docs/en/api-guides/c.rst
:link_to_translation:zh_CN:[中文]
ESP-IDF is primarily written in C and provides C APIs. ESP-IDF can use one of the following C Standard Library implementations:
Newlib <https://sourceware.org/newlib/>_ (default)Picolibc <https://keithp.com/picolibc/>_ (enabled with :ref:CONFIG_LIBC_PICOLIBC<CONFIG_LIBC_PICOLIBC> Kconfig option)The Newlib version is specified in :component_file:esp_libc/sbom.yml.
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.
.. _c_version:
GNU dialect of ISO C23 (--std=gnu23) 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:
The following features are not supported in ESP-IDF.
Nested Function Pointers ^^^^^^^^^^^^^^^^^^^^^^^^
The GNU dialect of ISO C23 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.