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42 lines
1.8 KiB
ReStructuredText
42 lines
1.8 KiB
ReStructuredText
C Support
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===========
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:link_to_translation:`zh_CN:[中文]`
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ESP-IDF is primarily written in C and provides C APIs. ESP-IDF can use one of the following C Standard Library implementations:
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- `Newlib <https://sourceware.org/newlib/>`_ (default)
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- `Picolibc <https://keithp.com/picolibc/>`_ (enabled with :ref:`CONFIG_LIBC_PICOLIBC<CONFIG_LIBC_PICOLIBC>` Kconfig option)
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The Newlib version is specified in :component_file:`newlib/sbom.yml`.
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In general, all C features supported by the compiler (currently GCC) can be used in ESP-IDF, unless otherwise noted in :ref:`unsupported_c_features` below.
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.. _c_version:
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C Version
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---------
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**GNU dialect of ISO C17** (``--std=gnu17``) is the current default C version in ESP-IDF.
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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:
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.. code-block:: cmake
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idf_component_register( ... )
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target_compile_options(${COMPONENT_LIB} PRIVATE -std=gnu11)
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If the public header files of the component also need to be compiled with the same language standard, replace the flag ``PRIVATE`` with ``PUBLIC``.
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.. _unsupported_c_features:
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Unsupported C Features
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----------------------
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The following features are not supported in ESP-IDF.
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Nested Function Pointers
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^^^^^^^^^^^^^^^^^^^^^^^^
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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.
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