Introduction

Last modified Tuesday, 15-Jul-2025 06:56:54 UTC.

C - Libraries not Language
- C is an extremely small language. Many of the functions of other languages are not included in C, e.g., no built in I/O, string handling or maths functions.
- C provides functionality through a rich set function libraries. For many practical purposes these may be regarded as being part of C
- A programmer can also develop his or her own function libraries and also include special purpose third party libraries, e.g., NAG, OpenGL.
- All libraries (except standard I/O) need to be explicitly linked in with the -l and, possibly, -L compiler options.
- Do Not Reinvent Wheels
  - It is wise for programmers to check whether a library function is available to perform a task before writing their own version. This will reduce program development time.
  - The library functions have been tested, so they are more likely to be correct than any function which the programmer might write. This will save time when debugging the program.
Finding information about library functions
- The UNIX manual has an entry for all available functions.
- Function documentation is stored in section 3 of the manual, and there are many other useful system calls in section 2. If you already know the name of the function you want, you can read the page by typing (to find about sqrt):
```
prompt> man 3 sqrt 
```
- If you don't know the name of the function, try man -k
```
prompt> man -k root 
```
- On any manual page, the SYNOPSIS section will include information on the use of the function. For example:
```
#include <time.h>

char *ctime(time_t *clock) 
```
  This means that you must have #include <time.h> in your file before you call ctime. And that function ctime takes a pointer to type time_t as an argument, and returns a string (char *). time_t will probably be defined in the same manual page.
- The DESCRIPTION section gives a short description of what the function does. For example:
```
ctime() converts a long integer, pointed to by clock,  to  a
26-character  string  of the form produced by asctime().  
```

Introduction

Exercises

Exam Style Questions