我的代码中有一个非常奇怪的错误,并设法将其简化为以下单个函数。
#include "either.hpp"
#include <string>
#include <iostream>
#include <vector>
#include <functional>
int main()
{
using std::string;
using std::vector;
auto callback = []()
{
auto either = data::either<string,vector<int>>(string("test"));
return either;
return data::either<string,vector<int>>(string("test"));
};
callback();
}
std::string
运行时,此程序会在' 的析构函数上生成分段错误。但是,如果我们删除第二return
条语句,它就可以完美运行。
现在,data::either
该类使用具有两个成员的联合,并且 lambda 的 return 语句将导致堆栈分配变量的破坏。
我对这些功能的使用是否存在问题,是由于我不知道的原因导致的未定义行为,还是仅仅是编译器错误?
这是either
课程:
#ifndef EITHER_HPP
#define EITHER_HPP
#include <cassert>
#include <functional>
#include <type_traits>
#include <utility>
// Model the haskel Data.Either data type.
// http://hackage.haskell.org/package/base-4.6.0.1/docs/Data-Either.html
namespace data
{
template<class Left, class Right>
class either
{
static_assert(
!std::is_same<
typename std::remove_cv<Left>::type,
typename std::remove_cv<Right>::type
>::value,
"data::either<A,B>: type A and B must be different.");
bool m_is_right;
union
{
Left m_left;
Right m_right;
};
public:
explicit either(Left l)
: m_is_right(false)
, m_left(std::move(l))
{
}
explicit either(Right r)
: m_is_right(true)
, m_right(std::move(r))
{
}
either(either const& other)
: m_is_right(other.is_right())
{
if (other.is_left())
{
m_left = other.left();
}
else
{
m_right = other.right();
}
}
either(either&& other)
: m_is_right(other.is_right())
{
if (other.is_left())
{
m_left = std::move(other.left());
}
else
{
m_right = std::move(other.right());
}
}
~either()
{
if (is_right())
{
right().~Right();
}
else
{
left().~Left();
}
}
either& operator=(either const& other)
{
m_is_right = other.is_right();
if (other.is_left())
{
m_left = other.left();
}
else
{
m_right = other.right();
}
return *this;
}
either& operator=(either&& other)
{
m_is_right = other.is_right();
if (other.is_left())
{
m_left = std::move(other.left());
}
else
{
m_right = std::move(other.right());
}
return *this;
}
bool is_left() const
{
return !is_right();
}
bool is_right() const
{
return m_is_right;
}
Left& left()
{
assert(is_left());
return m_left;
}
Left const& left() const
{
assert(is_left());
return m_left;
}
Right& right()
{
assert(is_right());
return m_right;
}
Right const& right() const
{
assert(is_right());
return m_right;
}
};
}
#endif
我使用以下编译器对其进行了测试:
$ clang++ -std=c++11 test.cpp && ./a.out
Segmentation fault
$ clang++ --version
Debian clang version 3.2-11 (tags/RELEASE_32/final) (based on LLVM 3.2)
Target: x86_64-pc-linux-gnu
Thread model: posix
$ g++ -std=c++11 test.cpp && ./a.out
Segmentation fault
$ g++ --version
g++ (Debian 4.7.3-4) 4.7.3
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.