C Language Support¶
C is a general-purpose low-level programming language that is widely used for writing code for embedded systems.
Zephyr is primarily written in C and natively supports applications written in
the C language. All Zephyr API functions and macros are implemented in C and
available as part of the C header files under the
include directory, so
writing Zephyr applications in C gives the developers access to the most
main() function must have the return type of
int as Zephyr
applications run in a “hosted” environment as defined by the C
standard. Applications must return zero (0) from main. All non-zero return
values are reserved.
Zephyr does not target a specific version of the C standards; however, the Zephyr codebase makes extensive use of the features newly introduced in the 1999 release of the ISO C standard (ISO/IEC 9899:1999, hereinafter referred to as C99) such as those listed below, effectively requiring the use of a compiler toolchain that supports the C99 standard and above:
standard boolean types (
fixed-width integer types (
Some Zephyr components make use of the features newly introduced in the 2011
release of the ISO C standard (ISO/IEC 9899:2011, hereinafter referred to as
C11) such as the type-generic expressions using the
_Generic keyword. For
cbprintf() component, used as the default formatted output
processor for Zephyr, makes use of the C11 type-generic expressions, and this
effectively requires most Zephyr applications to be compiled using a compiler
toolchain that supports the C11 standard and above.
In summary, it is recommended to use a compiler toolchain that supports at least the C11 standard for developing with Zephyr. It is, however, important to note that some optional Zephyr components and external modules may make use of the C language features that have been introduced in more recent versions of the standards, in which case it will be necessary to use a more up-to-date compiler toolchain that supports such standards.
The C Standard Library is an integral part of any C program, and Zephyr provides the support for a number of different C libraries for the applications to choose from, depending on the compiler toolchain being used to build the application.
C defines standard formatted output functions such as
sprintf and these functions are implemented by the C standard
Each C standard library has its own set of requirements and configurations for selecting the formatted output modes and capabilities. Refer to each C standard library documentation for more details.
Dynamic Memory Management¶
C defines a standard dynamic memory management interface (for example,
free()) and these functions are implemented by the
C standard libraries.
While the details of the dynamic memory management implementation varies across different C standard libraries, all supported libraries must conform to the following conventions. Every supported C standard library shall:
manage its own memory heap either internally or by invoking the hook functions (for example,
sbrk()) implemented in
maintain the architecture- and memory region-specific alignment requirements for the memory blocks allocated by the standard dynamic memory allocation interface (for example,
allocate memory blocks inside the
z_malloc_partitionmemory partition when userspace is enabled. See Pre-defined Memory Partitions.
For more details regarding the C standard library-specific memory management implementation, refer to each C standard library documentation.
C standard dynamic memory management interface functions such as
malloc() should be used only by the portable applications and
libraries that target multiple operating systems.