---
name: "intro"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/intro/3"
---

# intro(3)

introduction to the C libraries

## NAME

**intro** – introduction to the C libraries

## DESCRIPTION

This section provides an overview of the C library functions, their error returns and other common definitions and concepts. Most of these functions are available from the System library, *libSystem*. Other libraries must be indicated at compile time with the **-l** option of the compiler.

The various libraries (followed by the loader flag):

- libSystem (**-l***System*)

  Standard C library functions. When using the C compiler [cc(1)](/cc/1.md), it is not necessary to supply the loader flag **-l***System* for these functions. There are several \`libraries' or groups of functions included inside of libSystem: the standard I/O routines, database routines, bit operators, string operators, character tests and character operators, des encryption routines, storage allocation, time functions, signal handling and more.

  For compatibility with other systems, which provide these capabilities in separate libraries (such as libc), symbolic links are provided for **-l***c*, **-l***dbm*, **-l***dl*, **-l***info*, **-l***m*, **-l***poll*, **-l***pthread* and **-l***rpcsvc*; they all point to libSystem.

- libcurses (**-l***curses* **-l***termcap*)

  Terminal independent screen management routines for two dimensional non-bitmap display terminals. (See [ncurses(3)](/ncurses/3.md).)

- libl (**-l***l*)

  The library for [lex(1)](/lex/1.md).

- libtermcap (**-l***termcap*)

  The terminal independent operation library package. (See [termcap(3)](/termcap/3.md).)

- liby (**-l***y*)

  The library for [yacc(1)](/yacc/1.md).

## FILES

- */usr/lib/libSystem.dylib*

  the main System library

- */usr/lib/libSystem\_debug.dylib*

  the main System library compiled with debug support

- */usr/lib/libSystem\_profile.dylib*

  the main System library compiled for profiling

## SEE ALSO

[cc(1)](/cc/1.md), [ld(1)](/ld/1.md), [nm(1)](/nm/1.md), [intro(2)](/intro/2.md), [stdio(3)](/stdio/3.md)

## HISTORY

An **intro** manual appeared in Version 7 AT&T UNIX.