AFAIK system call is how a program requests a service from an OS kernel (viz. it's an interface between user-level code and the kernel), but the call to the library function itself does not cause a switch to kernel mode.

Also, AFAIK usages of too many system calls normally may result into high number of CONTEXT SWITCHES so thought to ask before using any calls.


On Wed, Nov 6, 2013 at 7:23 PM, Igor R <boost.lists@gmail.com> wrote:
> Out of curiosity, wish to know if BOOST ASIO calls like -
>
> boost::asio::read()
> boost::asio::transfer_all()
> boost::asio::write()
>
> BOOST LEXICAL calls like -
> boost::lexical_cast<std::string>()
>
> BOOST POSIX TIME calls like -
> boost::posix_time::microsec_clock::universal_time()
> boost::posix_time::microsec_clock::ptime()
>
> are LIBRARY or SYSTEM calls.
>
> How to know which calls of BOOST are SYSTEM and LIBRARY calls?


Not sure what you mean by "system" and "library" (note that a Boost
function can rely on some CRT facility, which in turn might call OS
API), but you always can step into a desired function and see how it's
implemented.
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