升压类的序列化,在成员类型的变化 [英] Boost class serialization, change in member types
问题描述
一个人如何手柄开关系列化成员的类型,而保持与previous存档的兼容性?例如。我想改变浮法/ INT
到双/为size_t
。
How does one handle switching the type of serialized members while retaining compatability with previous archive? E.g. I want to change float/int
to double/size_t
.
我知道我可以递增版本号,但使code凌乱。是否有不同的方式来处理这个问题?如果它使不同,成员被序列直通 MAKE_NVP
。
I know I can increment version number but that makes code messy. Is there a different way to handle that? If it makes difference, the members are serialized thru MAKE_NVP
.
推荐答案
您可以使用版本
参数版本。文档给出了这样的例子:的http://www.boost.org/doc/libs/1_55_0/libs/serialization/doc/tutorial.html#versioning
You can use the version
parameter to version. The documentation gives this example: http://www.boost.org/doc/libs/1_55_0/libs/serialization/doc/tutorial.html#versioning
请注意如何序列化过程中的版本是由 BOOST_CLASS_VERSION
宏指定。
Note how the version during serialization is specified by the BOOST_CLASS_VERSION
macro.
下面是一个使用你的数据结构的以下版本概念证明:看到它的直播在Coliru
Here's a proof of concept using the following versions of your data struct: See it Live On Coliru
struct DataV0
{
float f = 3.14;
int i = 42;
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
if (0 != version)
throw std::runtime_error("Unsupported version");
ar & f;
ar & i;
}
};
现在,在你的V1的序列化格式,你已经改变了类型,在你的问题:
Now, in your V1 serialization format, you have changed the types as in your question:
struct DataV1
{
double d = 3.14;
size_t ul = 42;
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
switch(version)
{
case 0:
{
DataV0 old;
ar & old.f;
ar & old.i;
d = old.f;
assert(old.i >= std::numeric_limits<size_t>::min());
assert(old.i <= std::numeric_limits<size_t>::max());
ul = static_cast<size_t>(old.i);
}
break;
case 1:
ar & d;
ar & ul;
break;
}
}
};
BOOST_CLASS_VERSION(DataV1, 1)
一个完整的测试程序:
template <typename Data>
std::string to_string(Data d)
{
std::ostringstream oss;
boost::archive::text_oarchive oa(oss);
oa << d;
return oss.str();
}
template <typename Data>
bool verify(std::string const& text)
{
std::istringstream iss(text);
boost::archive::text_iarchive ia(iss);
Data d;
ia >> d;
return text == to_string(d);
}
int main()
{
std::string v0text = to_string(DataV0());
std::string v1text = to_string(DataV1());
std::cout << v0text << '\n';
std::cout << v1text << '\n';
std::cout << "v0 as v0: " << std::boolalpha << verify<DataV0>(v0text) << "\n";
std::cout << "v0 as v1: " << std::boolalpha << verify<DataV1>(v0text) << "\n";
std::cout << "v1 as v1: " << std::boolalpha << verify<DataV1>(v1text) << "\n";
try {
std::cout << "v1 as v0: " << std::boolalpha << verify<DataV0>(v1text) << "\n";
} catch (std::exception const& e)
{
std::cerr << "Threw the expected '" << e.what() << "'\n";
}
}
打印:
22 serialization::archive 10 0 0 3.1400001 42
22 serialization::archive 10 0 1 3.1400000000000001 42
v0 as v0: true
v0 as v1: false
v1 as v1: true
v1 as v0: Threw the expected 'Unsupported version'
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