The GNU C Library

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This is The GNU C Library Reference Manual, for Version 2.22 of the GNU C Library.

• Introduction:  Purpose of the GNU C Library.
• Error Reporting:  How library functions report errors.
• Memory:  Allocating virtual memory and controlling paging.
• Character Handling:  Character testing and conversion functions.
• String and Array Utilities:  Utilities for copying and comparing strings and arrays.
• Character Set Handling:  Support for extended character sets.
• Locales:  The country and language can affect the behavior of library functions.
• Message Translation:  How to make the program speak the user’s language.
• Searching and Sorting:  General searching and sorting functions.
• Pattern Matching:  Matching shell “globs” and regular expressions.
• I/O Overview:  Introduction to the I/O facilities.
• I/O on Streams:  High-level, portable I/O facilities.
• Low-Level I/O:  Low-level, less portable I/O.
• File System Interface:  Functions for manipulating files.
• Pipes and FIFOs:  A simple interprocess communication mechanism.
• Sockets:  A more complicated IPC mechanism, with networking support.
• Low-Level Terminal Interface:  How to change the characteristics of a terminal device.
• Syslog:  System logging and messaging.
• Mathematics:  Math functions, useful constants, random numbers.
• Arithmetic:  Low level arithmetic functions.
• Date and Time:  Functions for getting the date and time and formatting them nicely.
• Resource Usage And Limitation:  Functions for examining resource usage and getting and setting limits.
• Non-Local Exits:  Jumping out of nested function calls.
• Signal Handling:  How to send, block, and handle signals.
• Program Basics:  Writing the beginning and end of your program.
• Processes:  How to create processes and run other programs.
• Inter-Process Communication:  All about inter-process communication.
• Job Control:  All about process groups and sessions.
• Name Service Switch:  Accessing system databases.
• Users and Groups:  How users are identified and classified.
• System Management:  Controlling the system and getting information about it.
• System Configuration:  Parameters describing operating system limits.
• Cryptographic Functions:  DES encryption and password handling.
• Debugging Support:  Functions to help debugging applications.
• POSIX Threads:  POSIX Threads.
• Internal Probes:  Probes to monitor libc internal behavior. 
Appendices
• Language Features:  C language features provided by the library.
• Library Summary:  A summary showing the syntax, header file, and derivation of each library feature.
• Installation:  How to install the GNU C Library.
• Maintenance:  How to enhance and port the GNU C Library.
• Platform:  Describe all platform-specific facilities provided.
• Contributors:  Who wrote what parts of the GNU C Library.
• Free Manuals:  Free Software Needs Free Documentation.
• Copying:  The GNU Lesser General Public License says how you can copy and share the GNU C Library.
• Documentation License:  This manual is under the GNU Free Documentation License. 
Indices
• Concept Index:  Index of concepts and names.
• Type Index:  Index of types and type qualifiers.
• Function Index:  Index of functions and function-like macros.
• Variable Index:  Index of variables and variable-like macros.
• File Index:  Index of programs and files. 
 
