the difference between posix user and c user

Sebastian Huber sebastian.huber at
Fri Jan 12 06:05:40 UTC 2018

On 12/01/18 02:28, Russell Haley wrote:
> On Wed, Jan 10, 2018 at 8:50 AM, Gedare Bloom<gedare at>  wrote:
>> On Thu, Dec 28, 2017 at 9:35 PM, at
>> < at>  wrote:
>>> is the posix api and the c api used together?
>> POSIX and ISO-C tend to go together.
>> With RTEMS, you can also use ISO-C with the "Classic API", which
>> consists of interface functions accessible from C programs as
>> described in the "C User Guide".
>>> sorry . i am also confused about this two things . because i find that when
>>> i config the rtems kernel ,there is a option which is  --enable posix.
>> Most new development and ports of existing software probably use POSIX
>> anyway, except for the simplest applications. This configure option
>> was provided historically as a way to avoid compiling the POSIX
>> library into an application, but modern compilers are able to remove
>> the unused code any way.
> I really liked the cleanliness of the "Classic API". Are there
> limitations to it? Is there an advantage to the POSIX API other than
> compatibility? (I just threw up a little in my mouth)
> Is the Classic API going to be fully supported going forward?

We removed already some Classic API functions in RTEMS 4.11 and 5. See 
the "Deprecated and Removed Directives" section in the manual, e.g.

I guess the remaining Classic API will only change if we start to 
support quantum computers.

Sebastian Huber, embedded brains GmbH

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