To use system calls and library functions in a C program we simply call the appropriate C function (Appendix ).

We have already met some system calls when dealing with low level IO - `open(), creat(), read(), write() and close()` are examples.

Examples of standard library functions we have met include the higher level I/O
functions - `fopen(), fprintf()`, `sprintf()`, `malloc()` ...

All math functions such as `sin(), cos(), sqrt()` and random number
generators - `random(), seed(), lrand48(), drand48() etc.` are
standard math library functions.

NOTE: most standard library functions will use system calls within them.

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. These are available on line: Simply type `man` function name.

*e.g.* ~`man drand48`

would give information about this random number generator.

All system calls and library functions have been listed in a previous handout.

We have already seen examples of string handling library functions. For the rest of this course we will study the application of a few more system and library functions.

Fri May 20 13:40:49 BST 1994