 — The Detailed Node Listing —

Introduction
• Getting Started:  What this manual is for and how to use it.
• Standards and Portability:  Standards and sources upon which the GNU C library is based.
• Using the Library:  Some practical uses for the library.
• Roadmap to the Manual:  Overview of the remaining chapters in this manual. 
Standards and Portability
• ISO C:  The international standard for the C programming language.
• POSIX:  The ISO/IEC 9945 (aka IEEE 1003) standards for operating systems.
• Berkeley Unix:  BSD and SunOS.
• SVID:  The System V Interface Description.
• XPG:  The X/Open Portability Guide. 
POSIX
• POSIX Safety Concepts:  Safety concepts from POSIX.
• Unsafe Features:  Features that make functions unsafe.
• Conditionally Safe Features:  Features that make functions unsafe in the absence of workarounds.
• Other Safety Remarks:  Additional safety features and remarks. 
Using the Library
• Header Files:  How to include the header files in your programs.
• Macro Definitions:  Some functions in the library may really be implemented as macros.
• Reserved Names:  The C standard reserves some names for the library, and some for users.
• Feature Test Macros:  How to control what names are defined. 
Error Reporting
• Checking for Errors:  How errors are reported by library functions.
• Error Codes:  Error code macros; all of these expand into integer constant values.
• Error Messages:  Mapping error codes onto error messages. 
Memory
• Memory Concepts:  An introduction to concepts and terminology.
• Memory Allocation:  Allocating storage for your program data
• Resizing the Data Segment:  brk, sbrk
• Locking Pages:  Preventing page faults 
Memory Allocation
• Memory Allocation and C:  How to get different kinds of allocation in C.
• Unconstrained Allocation:  The malloc facility allows fully general dynamic allocation.
• Allocation Debugging:  Finding memory leaks and not freed memory.
• Obstacks:  Obstacks are less general than malloc but more efficient and convenient.
• Variable Size Automatic:  Allocation of variable-sized blocks of automatic storage that are freed when the calling function returns. 
Unconstrained Allocation
• Basic Allocation:  Simple use of malloc.
• Malloc Examples:  Examples of malloc. xmalloc.
• Freeing after Malloc:  Use free to free a block you got with malloc.
• Changing Block Size:  Use realloc to make a block bigger or smaller.
• Allocating Cleared Space:  Use calloc to allocate a block and clear it.
• Efficiency and Malloc:  Efficiency considerations in use of these functions.
• Aligned Memory Blocks:  Allocating specially aligned memory.
• Malloc Tunable Parameters:  Use mallopt to adjust allocation parameters.
• Heap Consistency Checking:  Automatic checking for errors.
• Hooks for Malloc:  You can use these hooks for debugging programs that use malloc.
• Statistics of Malloc:  Getting information about how much memory your program is using.
• Summary of Malloc:  Summary of malloc and related functions. 
Allocation Debugging
• Tracing malloc:  How to install the tracing functionality.
• Using the Memory Debugger:  Example programs excerpts.
• Tips for the Memory Debugger:  Some more or less clever ideas.
• Interpreting the traces:  What do all these lines mean? 
Obstacks
• Creating Obstacks:  How to declare an obstack in your program.
• Preparing for Obstacks:  Preparations needed before you can use obstacks.
• Allocation in an Obstack:  Allocating objects in an obstack.
• Freeing Obstack Objects:  Freeing objects in an obstack.
• Obstack Functions:  The obstack functions are both functions and macros.
• Growing Objects:  Making an object bigger by stages.
• Extra Fast Growing:  Extra-high-efficiency (though more complicated) growing objects.
• Status of an Obstack:  Inquiries about the status of an obstack.
• Obstacks Data Alignment:  Controlling alignment of objects in obstacks.
• Obstack Chunks:  How obstacks obtain and release chunks; efficiency considerations.
• Summary of Obstacks:   
Variable Size Automatic
• Alloca Example:  Example of using alloca.
• Advantages of Alloca:  Reasons to use alloca.
• Disadvantages of Alloca:  Reasons to avoid alloca.
• GNU C Variable-Size Arrays:  Only in GNU C, here is an alternative method of allocating dynamically and freeing automatically. 
Locking Pages
• Why Lock Pages:  Reasons to read this section.
• Locked Memory Details:  Everything you need to know locked memory
• Page Lock Functions:  Here’s how to do it. 
Character Handling
• Classification of Characters:  Testing whether characters are letters, digits, punctuation, etc. 
• Case Conversion:  Case mapping, and the like.



• Classification of Wide Characters:  Character class determination for
                                        wide characters.



• Using Wide Char Classes:  Notes on using the wide character
                                        classes.



• Wide Character Case Conversion:  Mapping of wide characters.



String and Array Utilities


• Representation of Strings:  Introduction to basic concepts.



• String/Array Conventions:  Whether to use a string function or an
				 arbitrary array function.



• String Length:  Determining the length of a string.



• Copying and Concatenation:  Functions to copy the contents of strings
				 and arrays.



• String/Array Comparison:  Functions for byte-wise and character-wise
				 comparison.



• Collation Functions:  Functions for collating strings.



• Search Functions:  Searching for a specific element or substring.



• Finding Tokens in a String:  Splitting a string into tokens by looking
				 for delimiters.



• strfry:  Function for flash-cooking a string.



• Trivial Encryption:  Obscuring data.



• Encode Binary Data:  Encoding and Decoding of Binary Data.



• Argz and Envz Vectors:  Null-separated string vectors.



Argz and Envz Vectors


• Argz Functions:  Operations on argz vectors.



• Envz Functions:  Additional operations on environment vectors.



Character Set Handling


• Extended Char Intro:  Introduction to Extended Characters.



• Charset Function Overview:  Overview about Character Handling
                                      Functions.



• Restartable multibyte conversion:  Restartable multibyte conversion
                                      Functions.



• Non-reentrant Conversion:  Non-reentrant Conversion Function.



• Generic Charset Conversion:  Generic Charset Conversion.



Restartable multibyte conversion


• Selecting the Conversion:  Selecting the conversion and its properties.



• Keeping the state:  Representing the state of the conversion.



• Converting a Character:  Converting Single Characters.



• Converting Strings:  Converting Multibyte and Wide Character
                                  Strings.



• Multibyte Conversion Example:  A Complete Multibyte Conversion Example.



Non-reentrant Conversion


• Non-reentrant Character Conversion:  Non-reentrant Conversion of Single
                                         Characters.



• Non-reentrant String Conversion:  Non-reentrant Conversion of Strings.



• Shift State:  States in Non-reentrant Functions.



