esp-idf/docs/en/api-guides/c.rst
2024-04-25 11:01:13 +08:00

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C Support
===========
:link_to_translation:`zh_CN:[中文]`
ESP-IDF is primarily written in C and provides C APIs. ESP-IDF uses `Newlib <https://sourceware.org/newlib/>`_ as its C Standard Library implementation (the Newlib version is specified in :component_file:`newlib/sbom.yml`). In general, all C features that are supported by the compiler (currently GCC) can be used in ESP-IDF, unless specified in :ref:`unsupported_c_features` below.
.. _c_version:
C Version
---------
**GNU dialect of ISO C17** (``--std=gnu17``) is the current default C version in ESP-IDF.
To compile the source code of a certain component using a different language standard, set the desired compiler flag in the component's ``CMakeLists.txt`` file:
.. code-block:: cmake
idf_component_register( ... )
target_compile_options(${COMPONENT_LIB} PRIVATE -std=gnu11)
If the public header files of the component also need to be compiled with the same language standard, replace the flag ``PRIVATE`` with ``PUBLIC``.
.. _unsupported_c_features:
Unsupported C Features
----------------------
The following features are not supported in ESP-IDF.
Nested Function Pointers
^^^^^^^^^^^^^^^^^^^^^^^^
The **GNU dialect of ISO C17** supports `nested functions <https://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html>`_. However, ESP-IDF does not support referencing nested functions as pointers. This is due to the fact that the GCC compiler generates a `trampoline <https://gcc.gnu.org/onlinedocs/gccint/Trampolines.html>`_ (i.e., small piece of executable code) on the stack when a pointer to a nested function is referenced. ESP-IDF does not permit executing code from a stack, thus use of pointers to nested functions is not supported.