PlainOldData

Plain old data (POD) is a term used in C++ programming to describe simple data types that resemble C data structures in both memory layout and copying behavior. In modern C++ (since C++11), POD is defined as a type that is both trivially copyable and standard-layout.

Trivially copyable means that copying an object performs a trivial, bitwise copy and does not run any user-provided copy constructors, move constructors, destructors, or other custom code. Standard-layout ensures a predictable memory layout compatible with C structs, with a straightforward sequence of non-static data members and no complex features such as virtual functions or multiple inheritance in ways that would affect layout.

Practical implications of POD types include safe and efficient copying with memcpy, straightforward initialization, and easy interoperation with C interfaces and memory-mapped data. They typically serve as simple data containers, making serialization, deserialization, and binary I/O more straightforward. Common examples are plain structs that contain only primitive types or other POD members, such as struct Point { int x; int y; };.

POD types also impose limitations. They cannot have user-defined constructors or destructors, and they cannot rely on non-trivial initialization or behavior. Because the memory layout is intended to be predictable, relying on exact layouts across compilers or platforms can be risky due to padding and alignment differences. In addition, the term POD has evolved in C++ standards; modern descriptions prefer the terms trivially copyable and standard-layout to describe the same idea more precisely.

In sum, plain old data refers to simple, C-compatible aggregate types that are safely copyable and layout-predictable, making them useful for low-level programming tasks and interop scenarios.