Generic Charset Conversion


• Generic Conversion Interface:  Generic Character Set Conversion Interface.



• iconv Examples:  A complete iconv example.



• Other iconv Implementations:  Some Details about other iconv
                                     Implementations.



• glibc iconv Implementation:  The iconv Implementation in the GNU C
                                     library.



Locales


• Effects of Locale:  Actions affected by the choice of
                                 locale.



• Choosing Locale:  How the user specifies a locale.



• Locale Categories:  Different purposes for which you can
                                 select a locale.



• Setting the Locale:  How a program specifies the locale
                                 with library functions.



• Standard Locales:  Locale names available on all systems.



• Locale Names:  Format of system-specific locale names.



• Locale Information:  How to access the information for the locale.



• Formatting Numbers:  A dedicated function to format numbers.



• Yes-or-No Questions:  Check a Response against the locale.



Locale Information


• The Lame Way to Locale Data:  ISO C’s localeconv.



• The Elegant and Fast Way:  X/Open’s nl_langinfo.



The Lame Way to Locale Data


• General Numeric:  Parameters for formatting numbers and
                                 currency amounts.



• Currency Symbol:  How to print the symbol that identifies an
                                 amount of money (e.g. ‘$’).



• Sign of Money Amount:  How to print the (positive or negative) sign
                                 for a monetary amount, if one exists.



Message Translation


• Message catalogs a la X/Open:  The catgets family of functions.



• The Uniforum approach:  The gettext family of functions.



Message catalogs a la X/Open


• The catgets Functions:  The catgets function family.



• The message catalog files:  Format of the message catalog files.



• The gencat program:  How to generate message catalogs files which
                                can be used by the functions.



• Common Usage:  How to use the catgets interface.



The Uniforum approach


• Message catalogs with gettext:  The gettext family of functions.



• Helper programs for gettext:  Programs to handle message catalogs
                                    for gettext.



Message catalogs with gettext


• Translation with gettext:  What has to be done to translate a message.



• Locating gettext catalog:  How to determine which catalog to be used.



• Advanced gettext functions:  Additional functions for more complicated
                                    situations.



• Charset conversion in gettext:  How to specify the output character set
                                    gettext uses.



• GUI program problems:  How to use gettext in GUI programs.



• Using gettextized software:  The possibilities of the user to influence
                                    the way gettext works.



Searching and Sorting


• Comparison Functions:  Defining how to compare two objects.
				 Since the sort and search facilities
                                 are general, you have to specify the
                                 ordering.



• Array Search Function:  The bsearch function.



• Array Sort Function:  The qsort function.



• Search/Sort Example:  An example program.



• Hash Search Function:  The hsearch function.



• Tree Search Function:  The tsearch function.



Pattern Matching


• Wildcard Matching:  Matching a wildcard pattern against a single string.



• Globbing:  Finding the files that match a wildcard pattern.



• Regular Expressions:  Matching regular expressions against strings.



• Word Expansion:  Expanding shell variables, nested commands,
			    arithmetic, and wildcards.
			    This is what the shell does with shell commands.



Globbing


• Calling Glob:  Basic use of glob.



• Flags for Globbing:  Flags that enable various options in glob.



• More Flags for Globbing:  GNU specific extensions to glob.



Regular Expressions


• POSIX Regexp Compilation:  Using regcomp to prepare to match.



• Flags for POSIX Regexps:  Syntax variations for regcomp.



• Matching POSIX Regexps:  Using regexec to match the compiled
				   pattern that you get from regcomp.



• Regexp Subexpressions:  Finding which parts of the string were matched.



• Subexpression Complications:  Find points of which parts were matched.



• Regexp Cleanup:  Freeing storage; reporting errors.



Word Expansion


• Expansion Stages:  What word expansion does to a string.



• Calling Wordexp:  How to call wordexp.



• Flags for Wordexp:  Options you can enable in wordexp.



• Wordexp Example:  A sample program that does word expansion.



• Tilde Expansion:  Details of how tilde expansion works.



• Variable Substitution:  Different types of variable substitution.



I/O Overview


• I/O Concepts:  Some basic information and terminology.



• File Names:  How to refer to a file.



I/O Concepts


• Streams and File Descriptors:  The GNU C Library provides two ways
			             to access the contents of files.



• File Position:  The number of bytes from the
                                     beginning of the file.



File Names


• Directories:  Directories contain entries for files.



• File Name Resolution:  A file name specifies how to look up a file.



• File Name Errors:  Error conditions relating to file names.



• File Name Portability:  File name portability and syntax issues.



I/O on Streams


• Streams:  About the data type representing a stream.



• Standard Streams:  Streams to the standard input and output
				 devices are created for you.



• Opening Streams:  How to create a stream to talk to a file.



• Closing Streams:  Close a stream when you are finished with it.



• Streams and Threads:  Issues with streams in threaded programs.



