编辑：事实证明这是临时人员的问题。基本上，我无知地使用 C++，就好像它像 Java 或 C# 一样工作，但事实并非如此。希望这将是一个很好的警示故事。
编辑：这个问题似乎只发生在 和 的组合joint_view中shared_ptr。原始指针似乎在相同的场景中工作得很好，就像一个普通的融合容器中的共享指针一样，它一次构建了它的所有项目，而不向它添加任何东西。详情如下：
我正在使用 mingw gcc 4.5.1
在使用 boost fusion 容器并取回内容时遇到一个特殊问题。我有一个自定义类，它被包裹在 a 中std::shared_ptr，然后将其交给 fusion make_list()（或者make_vector()，似乎无关紧要）。如果我可以一次将所有对象放入容器中，那一切都很好。当我向容器添加另一个共享指针时，问题似乎出现了，这会产生一个joint_view. 我使用 a 进行迭代fusion::for_each()并传入一个函数对象以打印出该值。如果我正在迭代共享指针的普通融合容器，而不是 ajoint_view或joint_view其中没有共享指针的 a ，它可以正常工作，但否则会出现分段错误或垃圾值。
以下是我为尝试隔离我的问题而编写的测试程序。关于问题可能是什么的任何想法？完全有可能我只是错过了我应该/不应该做的事情:(
#include <iostream>
#include <memory>
//BOOST SMART POINTERS
//I only use boost's shared_ptr for ONE test, results are the same.
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
//BOOST FUSION
#include <boost/fusion/algorithm/iteration/for_each.hpp>
#include <boost/fusion/include/for_each.hpp>
#include <boost/fusion/container/generation/make_list.hpp>
#include <boost/fusion/include/make_list.hpp>
#include <boost/fusion/container/generation/make_vector.hpp>
#include <boost/fusion/include/make_vector.hpp>
#include <boost/fusion/algorithm/transformation/push_back.hpp>
#include <boost/fusion/include/push_back.hpp>
using namespace std;
using namespace boost::fusion;
struct TestStructInt {
int test_int;
TestStructInt(int init_num) : test_int(init_num) {};
};
struct TestStructString {
string test_string;
TestStructString(string init_str) : test_string(init_str) {};
};
struct do_junk{
void operator()(string t) const {
cout << t << endl;
}
void operator()(string* t) const {
cout << *t << endl;
}
void operator()(std::shared_ptr<int> t) const {
cout << *t << endl;
}
void operator()(std::shared_ptr<string> t) const {
cout << *t << endl;
}
void operator() (boost::shared_ptr<string> t) const {
cout << *t << endl;
}
void operator() (TestStructInt t) const {
cout << t.test_int << endl;
}
void operator() (std::shared_ptr<TestStructInt> t) const {
cout << t->test_int << endl;
}
void operator() (TestStructString t) const {
cout << t.test_string << endl;
}
void operator() (std::shared_ptr<TestStructString> t) const {
cout << t->test_string << endl;
}
void operator() (std::shared_ptr<TestStructString*> t) const {
cout << (*t)->test_string << endl;
}
};
int main()
{
string foo1 = "foo1";
string foo2 = "foo2";
string foo3 = "foo3";
int bar1 = 1;
int bar2 = 2;
int bar3 = 3;
string* foo1_ptr = &foo1;
string* foo2_ptr = &foo2;
string* foo3_ptr = &foo3;
auto foo1_obj = make_shared<TestStructString>(TestStructString("foo1"));
auto foo2_obj = make_shared<TestStructString>(TestStructString("foo2"));
auto foo3_obj = make_shared<TestStructString>(TestStructString("foo3"));
//works fine
auto list_test1 = make_list(foo1, foo2);
//works fine
auto list_test2 = make_list(foo1_ptr, foo2_ptr);
//seems to work, but is undefined behavior
auto list_test3
= make_list(
std::make_shared<int>(bar1), std::make_shared<int>(bar2)
)
;
//seems to work, but is undefined behavior
auto list_test4
= make_list(
std::make_shared<string>(foo1), std::make_shared<string>(foo2)
)
;
//seems to work, but is undefined behavior
auto list_test5
= make_list(
std::make_shared<TestStructInt>(TestStructInt(1))
, std::make_shared<TestStructInt>(TestStructInt(2))
)
;
//seems to work, but is undefined behavior
auto list_test6
= make_list(
std::make_shared<TestStructString>(TestStructString("foo1"))
, std::make_shared<TestStructString>(TestStructString("foo2"))
)
;
//seems to work, but is undefined behavior
auto list_test7
= make_list(TestStructString("foo1"), TestStructString("foo2"))
;
//seems to work, but is undefined behavior
