序列化map<fs::path，fs::path>？
序列化map<fs::path，fs::path>？
提问于 2021-04-28 07:38:57
我正在使用谷物库将我的类序列化为文件，但是在使用std::map时遇到了麻烦--特别是使用std::filesystem::path的地图。
假设我有一个Object类，它只包含一个map<fs::path, fs::path>，以及谷类所需的序列化函数：
struct Object
{
map<fs::path, fs::path> _map;
template<class Archive>
void serialize(Archive & archive)
{
archive(_map);
}
friend ostream& operator<<(ostream& outs, const Object c)
{
for (auto const &pair: c._map)
std::cout << "{" << pair.first << ": " << pair.second << "}\n";
return outs;
}
};在我的main函数中，我有：
int main()
{
// create Object
cout << "Creating object..." << endl;
Object o;
fs::path a = "bye.txt";
fs::path b = "hello.txt";
o._map[a] = b;
o._map[b] = a;
cout << "Object created: " << endl;
cout << o;
// serialize
cout << "Serializing object...." << endl;
stringstream ss;
cereal::BinaryOutputArchive oarchive(ss);
oarchive(o);
cout << "Object serialized." << endl;
// write to file
cout << "Writing serialized object to file...." << endl;
ofstream file("serialized_object");
file << ss.str();
file.close();
cout << "Object written to file." << endl;
// read from file
cout << "Reading from file..." << endl;
stringstream ss2;
fs::path ins = "serialized_object";
ifstream file_stream(ins, ios::binary);
ss2 << file_stream.rdbuf();
cereal::BinaryInputArchive iarchive(ss2);
Object out;
iarchive(out);
cout << "Object read from file." << endl;
cout << out;
}在我的输出中，我看到了从序列化文件中读取时出现的错误：
Creating object...
Object created:
{"bye.txt": "hello.txt"}
{"hello.txt": "bye.txt"}
Serializing object....
Object serialized.
Writing serialized object to file....
Object written to file.
Reading from file...
terminate called after throwing an instance of 'cereal::Exception'
what(): Failed to read 2573 bytes from input stream! Read 28我包含的内容包括：
#include <iostream>
#include <filesystem>
#include <fstream>
#include <string.h>
#include <map>
#include "cereal/types/map.hpp"
#include "cereal/archives/binary.hpp"
#include "cereal/types/string.hpp"为了能够序列化fs::path，我在开头包含了以下代码
namespace std
{
namespace filesystem
{
template<class Archive>
void CEREAL_LOAD_MINIMAL_FUNCTION_NAME(const Archive&, path& out, const string& in)
{
out = in;
}
template<class Archive>
string CEREAL_SAVE_MINIMAL_FUNCTION_NAME(const Archive& ar, const path& p)
{
return p.string();
}
}
}我确信我遗漏了一些明显的东西，因为这是我第一次使用谷类食品。有人知道我为什么会遇到这个问题吗？
回答 1
Stack Overflow用户
发布于 2021-05-08 00:01:26
根据cereal文档，在使用BinaryArchive时必须始终使用ios::binary标志。以下是其文档中this页面的特定部分：
当使用二进制存档和文件流(std::fstream)时，请记住在构造流时指定二进制标志(std::ios:: binary )。这可防止流将数据解释为ASCII字符并对其进行更改。
另一个问题是Cereal如何保证序列化已经完成。根据下面的link，在尝试读取存档之前，输出存档对象应该超出作用域(调用析构函数)。它们使用RAII方法，就像ifstream和here中提到的ofstream一样。
通过允许Cereal库在内部执行写入和读取操作，您可以极大地简化代码。以下是main函数的修改版本：
int main()
{
// create Object
cout << "Creating object..." << endl;
Object o;
fs::path a = "bye.txt";
fs::path b = "hello.txt";
o._map[a] = b;
o._map[b] = a;
cout << "Object created: " << endl;
cout << o;
cout << "Serializing object...." << endl;
// scope boundary (a function call would be cleaner)
{
ofstream ofstm("serialized_object", ios::binary);
cereal::BinaryOutputArchive oarchive(ofstm);
// serialize
oarchive(o);
}
cout << "Object serialized and written." << endl;
// deserialize the object by reading from the archive
Object out;
// scope boundary (a function would be cleaner)
{
ifstream istm("serialized_object", ios::binary);
cereal::BinaryInputArchive iarchive(istm);
//deserialize
iarchive(out);
}
cout << "Object read from file." << endl;
cout << out;
}我希望这能帮到你。请在使用前对其进行测试。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/67291931
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