Embedded Template Library (ETL)

Project documentation

Motivation

C++ is a great language to use for embedded applications and templates are a powerful aspect. The standard library can offer a great deal of well tested functionality, but there are some parts of the standard library that do not fit well with deterministic behaviour and limited resource requirements. These limitations usually preclude the use of dynamically allocated memory and containers with open ended sizes.

What is needed is a template library where the user can declare the size, or maximum size of any object upfront. Most embedded compilers do not currently support the standard beyond C++ 03, therefore excluding the programmer from using the enhanced features of the later library.

This is what the ETL attempts to achieve.

Summary

The ETL is not designed to completely replace the STL, but complement it. Its design objective covers three areas.

• Create a set of containers where the size or maximum size is determined at compile time. These containers are direct equivalents of those supplied in the STL.
• Be compatible with C++ 03 but implement as many of the C++ 11/14/17/20 additions as possible.
• Add other useful components that are not present in the standard library.

The embedded template library has been designed for lower resource embedded applications. It contains a set of containers, algorithms and utilities, some of which emulate parts of the STL. There is no dynamic memory allocation. The library makes no use of the heap. All of the containers have a fixed capacity allowing all memory allocation to be determined at compile time. The library is intended for any compiler that supports C++98/03/11/14/17/20.

Main features

• Cross platform. This library is not specific to any processor type.
• No dynamic memory allocation
• No RTTI required
• Very little use of virtual functions. They are used only when they are absolutely necessary for the required functionality
• A set of fixed capacity containers. (array, bitset, deque, forward_list, list, queue, stack, vector, map, set, etc.)
• As the storage for all of the container types is allocated as a contiguous block, they are extremely cache friendly
• Templated compile time constants
• Templated design pattern base classes (Visitor, Observer)
• Reverse engineered C++ 0x11 features (type traits, algorithms, containers etc.)
• Type-safe enumerations
• Type-safe typedefs
• 8, 16, 32 & 64 bit CRC calculations
• Checksums & hash functions
• Variants (a type that can store many types in a type-safe interface)
• Choice of asserts, exceptions, error handler or no checks on errors
• Unit tested (currently over 6480 tests), using VS2019, GCC 8.1.0, , GCC 9.3.0, Clang 9.0.0 & 10.0.0
• Many utilities for template support.
• Easy to read and documented source.
• Free support via email, GitHub and Slack

Any help porting the library to work under different platforms and compilers would be gratefully received. I am especially interested in people who are using Keil, IAR, Green Hills, TI Code Composer etc, bare metal or RTOS, and DSPs.

See (https://www.etlcpp.com) for up-to-date information.

Installing this library

You can find the setup steps here.

CMake

One way to use this library is to drop it somewhere in your project directory and then make the library available by using add_subdirectory

add_subdirectory(etl)
add_executable(foo main.cpp)
target_link_libraries(foo PRIVATE etl::etl)

If ETL library is used as a Git submodule it may require additional configuration for proper ETL version resolution by allowing the lookup for Git folder outside of the library root directory.

set(GIT_DIR_LOOKUP_POLICY ALLOW_LOOKING_ABOVE_CMAKE_SOURCE_DIR)
add_subdirectory(etl)

If you want to install this library with CMake, you can perform the following steps. On Linux, super user rights might be required to install the library, so it might be necessary to add sudo before the last command:

git clone https://github.com/ETLCPP/etl.git
cd etl
git checkout <targetVersion>
cmake -B build .
cmake --install build/

After the library has been installed, you can use find_package to use the library. Replace <majorVersionRequirement> with your desired major version:

find_package(etl <majorVersionRequirement>)
add_executable(foo main.cpp)
target_link_libraries(foo PRIVATE etl::etl)

Alternatively you can use FetchContent, replacing <targetVersion> with the version to install based on a git tag:

Include(FetchContent)

FetchContent_Declare(
  etl
  GIT_REPOSITORY https://github.com/ETLCPP/etl
  GIT_TAG        <targetVersion>
)

FetchContent_MakeAvailable(etl)

add_executable(foo main.cpp)
target_link_libraries(foo PRIVATE etl::etl)

Arduino library

The content of this repo is available as a library in the Arduino IDE (search for the "Embedded Template Library" in the IDE library manager). The Arduino library repository is available at https://github.com/ETLCPP/etl-arduino, see there for more details.