• Streams and I18N:  Streams in internationalized applications.



• Simple Output:  Unformatted output by characters and lines.



• Character Input:  Unformatted input by characters and words.



• Line Input:  Reading a line or a record from a stream.



• Unreading:  Peeking ahead/pushing back input just read.



• Block Input/Output:  Input and output operations on blocks of data.



• Formatted Output:  printf and related functions.



• Customizing Printf:  You can define new conversion specifiers for
				 printf and friends.



• Formatted Input:  scanf and related functions.



• EOF and Errors:  How you can tell if an I/O error happens.



• Error Recovery:  What you can do about errors.



• Binary Streams:  Some systems distinguish between text files
				 and binary files.



• File Positioning:  About random-access streams.



• Portable Positioning:  Random access on peculiar ISO C systems.



• Stream Buffering:  How to control buffering of streams.



• Other Kinds of Streams:  Streams that do not necessarily correspond
				 to an open file.



• Formatted Messages:  Print strictly formatted messages.



Unreading


• Unreading Idea:  An explanation of unreading with pictures.



• How Unread:  How to call ungetc to do unreading.



Formatted Output


• Formatted Output Basics:  Some examples to get you started.



• Output Conversion Syntax:  General syntax of conversion
				 specifications.



• Table of Output Conversions:  Summary of output conversions and
				 what they do.



• Integer Conversions:  Details about formatting of integers.



• Floating-Point Conversions:  Details about formatting of
				 floating-point numbers.



• Other Output Conversions:  Details about formatting of strings,
				 characters, pointers, and the like.



• Formatted Output Functions:  Descriptions of the actual functions.



• Dynamic Output:  Functions that allocate memory for the output.



• Variable Arguments Output:  vprintf and friends.



• Parsing a Template String:  What kinds of args does a given template
				 call for?



• Example of Parsing:  Sample program using parse_printf_format.



Customizing Printf


• Registering New Conversions:  Using register_printf_function
					 to register a new output conversion.



• Conversion Specifier Options:  The handler must be able to get
					 the options specified in the
					 template when it is called.



• Defining the Output Handler:  Defining the handler and arginfo
					 functions that are passed as arguments
					 to register_printf_function.



• Printf Extension Example:  How to define a printf
					 handler function.



• Predefined Printf Handlers:  Predefined printf handlers.



Formatted Input


• Formatted Input Basics:  Some basics to get you started.



• Input Conversion Syntax:  Syntax of conversion specifications.



• Table of Input Conversions:  Summary of input conversions and what they do.



• Numeric Input Conversions:  Details of conversions for reading numbers.



• String Input Conversions:  Details of conversions for reading strings.



• Dynamic String Input:  String conversions that malloc the buffer.



• Other Input Conversions:  Details of miscellaneous other conversions.



• Formatted Input Functions:  Descriptions of the actual functions.



• Variable Arguments Input:  vscanf and friends.



Stream Buffering


• Buffering Concepts:  Terminology is defined here.



• Flushing Buffers:  How to ensure that output buffers are flushed.



• Controlling Buffering:  How to specify what kind of buffering to use.



Other Kinds of Streams


• String Streams:  Streams that get data from or put data in
				 a string or memory buffer.



• Custom Streams:  Defining your own streams with an arbitrary
				 input data source and/or output data sink.



Custom Streams


• Streams and Cookies:  The cookie records where to fetch or
				 store data that is read or written.



• Hook Functions:  How you should define the four hook
				 functions that a custom stream needs.



Formatted Messages


• Printing Formatted Messages:  The fmtmsg function.



• Adding Severity Classes:  Add more severity classes.



• Example:  How to use fmtmsg and addseverity.



Low-Level I/O


• Opening and Closing Files:  How to open and close file
                                         descriptors.



• I/O Primitives:  Reading and writing data.



• File Position Primitive:  Setting a descriptor’s file
                                         position.



• Descriptors and Streams:  Converting descriptor to stream
                                         or vice-versa.



• Stream/Descriptor Precautions:  Precautions needed if you use both
                                         descriptors and streams.



• Scatter-Gather:  Fast I/O to discontinuous buffers.



• Memory-mapped I/O:  Using files like memory.



• Waiting for I/O:  How to check for input or output
					 on multiple file descriptors.



• Synchronizing I/O:  Making sure all I/O actions completed.



• Asynchronous I/O:  Perform I/O in parallel.



• Control Operations:  Various other operations on file
					 descriptors.



• Duplicating Descriptors:  Fcntl commands for duplicating
                                         file descriptors.



• Descriptor Flags:  Fcntl commands for manipulating
                                         flags associated with file
                                         descriptors.



• File Status Flags:  Fcntl commands for manipulating
                                         flags associated with open files.



• File Locks:  Fcntl commands for implementing
                                         file locking.



