Typically, in the world of embedded systems, every byte of memory and cycle of CPU time counts.  The reason for saying typically, is that, there are many different types of embedded system.  Some embedded systems require strict adherence to standards such as the MISRA standards.  Many other embedded applications require only loose adherence to such standards.  Either way the minimisation of memory usage and CPU cycles it important. 

C++ has often been regarded as unsuitable for embedded systems due to claims it is bloated, complex or unsuitable for resource constrained environments, like microcontrollers.  However, C++ is not just viable for embedded programming; it is a powerhouse which can deliver safer, more maintainable code without sacrificing performance.

The benefit which one is looking for, in switching from ‘C’ to C++ is that of abstraction, which improves code structure and safety, but without sacrificing performance or compiled code size.  This ‘magic’ is sometimes referred to as the “zero-cost abstraction principle”.  The idea is that you do not pay for what you do not use and what you do use is as efficient as hand-written low-level code.  This principle, championed by C++ creator Bjarne Stroustrup, makes C++ an ideal choice for embedded developers who want modern features without the overhead.

In this post, we'll explore what zero-cost abstractions mean, including highlighting key C++ features (including those of C++20), considering comparing code size to C and performance.

 

What Are Zero-Cost Abstractions?

Zero-cost abstractions allow you to write high-level, expressive code which compiles down to machine instructions as lean and fast as equivalent C. 

The principle boils down to two rules:

1)  You do not pay for what you do not use:  Features like exceptions or runtime type information (RTTI) can be disabled entirely, via compiler options.

2)  What you do use, you could not hand-code better:  Abstractions like templates or inline functions optimize away at compile time, leaving no runtime penalty.

In embedded systems, these are essential.  C++ can offer type safety, modularity, and reusability without extra cycles or byte (perfect for battery-powered IoT devices or real-time controllers).  Unlike ‘C’, where ‘generics’ often mean error-prone macros or void pointers; C++ lets you abstract without compromise.

Core C++ Abstractions That Shine in Embedded

C++ packs a toolkit of zero-cost features that elevate embedded code.  Here is a rundown:

Inline Functions: These expand at the point of call, eliminating function call overhead (similar to ‘C’ macros), but providing type-safety and capable of being debugged.

Scoped enum: Allows flexibility for defining named constants, but adds type safety and allows choice of size of representation.

Templates: Generic programming allows writing once for any type and the compiler generates specialized code.  Runtime polymorphism is not needed.  For sensor drivers, templates can handle different data types with zero overhead, avoiding ‘C’s manual duplication.

Constexpr: Compute at compile time!  From, simple constants to complex container operations, ‘constexpr’ shifts work off the MCU and embeds results directly in the binary.  For embedded code this is ideal for lookup tables or mathematics-heavy initialisation code.

Static Polymorphism: Resolve interfaces at compile time, with no need for virtual table lookup.  Ideal for device drivers where dynamic dispatch would waste cycles.

Move Semantics: Transfer resources efficiently without copies.

Smart Pointers:  Manages memory with RAII (Resource Acquisition Is Initialisation) to provide safety; with no leaks and no extra size in optimized builds.

Lambdas: Inline functions.  Lambdas inline like C callbacks but capture context safely.

 

The above items are not just nice to haves, but they prevent bugs which can plague ‘C’ code development, like, type mismatches or manual memory errors.  The important point, is that, the C++ code could match ‘C’s performance.

 

C++20 Newest Abstractions to Enhance Embedded

C++20 can take zero-cost abstraction to new heights, making embedded code even more expressive and safe:

Concepts: Constrain templates declaratively.  This can avoid the more cryptic SFINAE errors, by ensuring types meet requirements at compile time.  For embedded generics (e.g., numeric types only), this boosts type safety without the need for runtime checks.

Ranges Library: Pipeline data transformations lazily.  For example, filter and transform sensor data in one readable line, which then compiles to a single efficient loop.

Constexpr Enhancements:  Now with dynamic allocation!  Build and process vectors or strings at compile time, reducing runtime footprint.

<=> Operator: The spaceship operator allows auto-generation for consistent ordering.

std::span: Safe array views.  Span wraps pointers with sizes to prevent overflows.

 

These features are tools for writing robust embedded code which scales.

 

Does C++ Really Bloat Embedded Binaries?

A common perception is that C++ inflates code size.  How can all of this fancy encapsulated code not translate to additional binary code?  The reality is that with optimizations (enabling optimisations with the compiler and switching off exceptions and run-time type information), C++ often matches or possibly beats ‘C’.  Whilst templates might duplicate code, the linker could fold redundancies and constexpr allows embedding of data efficiently.

In principle, C++'s abstractions reduce overall size by avoiding ‘C’ duplication of manual code.  Online tools like Godbolt can help confirm the near assembly identical code (compared to ‘C’).

 

Why C++ Can Wins Over ‘C’ in Embedded

The ‘C’ language may be simple, but C++ adds value without cost:

Safety: RAII and types prevent leaks and errors that may crash embedded devices.

Maintainability: Abstractions scale for large teams; ‘C’s flat code does not.

Ecosystem: STL subsets (e.g., vector) are lightweight; no need to reinvent wheels.

There are many myths like "C++ is too big", but modern compilers strip the fat.  As embedded shifts to complex IoT, C++ has virtues which can enhance the coding experience.

 

Conclusion: Embrace C++ for Embedded Development

 

Zero-cost abstractions make C++ a joy for embedded systems, enabling performance like C, but safer and more productive.  Whether you're optimizing battery life or scaling firmware, features from templates to C++20 concepts empower you without penalties.  The principle is "What you do use, you could not hand code any better."