auto joint_view_test1 = push_back(make_list(foo1, foo2), foo3);
//seems to work, but is undefined behavior
auto joint_view_test2 = push_back(make_list(foo1_ptr, foo2_ptr), foo3_ptr);
//seems to work, but is undefined behavior
auto joint_view_test3
= push_back(
make_list(
TestStructString(foo1), TestStructString(foo2)
)
, TestStructString(foo3)
)
;
//integer values I pass in are coming out different
auto joint_view_test4
= push_back(
make_list(
std::make_shared<int>(bar1), std::make_shared<int>(bar2)
)
, make_shared<int>(bar3)
)
;
//pass in foo1, foo2, and foo3, but only get foo3's value back out for each
auto joint_view_test5
= push_back(
make_list(
std::make_shared<string>(foo1), std::make_shared<string>(foo2)
)
, make_shared<string>(foo3)
)
;
//causes seg fault when running do_junk()
auto joint_view_test6
= push_back(
make_vector(
std::make_shared<string>(foo1), std::make_shared<string>(foo2)
)
, std::make_shared<string>(foo3)
)
;
//causes seg fault when running do_junk()
auto joint_view_test7
= push_back(
make_list(
boost::make_shared<string>(foo1)
, boost::make_shared<string>(foo2)
)
, boost::make_shared<string>(foo3)
)
;
//integer values I pass in are coming out different
auto joint_view_test8
= push_back(
make_list(
std::make_shared<TestStructInt>(TestStructInt(1))
, std::make_shared<TestStructInt>(TestStructInt(2))
)
, std::make_shared<TestStructInt>(TestStructInt(3))
)
;
//causes seg fault when running do_junk()
auto joint_view_test9
= push_back(
make_list(
std::make_shared<TestStructString>(TestStructString("foo1"))
, std::make_shared<TestStructString>(TestStructString("foo2"))
)
, std::make_shared<TestStructString>(TestStructString("foo3"))
)
;
//causes seg fault when running do_junk()
auto joint_view_test10
= push_back(
make_list(
std::make_shared<TestStructString*>(new TestStructString("foo1"))
, std::make_shared<TestStructString*>(new TestStructString("foo2"))
)
, std::make_shared<TestStructString*>(new TestStructString("foo3"))
)
;
//seems to work, but is undefined behavior
auto joint_view_test11
= push_back(
make_list(
foo1_obj
, foo2_obj
)
, foo3_obj
)
;
cout << "@@ list1" << endl;
boost::fusion::for_each(list_test1, do_junk());
cout << "@@ list2" << endl;
boost::fusion::for_each(list_test2, do_junk());
cout << "@@ list3" << endl;
boost::fusion::for_each(list_test3, do_junk());
cout << "@@ list4" << endl;
boost::fusion::for_each(list_test4, do_junk());
cout << "@@ list5" << endl;
boost::fusion::for_each(list_test5, do_junk());
cout << "@@ list6" << endl;
boost::fusion::for_each(list_test6, do_junk());
cout << "@@ list7" << endl;
boost::fusion::for_each(list_test7, do_junk());
cout << "@@ joint_view1" << endl;
boost::fusion::for_each(joint_view_test1, do_junk());
cout << "@@ joint_view2" << endl;
boost::fusion::for_each(joint_view_test2, do_junk());
cout << "@@ joint_view3" << endl;
boost::fusion::for_each(joint_view_test3, do_junk());
cout << "@@ joint_view4" << endl;
boost::fusion::for_each(joint_view_test4, do_junk());
cout << "@@ joint_view5" << endl;
//boost::fusion::for_each(joint_view_test5, do_junk());
cout << "@@ joint_view6" << endl;
//boost::fusion::for_each(joint_view_test6, do_junk());
cout << "@@ joint_view7" << endl;
//boost::fusion::for_each(joint_view_test7, do_junk());
cout << "@@ joint_view8" << endl;
//boost::fusion::for_each(joint_view_test8, do_junk());
cout << "@@ joint_view9" << endl;
//boost::fusion::for_each(joint_view_test9, do_junk());
cout << "@@ joint_view10" << endl;
//boost::fusion::for_each(joint_view_test10, do_junk());
cout << "@@ joint_view11" << endl;
boost::fusion::for_each(joint_view_test11, do_junk());
cout << "@@" << endl;
return 0;
}