... Using UNIX System Calls and Library Functions . ... To use system calls and library functions in a C program we simply call the appropriate C function. Examples of standard library functions we have met include the higher level I/O functions -- fprintf() , malloc() .. ... For most system calls and library functions we have to include an appropriate header file. e.g. stdio.h, math.h . ... Information on nearly all system calls and library functions is available in manual pages. ...