• Open File Description Locks:  Fcntl commands for implementing
                                         open file description locking.



• Open File Description Locks Example:  An example of open file description lock
                                         usage



• Interrupt Input:  Getting an asynchronous signal when
                                         input arrives.



• IOCTLs:  Generic I/O Control operations.



Stream/Descriptor Precautions


• Linked Channels:  Dealing with channels sharing a file position.



• Independent Channels:  Dealing with separately opened, unlinked channels.



• Cleaning Streams:  Cleaning a stream makes it safe to use
                            another channel.



Asynchronous I/O


• Asynchronous Reads/Writes:  Asynchronous Read and Write Operations.



• Status of AIO Operations:  Getting the Status of AIO Operations.



• Synchronizing AIO Operations:  Getting into a consistent state.



• Cancel AIO Operations:  Cancellation of AIO Operations.



• Configuration of AIO:  How to optimize the AIO implementation.



File Status Flags


• Access Modes:  Whether the descriptor can read or write.



• Open-time Flags:  Details of open.



• Operating Modes:  Special modes to control I/O operations.



• Getting File Status Flags:  Fetching and changing these flags.



File System Interface


• Working Directory:  This is used to resolve relative
				 file names.



• Accessing Directories:  Finding out what files a directory
				 contains.



• Working with Directory Trees:  Apply actions to all files or a selectable
                                 subset of a directory hierarchy.



• Hard Links:  Adding alternate names to a file.



• Symbolic Links:  A file that “points to” a file name.



• Deleting Files:  How to delete a file, and what that means.



• Renaming Files:  Changing a file’s name.



• Creating Directories:  A system call just for creating a directory.



• File Attributes:  Attributes of individual files.



• Making Special Files:  How to create special files.



• Temporary Files:  Naming and creating temporary files.



Accessing Directories


• Directory Entries:  Format of one directory entry.



• Opening a Directory:  How to open a directory stream.



• Reading/Closing Directory:  How to read directory entries from the stream.



• Simple Directory Lister:  A very simple directory listing program.



• Random Access Directory:  Rereading part of the directory
                                 already read with the same stream.



• Scanning Directory Content:  Get entries for user selected subset of
                                 contents in given directory.



• Simple Directory Lister Mark II:  Revised version of the program.



File Attributes


• Attribute Meanings:  The names of the file attributes,
                                 and what their values mean.



• Reading Attributes:  How to read the attributes of a file.



• Testing File Type:  Distinguishing ordinary files,
                                 directories, links…



• File Owner:  How ownership for new files is determined,
			         and how to change it.



• Permission Bits:  How information about a file’s access
                                 mode is stored.



• Access Permission:  How the system decides who can access a file.



• Setting Permissions:  How permissions for new files are assigned,
			         and how to change them.



• Testing File Access:  How to find out if your process can
                                 access a file.



• File Times:  About the time attributes of a file.



• File Size:  Manually changing the size of a file.



• Storage Allocation:  Allocate backing storage for files.



Pipes and FIFOs


• Creating a Pipe:  Making a pipe with the pipe function.



• Pipe to a Subprocess:  Using a pipe to communicate with a
				 child process.



• FIFO Special Files:  Making a FIFO special file.



• Pipe Atomicity:  When pipe (or FIFO) I/O is atomic.



Sockets


• Socket Concepts:  Basic concepts you need to know about.



• Communication Styles:  Stream communication, datagrams and other styles.



• Socket Addresses:  How socket names (“addresses”) work.



• Interface Naming:  Identifying specific network interfaces.



• Local Namespace:  Details about the local namespace.



• Internet Namespace:  Details about the Internet namespace.



• Misc Namespaces:  Other namespaces not documented fully here.



• Open/Close Sockets:  Creating sockets and destroying them.



• Connections:  Operations on sockets with connection state.



• Datagrams:  Operations on datagram sockets.



• Inetd:  Inetd is a daemon that starts servers on request.
			   The most convenient way to write a server
			   is to make it work with Inetd.



• Socket Options:  Miscellaneous low-level socket options.



• Networks Database:  Accessing the database of network names.



Socket Addresses


• Address Formats:  About struct sockaddr.



• Setting Address:  Binding an address to a socket.



• Reading Address:  Reading the address of a socket.



Local Namespace


• Concepts:  What you need to understand.



• Details:  Address format, symbolic names, etc.



• Example:  Example of creating a socket.



Internet Namespace


• Internet Address Formats:  How socket addresses are specified in the
                                 Internet namespace.



• Host Addresses:  All about host addresses of Internet host.



• Ports:  Internet port numbers.



• Services Database:  Ports may have symbolic names.



• Byte Order:  Different hosts may use different byte
                                 ordering conventions; you need to
                                 canonicalize host address and port number.



• Protocols Database:  Referring to protocols by name.



• Inet Example:  Putting it all together.



