Posted on 2011-03-08 19:58
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02 編程語言
boost::unsafe_any_cast：類型強制轉換，不考慮原來的any的類型
// Note: The "unsafe" versions of any_cast are not part of the
// public interface and may be removed at any time. They are
// required where we know what type is stored in the any and can't
// use typeid() comparison, e.g., when our types may travel across
// different shared libraries.
template<typename ValueType>
inline ValueType * unsafe_any_cast(any * operand)
{
return &static_cast<any::holder<ValueType> *>(operand->content)->held;
}
template<typename ValueType>
inline const ValueType * unsafe_any_cast(const any * operand)
{
return unsafe_any_cast<ValueType>(const_cast<any *>(operand));
}
boost::any_cast：必須和存的類型一致，否則報錯
template<typename ValueType>
ValueType * any_cast(any * operand)
{
return operand &&
#ifdef BOOST_AUX_ANY_TYPE_ID_NAME
std::strcmp(operand->type().name(), typeid(ValueType).name()) == 0
#else
operand->type() == typeid(ValueType)
#endif
? &static_cast<any::holder<ValueType> *>(operand->content)->held
: 0;
}
template<typename ValueType>
inline const ValueType * any_cast(const any * operand)
{
return any_cast<ValueType>(const_cast<any *>(operand));
}
template<typename ValueType>
ValueType any_cast(any & operand)
{
typedef BOOST_DEDUCED_TYPENAME remove_reference<ValueType>::type nonref;
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
// If 'nonref' is still reference type, it means the user has not
// specialized 'remove_reference'.
// Please use BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION macro
// to generate specialization of remove_reference for your class
// See type traits library documentation for details
BOOST_STATIC_ASSERT(!is_reference<nonref>::value);
#endif
nonref * result = any_cast<nonref>(&operand);
if(!result)
boost::throw_exception(bad_any_cast());
return *result;
}
template<typename ValueType>
inline ValueType any_cast(const any & operand)
{
typedef BOOST_DEDUCED_TYPENAME remove_reference<ValueType>::type nonref;
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
// The comment in the above version of 'any_cast' explains when this
// assert is fired and what to do.
BOOST_STATIC_ASSERT(!is_reference<nonref>::value);
#endif
return any_cast<const nonref &>(const_cast<any &>(operand));
}
用法：
String abcd = "1.0";
boost::any test = abcd;
float abc = boost::any_cast<float>(test);//報錯
float abc1 = *boost::unsafe_any_cast<float>(&test);//結果也不對, 存什么類型，取出來必須強制轉換為什么類型