The text formats, like JSON or XML, are portable and self-descriptive, but serialization/deserialization needs additional data processing, and archive takes significantly more space than the binary one and in result might be slower to transmit if needed. Changing the sign of an integer and loading number that does not fit into a new type, e.g.
Additionally this library has support for shared pointers (only one copy of data pointed to is saved) and objects with multiple inheritance (also virtual inheritance).
Our newcereal_fwdlibrary addressed the forward compatibility problem for C++ serialization. To circumvent this problem,cereal_fwdadds ability to change fields type toOmittedFieldTag. streams formed using network sockets. Some initial assumptions and design decisions were challenged during implementation and are described below. In a worst case size of copied data may be close to the size of all data being read. Removing fields without addingOmittedFieldTagtrying to load more fields than were saved will result in exception. The user only has to mark object usingSerializableinterface and pass object instance to data stream, which uses runtime object reflection to determine objects contents and properly serialize them. This library makes reversible deconstruction of an arbitrary set of C++ data structures possible. The benchmark results are available at project web site. This functionality requires language-independent description of the data structure. Result of this method indicates if the field being read was really saved or ifOmittedFieldTagwas used in the archive. It can significantly reduce archive size when storing multiple items of the same type. Size of created executable was 30% bigger for ourcereal_fwdthan forcerealand comparable withBoost.Serialization. Such memory allocations may not be acceptable in some applications. Because of that, option to limit maximal size of helper buffer has been added. Renaming structures or classes; the exceptions, caused by storing fully qualified type name in the archive: Renamed class cannot be stored using shared pointer. Conclusions are included in Chapter 5. To date our community has made over 100 million downloads. In particular, C++ standard library contains stream representation as well as conversions between a binary or text streams and built-in data types. To achieve that serialization tool must introduce some portable object identifiers and reference tracing. If the object pointed by shared pointer from unknown field needs to be read by other pointers, instead of using main stream, data would be copied from temporary objects. Enumerations are saved as numeric values.Boost.Serializationsupports pointer and reference marshaling and demarshaling, i.e. Although C++ is usually supported by cross-language solutions, like Apache Thrift or Google Protocol Buffers, it lacks its own in-language serialization support , like Java, C# or Python.
Thanks to additional abstraction layer provided by Java virtual machine (JVM), serialization procedures do not need to be concerned with execution environment architecturememory model, including endianness and object representation, is fixed by virtual machine. Various platforms can have distinct memory alignments, which in turn can make the same object occupy different amounts of bytes on other systems. In the first version of the application, only one pointer toCclass object is saved. Another rejected solution was partial interpretation of data and storing it in temporary objects of basic types supported by archive. Some languages or libraries (C#, Java, C++ Qt) force default encoding of character string in memory (usually from UTF  encoding family); others (C, C++) rely on platform or user settings. Even putting endianness issues aside and focusing on objects composed of only basic types (without pointers or references), this approach just cannot work in a portable way, due to differences in how an object is represented in memory. For example, consider removing fieldquestion arises how older software will interpret missing data, which it still expects. Here, a List of String objects is serialized and then deserialized. To add the serialization for user type, the programmer should implement methodserialize, where one of its argument is archive and the second is the version number. there's always a need to pay attention to exceptions; in particular, it always needs to be called, or else resources will leak, it will automatically flush the stream, if necessary, closing a stream a second time has no consequence.
For every other occurrence of the same object, only numerical identifier of previously saved data is stored. This leaves some changes in the data structure layout to be still forward incompatible. The issue becomes even more difficult in case of recursive object connections, depicted in Figure 5. Our team is growing all the time, so were always on the lookout for smart people who want to help us reshape the world of scientific publishing. Newcereal_fwdlibrary was based oncerealas it already provides some of the required features, and thanks to relying on C++11 language features, it has much simpler implementation than popularBoost.Serialization. In the first version of application, two shared pointersOuter::qandQ::zare saved. //The behavior of the logger can be configured through a. Users that want to add serialization to existing code base, with already defined C++ classes, are usually left withBoost.Serialization(as part of the most popularBoostlibrary), whose binary archives are not portable. C and C++ use the platform-dependent definition ofintit has to be at least 16-bit, usually 32-bit on modern architectures, but can be anything bigger. ::stringand other containers. Identifier for specific class is saved only once in stream, for the first occurrence of given type, accompanied with corresponding ordinal number. C++ runtime type information is not portable) and use it to choose proper marshaling and unmarshalling procedures. Inheritance becomes more troublesome when multiple inheritance is allowed, like in C++, in contrast to languages that permit only multiple interfaces (C#, Java). Potentially a more portable but possible less-efficient way is based on variable-length integer encoding, as described in the next section as solution for strings and array length encoding.