Host Addresses


• Abstract Host Addresses:  What a host number consists of.



• Data type:  Data type for a host number.



• Functions:  Functions to operate on them.



• Names:  Translating host names to host numbers.



Open/Close Sockets


• Creating a Socket:  How to open a socket.



• Closing a Socket:  How to close a socket.



• Socket Pairs:  These are created like pipes.



Connections


• Connecting:  What the client program must do.



• Listening:  How a server program waits for requests.



• Accepting Connections:  What the server does when it gets a request.



• Who is Connected:  Getting the address of the
				other side of a connection.



• Transferring Data:  How to send and receive data.



• Byte Stream Example:  An example program: a client for communicating
			      over a byte stream socket in the Internet namespace.



• Server Example:  A corresponding server program.



• Out-of-Band Data:  This is an advanced feature.



Transferring Data


• Sending Data:  Sending data with send.



• Receiving Data:  Reading data with recv.



• Socket Data Options:  Using send and recv.



Datagrams


• Sending Datagrams:  Sending packets on a datagram socket.



• Receiving Datagrams:  Receiving packets on a datagram socket.



• Datagram Example:  An example program: packets sent over a
                           datagram socket in the local namespace.



• Example Receiver:  Another program, that receives those packets.



Inetd


• Inetd Servers:  



• Configuring Inetd:  



Socket Options


• Socket Option Functions:  The basic functions for setting and getting
                                 socket options.



• Socket-Level Options:  Details of the options at the socket level.



Low-Level Terminal Interface


• Is It a Terminal:  How to determine if a file is a terminal
			         device, and what its name is.



• I/O Queues:  About flow control and typeahead.



• Canonical or Not:  Two basic styles of input processing.



• Terminal Modes:  How to examine and modify flags controlling
			         details of terminal I/O: echoing,
                                 signals, editing.  Posix.



• BSD Terminal Modes:  BSD compatible terminal mode setting



• Line Control:  Sending break sequences, clearing
                                 terminal buffers …



• Noncanon Example:  How to read single characters without echo.



• Pseudo-Terminals:  How to open a pseudo-terminal.



Terminal Modes


• Mode Data Types:  The data type struct termios and
                                 related types.



• Mode Functions:  Functions to read and set the terminal
                                 attributes.



• Setting Modes:  The right way to set terminal attributes
                                 reliably.



• Input Modes:  Flags controlling low-level input handling.



• Output Modes:  Flags controlling low-level output handling.



• Control Modes:  Flags controlling serial port behavior.



• Local Modes:  Flags controlling high-level input handling.



• Line Speed:  How to read and set the terminal line speed.



• Special Characters:  Characters that have special effects,
			         and how to change them.



• Noncanonical Input:  Controlling how long to wait for input.



Special Characters


• Editing Characters:  Special characters that terminate lines and
                                  delete text, and other editing functions.



• Signal Characters:  Special characters that send or raise signals
                                  to or for certain classes of processes.



• Start/Stop Characters:  Special characters that suspend or resume
                                  suspended output.



• Other Special:  Other special characters for BSD systems:
				  they can discard output, and print status.



Pseudo-Terminals


• Allocation:  Allocating a pseudo terminal.



• Pseudo-Terminal Pairs:  How to open both sides of a
                            pseudo-terminal in a single operation.



Syslog


• Overview of Syslog:  Overview of a system’s Syslog facility



• Submitting Syslog Messages:  Functions to submit messages to Syslog



Submitting Syslog Messages


• openlog:  Open connection to Syslog



• syslog; vsyslog:  Submit message to Syslog



• closelog:  Close connection to Syslog



• setlogmask:  Cause certain messages to be ignored



• Syslog Example:  Example of all of the above



Mathematics


• Mathematical Constants:  Precise numeric values for often-used
                                 constants.



• Trig Functions:  Sine, cosine, tangent, and friends.



• Inverse Trig Functions:  Arcsine, arccosine, etc.



• Exponents and Logarithms:  Also pow and sqrt.



• Hyperbolic Functions:  sinh, cosh, tanh, etc.



• Special Functions:  Bessel, gamma, erf.



• Errors in Math Functions:  Known Maximum Errors in Math Functions.



• Pseudo-Random Numbers:  Functions for generating pseudo-random
				 numbers.



• FP Function Optimizations:  Fast code or small code.



Pseudo-Random Numbers


• ISO Random:  rand and friends.



• BSD Random:  random and friends.



• SVID Random:  drand48 and friends.



Arithmetic


• Integers:  Basic integer types and concepts



• Integer Division:  Integer division with guaranteed rounding.



• Floating Point Numbers:  Basic concepts.  IEEE 754.



• Floating Point Classes:  The five kinds of floating-point number.



• Floating Point Errors:  When something goes wrong in a calculation.



• Rounding:  Controlling how results are rounded.



