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C++ Academy · Lesson

Constraints in Embedded No RTTI No Exceptions

Work within typical embedded subsets that disable RTTI and exceptions.

Constraints in Embedded No RTTI No Exceptions is a free C++ Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Embedded C++

Embedded systems have constraints: limited RAM, no MMU, real-time deadlines. The C++ "freestanding" subset removes parts of the language that are too expensive.

Why No RTTI?

RTTI (Run-Time Type Information) supports dynamic_cast and typeid. Each polymorphic class carries an extra pointer; RTTI tables consume code size. Disable with -fno-rtti.

Why No Exceptions?

Exceptions need stack unwinding tables and runtime support — code size and unpredictable timing. Many embedded codebases use -fno-exceptions.

g++ -fno-rtti -fno-exceptions main.cpp

Error Handling Without Exceptions

Use:

  • Return codes (std::expected, std::optional, error enums)
  • Out parameters for results
  • std::error_code for system errors

Result Types

C++23 std::expected<T, E> represents either a value or an error — like Rust s Result. Many embedded projects already use a custom Result type.

std::expected<int, ErrorCode> parse(const char* s);

if (auto r = parse("42"); r) use(*r);
else                       log_error(r.error());

Avoiding Dynamic Allocation

Heap fragmentation is a real-time killer. Embedded code often forbids new outside startup. Use:

  • Stack allocation
  • Static arrays
  • Memory pools
  • Embedded-friendly allocators

Static Memory Patterns

Reserve memory at compile or startup time.

template <typename T, size_t N>
class StaticVector {
    alignas(T) char storage_[sizeof(T) * N];
    size_t size_ = 0;
public:
    void push_back(const T& v);
    // ...
};

Compile-Time Polymorphism

Replace virtual functions with templates or CRTP when possible — no vtable, no indirect calls.

template <typename Derived>
class Base {
public:
    void process() { static_cast<Derived*>(this)->process_impl(); }
};

class Concrete : public Base<Concrete> {
public:
    void process_impl() { /* ... */ }
};

Freestanding Standard Library

The freestanding C++ subset excludes most of <iostream>, threading, and dynamic allocation. The standard explicitly defines what is available.

etl: Embedded Template Library

The Embedded Template Library (ETL) provides STL-like containers with deterministic size and no dynamic allocation.

Code Size Concerns

Use -Os for size optimization, -flto for link-time optimization, -ffunction-sections -fdata-sections -Wl,--gc-sections to drop unused code.

Real-World: Mars Rovers and Cars

C++ is widely used in safety-critical embedded systems — automotive (AUTOSAR), aerospace (MISRA), and medical (IEC 62304). Coding standards constrain the language further.

Quick Check

Which compiler flag disables exception support in C++ to reduce binary size?

Recap

Embedded C++ disables RTTI and exceptions for code size and predictability. Replace heap with static memory; use result types for errors; CRTP for polymorphism. Coding standards like MISRA further restrict the language.

Frequently asked questions

Is the “Constraints in Embedded No RTTI No Exceptions” lesson free?

Yes — the full text of “Constraints in Embedded No RTTI No Exceptions” is free to read here on the web, and the C++ Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C++ Academy course, upgrade to CoddyKit PRO.

What will I learn in “Constraints in Embedded No RTTI No Exceptions”?

Work within typical embedded subsets that disable RTTI and exceptions. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C++ Academy?

No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Constraints in Embedded No RTTI No Exceptions” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C++ Academy lesson?

Yes. Every C++ Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Constraints in Embedded No RTTI No Exceptions
  2. Memory Mapped IO and Volatile
  3. Real-Time Considerations and Latency
  4. Cross-Compilation for ARM Targets
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