使用 C++11 无限制联合时的 VS 2013 异常
VS 2013 exception when using C++11 unrestricted unions
考虑这段代码：
struct TNumeric {
bool Negative;
wstring Integral;
wstring Fraction;
};
union TValue {
// The unnamed structs are needed because otherwise the compiler does not accept it...
bool Bit;
struct{ TNumeric Numeric; };
struct{ wstring Text; };
};
TNumeric Numeric;
TNumeric &rNumeric{ Numeric };
rNumeric.Integral = L"";
rNumeric.Integral.push_back( L'X' ); //OK, no problem
TValue Value;
TValue &rValue{ Value };
rValue.Text = L"";
rValue.Text.push_back( L'X' ); //OK, no problem
rValue.Numeric.Integral = L"";
rValue.Numeric.Integral.push_back( L'X' ); // Exception
release模式下没有问题。当 运行 处于调试模式时，xutility 中 class _Iterator_base12 的方法_Adopt 的最后一条语句出现异常：Access violation reading location 0x0000005C。
在_Adopt 中代码只有运行 当_ITERATOR_DEBUG_LEVEL == 2。我试过
#define _ITERATOR_DEBUG_LEVEL 1
添加到我的主程序中，但它仍然定义为 2。
有没有办法禁用检查？
VS 2013 doesn't support C++11 unrestricted unions，即根据 C++03 实现联合：
An object
of a class with a non-trivial constructor (12.1), a non-trivial copy constructor (12.8), a non-trivial destructor
(12.4), or a non-trivial copy assignment operator (13.5.3, 12.8) cannot be a member of a union
你通过使用未命名的结构成功地欺骗了编译器，但这并没有解决问题：对象是非平凡的，而 VS2013 不支持它。
当您切换到更多 C++11 兼容的编译器（例如 VS 2015）时，您必须以安全的方式为联合实现构造函数、析构函数、复制构造函数等 constructs/destructs/copies 工会的适当部分。标准中有一个示例（我引用的是 C++14 草案 N4140 [class.union]/4）：
Consider an object u of a union type U having non-static data
members m of type M and n of type N. If M has a non-trivial destructor and N has a non-trivial constructor
(for instance, if they declare or inherit virtual functions), the active member of u can be safely switched
from m to n using the destructor and placement new operator as follows:
u.m.~M();
new (&u.n) N;
考虑这段代码：
struct TNumeric {
bool Negative;
wstring Integral;
wstring Fraction;
};
union TValue {
// The unnamed structs are needed because otherwise the compiler does not accept it...
bool Bit;
struct{ TNumeric Numeric; };
struct{ wstring Text; };
};
TNumeric Numeric;
TNumeric &rNumeric{ Numeric };
rNumeric.Integral = L"";
rNumeric.Integral.push_back( L'X' ); //OK, no problem
TValue Value;
TValue &rValue{ Value };
rValue.Text = L"";
rValue.Text.push_back( L'X' ); //OK, no problem
rValue.Numeric.Integral = L"";
rValue.Numeric.Integral.push_back( L'X' ); // Exception
release模式下没有问题。当 运行 处于调试模式时，xutility 中 class _Iterator_base12 的方法_Adopt 的最后一条语句出现异常：Access violation reading location 0x0000005C。
在_Adopt 中代码只有运行 当_ITERATOR_DEBUG_LEVEL == 2。我试过
#define _ITERATOR_DEBUG_LEVEL 1
添加到我的主程序中，但它仍然定义为 2。 有没有办法禁用检查？
VS 2013 doesn't support C++11 unrestricted unions，即根据 C++03 实现联合：
An object of a class with a non-trivial constructor (12.1), a non-trivial copy constructor (12.8), a non-trivial destructor (12.4), or a non-trivial copy assignment operator (13.5.3, 12.8) cannot be a member of a union
你通过使用未命名的结构成功地欺骗了编译器，但这并没有解决问题：对象是非平凡的，而 VS2013 不支持它。
当您切换到更多 C++11 兼容的编译器（例如 VS 2015）时，您必须以安全的方式为联合实现构造函数、析构函数、复制构造函数等 constructs/destructs/copies 工会的适当部分。标准中有一个示例（我引用的是 C++14 草案 N4140 [class.union]/4）：
Consider an object
uof a union typeUhaving non-static data membersmof typeMandnof typeN. IfMhas a non-trivial destructor andNhas a non-trivial constructor (for instance, if they declare or inherit virtual functions), the active member ofucan be safely switched frommtonusing the destructor and placement new operator as follows:u.m.~M(); new (&u.n) N;