• Control Functions:  Saving and restoring the FPU’s state.



• Arithmetic Functions:  Fundamental operations provided by the library.



• Complex Numbers:  The types.  Writing complex constants.



• Operations on Complex:  Projection, conjugation, decomposition.



• Parsing of Numbers:  Converting strings to numbers.



• System V Number Conversion:  An archaic way to convert numbers to strings.



Floating Point Errors


• FP Exceptions:  IEEE 754 math exceptions and how to detect them.



• Infinity and NaN:  Special values returned by calculations.



• Status bit operations:  Checking for exceptions after the fact.



• Math Error Reporting:  How the math functions report errors.



Arithmetic Functions


• Absolute Value:  Absolute values of integers and floats.



• Normalization Functions:  Extracting exponents and putting them back.



• Rounding Functions:  Rounding floats to integers.



• Remainder Functions:  Remainders on division, precisely defined.



• FP Bit Twiddling:  Sign bit adjustment.  Adding epsilon.



• FP Comparison Functions:  Comparisons without risk of exceptions.



• Misc FP Arithmetic:  Max, min, positive difference, multiply-add.



Parsing of Numbers


• Parsing of Integers:  Functions for conversion of integer values.



• Parsing of Floats:  Functions for conversion of floating-point
				 values.



Date and Time


• Time Basics:  Concepts and definitions.



• Elapsed Time:  Data types to represent elapsed times



• Processor And CPU Time:  Time a program has spent executing.



• Calendar Time:  Manipulation of “real” dates and times.



• Setting an Alarm:  Sending a signal after a specified time.



• Sleeping:  Waiting for a period of time.



Processor And CPU Time


• CPU Time:  The clock function.



• Processor Time:  The times function.



Calendar Time


• Simple Calendar Time:  Facilities for manipulating calendar time.



• High-Resolution Calendar:  A time representation with greater precision.



• Broken-down Time:  Facilities for manipulating local time.



• High Accuracy Clock:  Maintaining a high accuracy system clock.



• Formatting Calendar Time:  Converting times to strings.



• Parsing Date and Time:  Convert textual time and date information back
                                 into broken-down time values.



• TZ Variable:  How users specify the time zone.



• Time Zone Functions:  Functions to examine or specify the time zone.



• Time Functions Example:  An example program showing use of some of
				 the time functions.



Parsing Date and Time


• Low-Level Time String Parsing:  Interpret string according to given format.



• General Time String Parsing:  User-friendly function to parse data and
                                    time strings.



Resource Usage And Limitation


• Resource Usage:  Measuring various resources used.



• Limits on Resources:  Specifying limits on resource usage.



• Priority:  Reading or setting process run priority.



• Memory Resources:  Querying memory available resources.



• Processor Resources:  Learn about the processors available.



Priority


• Absolute Priority:  The first tier of priority.  Posix



• Realtime Scheduling:  Scheduling among the process nobility



• Basic Scheduling Functions:  Get/set scheduling policy, priority



• Traditional Scheduling:  Scheduling among the vulgar masses



• CPU Affinity:  Limiting execution to certain CPUs



Traditional Scheduling


• Traditional Scheduling Intro:  



• Traditional Scheduling Functions:  



Memory Resources


• Memory Subsystem:  Overview about traditional Unix memory handling.



• Query Memory Parameters:  How to get information about the memory
                                subsystem?



Non-Local Exits


• Intro:  When and how to use these facilities.



• Details:  Functions for non-local exits.



• Non-Local Exits and Signals:  Portability issues.



• System V contexts:  Complete context control a la System V.



Signal Handling


• Concepts of Signals:  Introduction to the signal facilities.



• Standard Signals:  Particular kinds of signals with
                                 standard names and meanings.



• Signal Actions:  Specifying what happens when a
                                 particular signal is delivered.



• Defining Handlers:  How to write a signal handler function.



• Interrupted Primitives:  Signal handlers affect use of open,
				 read, write and other functions.



• Generating Signals:  How to send a signal to a process.



• Blocking Signals:  Making the system hold signals temporarily.



• Waiting for a Signal:  Suspending your program until a signal
                                 arrives.



• Signal Stack:  Using a Separate Signal Stack.



• BSD Signal Handling:  Additional functions for backward
			         compatibility with BSD.



Concepts of Signals


• Kinds of Signals:  Some examples of what can cause a signal.



• Signal Generation:  Concepts of why and how signals occur.



• Delivery of Signal:  Concepts of what a signal does to the
                                 process.



Standard Signals


• Program Error Signals:  Used to report serious program errors.



• Termination Signals:  Used to interrupt and/or terminate the
                                 program.



• Alarm Signals:  Used to indicate expiration of timers.



• Asynchronous I/O Signals:  Used to indicate input is available.



• Job Control Signals:  Signals used to support job control.



