SO FAR, WE’VE PRESENTED A VARIETY OF FUNCTIONS that your program can invoke to perform system-related functions, such as parsing command-line options, manipulating processes, and mapping memory. If you look under the hood, you’ll find that these functions fall into two categories, based on how they are implemented.
• A library function is an ordinary function that resides in a library external to your program. Most of the library functions we’ve presented so far are in the standard C library,
libc. For example,
mkstemp are functions provided in the C library.
A call to a library function is just ...