Attribute

Since C++11/C23, attributes allow compilers to add additional warning/error behaviours for variables, functions/methods, and objects. This can vary greatly from compiler-to-compiler — some are widely supported, but others are specific to a compiler (for example, MSVC has several unique attributes).

Attributes are stored in double square brackets, as followed:

[[ATTRIBUTE_NAME]]

A non-exhaustive list of the important attributes supported by most compilers:

• [[nodiscard]] (C++17, C23) — tags a function/method/type, and allows the compiler to issue a warning if a return value (from a function/method or any type).
  • Best practice is to use this extensively. Many non-mutating functions (accessors, const) should be tagged with nodiscard.
  • Since C++20, we can tag constructors. Since C++23, we can also tag lambdas.
• [[deprecated]] (C++14, C23) — marks a function as obsolete and discourages its use. This is intended for functions that are kept in an API to maintain backwards compatibility.