When creating a function for my embedded projects, I am often overwhelmed by the many possible ways to define methods or variables. Maybe this summary helps you as well!
Specifiers Overview
- inline: For small, often-used functions. Example: High-frequency sensor data processing functions.
- static: For shared class members or persistent local variables. Example: Counter in a function tracking the number of calls.
- constexpr: For compile-time constants. Example: Predefined configuration parameters like buffer sizes.
- volatile: For variables modified outside the program, such as by interrupts. Example: Flags set in an ISR (Interrupt Service Routine).
- register: Suggests storing a variable in a register. Example: Rarely specified, best left to compiler’s optimization.
- restrict: For performance optimization in pointer-intensive functions. Example: Signal processing functions using non-overlapping buffers.
- noexcept: For functions guaranteed not to throw exceptions. Example: Critical error handlers in embedded systems.
- [[noreturn]]: For functions that never return. Example: System reboot or fatal error handling functions.
- const: For immutable values and methods that do not modify the object. Example: Getters in classes representing device settings.
- mutable: For members modified in const member functions. Example: Cache variables in a const method.
- override: Ensures a member function overrides a virtual function in the base class. Example: Derived class methods that modify base class behavior.
- final: Prevents further derivation of classes or overriding of methods. Example: Critical base classes in a control system.
- explicit: Prevents implicit conversion by constructors. Example: Constructors that should not be called with a single argument implicitly.
- thread_local: For variables that are local to a thread. Example: Error state variable specific to each thread in a multithreaded application.
- [[nodiscard]]: Ensures function results are not ignored. Example: Functions returning error status that must always be checked.
- [[maybe_unused]]: Suppresses warnings for unused entities. Example: Parameters that are only used in debug builds.
- [[deprecated]]: Marks functions or entities as outdated. Example: Old API functions superseded by newer versions.
- [[likely]] and [[unlikely]]: Provides hints about branch prediction. Example: Conditions in performance-critical loops that are rarely true.
Practical Applications in Embedded Systems
- Prioritize consistent, predictable behaviors and execution times.
- Use
constexpr
andinline
to reduce runtime overhead. - Leverage
volatile
for hardware interaction to ensure real-time responsiveness. - Avoid dynamic memory allocation where possible; instead, use
static
storage duration. - Disable exceptions and use
noexcept
to clarify this intent. - Minimize use of
register
, instead relying on the compiler for register allocation.
Best Practices for Specifier Usage
- Use
const
andexplicit
to enforce immutability and prevent implicit behaviors. - Utilize
thread_local
for per-thread data to avoid costly synchronization in multi-threaded environments. - Mark critical functions with
[[nodiscard]]
to ensure that their results are handled correctly. - Employ
[[deprecated]]
to manage evolving firmware and API changes smoothly.
This has been summarized with the help of the almighty ChatGPT. For specific examples, take a look at the Roboost firmware, where I try to incorporate these practices.
So Long, and Thanks for All the Fish
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