Renamed class cannot be saved using pointer to the base class.
::size_torlongdirectly, without additional size information, may produce data which may not be readable on other platforms. Developers can use some of cross-language tools, like Apache Thrift or Protocol Buffers, but those enforce data types used in application. This approach would introduce computational overhead even if no other pointer to the same object was saved. That solves some problems with portability of the archive between various real machines. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. Unsigned integer numbers variable-length encoded.
Adding new fields at the end of the objects serialization code; new fields have to be loaded conditionally using class version stored in archive. When data saved by the second version is read by the first one, data needed byOuter::qfield can be found inInner::qposition. Yet out-of-the-box availability and simplicity of use make such solution a good option for the homogeneous systems. The authors declare that they have no competing interests. It is a low-level technique, and several technical issues should be considered like endianness, size of memory representation, representation of numbers, object references, recursive object connections and others. A proper complete serialization should follow all references used in the object. Using IDL-based serialization is not always an option for C++ project, as it can be less efficient or too limited than language-specific solution. Apart from adding new fields, at some point of application evolution, it might be justified to remove no longer needed fields. One of the solutions to the described problem is saving stream position of each occurrence of shared pointers and restoring it in case data is needed to read the object by other pointers. Supporting possibility for adding fields in newer versions of application should be straightforwardold version of application should just ignore unknown fields. The perfect solution, meeting all requirements, does not exist, because the requirements are contradictory: The fastest serialization/deserialization process is achieved for binary format, but it is not portable between platforms. Serializationor marshalingis the process of converting object state into a format that can be transmitted or stored. Due to built-in forward compatibility support, there is also a smaller chance that change in the IDL would need to propagate to all involved parties than previous solutions. /** The stream of bytes is mostly memory- and time-efficient; therefore the serialized buffer is the smallest and usually fastest to marshall and deserialize; however the buffer is unreadable to developers and most susceptible for portability issues. Minimize allocations during saving and loading process. Binary formats are more implementation-dependent and are not so standardized. In the second version, pointers are saved in the following order:Inner::z,Inner::q,Q::z,Outer::q,Q::z. If the first occurrence of shared pointer is saved by field which is present only in the new version and the older version used for reading, reading such shared pointer may be difficult. How? For pointers of unknown type,nullptrvalue is set, and reading process is continued without interruption.
Virtual diamond inheritance object serialization. Some common solutions include number size as part of serialized data or user forced to explicitly state size of data during serialization and deserialization, for example, by using a method namedwriteInt16or by using types like C++sstd.::uint64_t. The most compact is also binary format (without included data description), but such archive is hard to use to exchange information between modules written in different programming languages. Another approach is to use tagged fields, which also help with forward compatibility, as described below. Some languages, like C++, give the user partial control over the objects memory layout, but even those features would not help in creating fully portable object representation. An example of such situation is depicted in Figure 11. For loading process similar mapping between identifiers and shared pointers is maintained. Protocol Buffers had the smallest code size for serializing numbers, but in the case of collections, code size was the biggest. The library is publicly accessible at under BSD-like licence. Performance and memory consumption of newly createdcereal_fwdwas compared against originalcereal,Boost.Serialization, as similar library, and Protocol Buffers as popular non-C++-dedicated solution.
This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Two incompatible formats are in common use to represent larger than 1 byte numerical values when stored into memory: a big-endian, where the most significant byte (i.e. it's almost always a good idea to use buffering (default size is 8K), it's often possible to use abstract base class references, instead of references to concrete classes. Then serialization could just flatten such structure, serializing referenced objects as parts of holder objects. NETBinaryFormatter and Pythonpickle. Support portability between different platforms. Archive mediumis a name for file or stream. It too makes developer responsible for writing explicit marshaling procedures and supports only backward compatibility. If, additionally, the older version of software is able to read data saved by newer version, the serialization mechanism has forward compatibility. Additionally various languages differently define their basic integer type. Figure 10 shows how structure can be serialized using selected archive type. This requires access to complete class inheritance hierarchy and runtime type information. It is implemented by most of platforms used today. Identifier can be any string; by default fully qualified name of the type is used.