etl-fixed-containers

:::warning [UNTESTED] on real silicon Verified on native_sim only. ETL is header-only and portable; on-target the same #includes and API calls build and run unchanged. :::

Fixed-capacity containers with no heap and no STL, via the vendored Embedded Template Library (ETL 20.39.4).

Source: examples/peripheral-io/etl-fixed-containers/.

What it does

Builds two fixed-capacity containers and exercises them:

• etl::vector<int, 8> — push_back, size, capacity, and a range-for sum.
• etl::map<const char *, int, 4> — operator[] insert plus a find() lookup.

Capacity is part of the type, so all storage is inline — nothing reaches an allocator.

Why it matters on an MCU

The SDK builds M-class apps with no heap on the hot path and no exceptions. ETL is the direct answer to "I want std::vector semantics without std::vector's allocator":

• prj.conf deliberately does not set CONFIG_REQUIRES_FULL_LIBCPP, so the example builds in ETL_NO_STL mode.
• ETL_NO_EXCEPTIONS routes over-capacity through etl_error_handler rather than throwing.

ETL is header-only, so it has no Kconfig knob of its own — libraries: [etl] just puts the vendored headers and the SDK's etl_profile.h on the include path.

board.yaml

libraries:
  - name: etl
    cores: [m55_hp]

som:
  sku: E1M-AEN801

preset: e1m-evk
supported_boards:
  - e1m-evk
  - e1m-x-evk

cores:
  m55_hp:
    app: ./src
    peripherals: []

diagnostics:
  log_level: info

Pure logic — no peripherals, no chips.

Expected output

[etl-fixed-containers] vector: size=5 capacity=8
[etl-fixed-containers] vector: sum=15
[etl-fixed-containers] map: size=3
[etl-fixed-containers] map: lookup("b") = 2
[etl-fixed-containers] done

See also

• fmt-formatting — the other header-only C++ library example
• Examples overview