout << "A copy constructed\n"; }
A& operator=(const A& other) { a_val = other.a_val ; std::cout << "A copy assigned\n"; return *this; }
~A() { std::cout << "A is destroyed\n"; }
struct a_visitor
{
std::vector < std::weak_ptr < A > > filtered_a;
a_visitor() { filtered_a.resize(0); }
void operator() (std::shared_ptr < A > a_ref)
{
if(a_ref->a_val % 2 )
filtered_a.push_back(a_ref);
}
};
std::function < void ( std::shared_ptr < A > ) > a_visit_function;
void visit_vector ( a_visitor *visitor)
{
a_visit_function = boost::bind(&a_visitor::operator(), visitor, _1);
std::shared_ptr< A > current_node(this);
a_visit_function(current_node);
}
};
int main(void)
{
std::vector < std::shared_ptr < A > > a_array;
for(int i=10;i<20;i++)
{
a_array.emplace_back(std::make_shared<A>(A(i)));
}
std::cout << "--------------------------\n";
std::for_each(a_array.begin(), a_array.end(), ([&]( std::shared_ptr<A> &a_ref){
std::cout << a_ref << " : " << a_ref->a_val << std::endl;
}));
std::cout << "--------------------------\n";
A::a_visitor visitor;
std::for_each(a_array.begin(), a_array.end(), ([&](std::shared_ptr < A > a_ref){
a_ref->visit_vector(&visitor);
}));
std::cout << "--------------------------\n";
std::for_each(visitor.filtered_a.begin(), visitor.filtered_a.end(), ([&](std::weak_ptr<A> &a_ref){
std::cout << a_ref.lock()->a_val << std::endl;
}));
std::cout << "--------------------------\n";
}
最佳答案
这是问题所在:std::shared_ptr< A > current_node(this);
。默认情况下,您只是无法做到这一点,this
具有自己的生命周期。另请:std::shared_ptr of this