• Operation Error Signals:  Used to report operational system errors.



• Miscellaneous Signals:  Miscellaneous Signals.



• Signal Messages:  Printing a message describing a signal.



Signal Actions


• Basic Signal Handling:  The simple signal function.



• Advanced Signal Handling:  The more powerful sigaction function.



• Signal and Sigaction:  How those two functions interact.



• Sigaction Function Example:  An example of using the sigaction function.



• Flags for Sigaction:  Specifying options for signal handling.



• Initial Signal Actions:  How programs inherit signal actions.



Defining Handlers


• Handler Returns:  Handlers that return normally, and what
                                 this means.



• Termination in Handler:  How handler functions terminate a program.



• Longjmp in Handler:  Nonlocal transfer of control out of a
                                 signal handler.



• Signals in Handler:  What happens when signals arrive while
                                 the handler is already occupied.



• Merged Signals:  When a second signal arrives before the
				 first is handled.



• Nonreentrancy:  Do not call any functions unless you know they
                                 are reentrant with respect to signals.



• Atomic Data Access:  A single handler can run in the middle of
                                 reading or writing a single object.



Atomic Data Access


• Non-atomic Example:  A program illustrating interrupted access.



• Types:  Data types that guarantee no interruption.



• Usage:  Proving that interruption is harmless.



Generating Signals


• Signaling Yourself:  A process can send a signal to itself.



• Signaling Another Process:  Send a signal to another process.



• Permission for kill:  Permission for using kill.



• Kill Example:  Using kill for Communication.



Blocking Signals


• Why Block:  The purpose of blocking signals.



• Signal Sets:  How to specify which signals to
                                         block.



• Process Signal Mask:  Blocking delivery of signals to your
				         process during normal execution.



• Testing for Delivery:  Blocking to Test for Delivery of
                                         a Signal.



• Blocking for Handler:  Blocking additional signals while a
				         handler is being run.



• Checking for Pending Signals:  Checking for Pending Signals



• Remembering a Signal:  How you can get almost the same
                                         effect as blocking a signal, by
                                         handling it and setting a flag
                                         to be tested later.



Waiting for a Signal


• Using Pause:  The simple way, using pause.



• Pause Problems:  Why the simple way is often not very good.



• Sigsuspend:  Reliably waiting for a specific signal.



Program Basics


• Program Arguments:  Parsing your program’s command-line arguments



• Environment Variables:  Less direct parameters affecting your program



• Auxiliary Vector:  Least direct parameters affecting your program



• System Calls:  Requesting service from the system



• Program Termination:  Telling the system you’re done; return status



Program Arguments


• Argument Syntax:  By convention, options start with a hyphen.



• Parsing Program Arguments:  Ways to parse program options and arguments.



Parsing Program Arguments


• Getopt:  Parsing program options using getopt.



• Argp:  Parsing program options using argp_parse.



• Suboptions:  Some programs need more detailed options.



• Suboptions Example:  This shows how it could be done for mount.



Environment Variables


• Environment Access:  How to get and set the values of
				 environment variables.



• Standard Environment:  These environment variables have
                		 standard interpretations.



Program Termination


• Normal Termination:  If a program calls exit, a
                                 process terminates normally.



• Exit Status:  The exit status provides information
                                 about why the process terminated.



• Cleanups on Exit:  A process can run its own cleanup
                                 functions upon normal termination.



• Aborting a Program:  The abort function causes
                                 abnormal program termination.



• Termination Internals:  What happens when a process terminates.



Processes


• Running a Command:  The easy way to run another program.



• Process Creation Concepts:  An overview of the hard way to do it.



• Process Identification:  How to get the process ID of a process.



• Creating a Process:  How to fork a child process.



• Executing a File:  How to make a process execute another program.



• Process Completion:  How to tell when a child process has completed.



• Process Completion Status:  How to interpret the status value
                                 returned from a child process.



• BSD Wait Functions:  More functions, for backward compatibility.



• Process Creation Example:  A complete example program.



Inter-Process Communication


• Semaphores:  Support for creating and managing semaphores



Job Control


• Concepts of Job Control:  Jobs can be controlled by a shell.



• Job Control is Optional:  Not all POSIX systems support job control.



• Controlling Terminal:  How a process gets its controlling terminal.



• Access to the Terminal:  How processes share the controlling terminal.



• Orphaned Process Groups:  Jobs left after the user logs out.



• Implementing a Shell:  What a shell must do to implement job control.



• Functions for Job Control:  Functions to control process groups.



Implementing a Shell


• Data Structures:  Introduction to the sample shell.



• Initializing the Shell:  What the shell must do to take
				 responsibility for job control.



• Launching Jobs:  Creating jobs to execute commands.



• Foreground and Background:  Putting a job in foreground of background.



• Stopped and Terminated Jobs:  Reporting job status.



• Continuing Stopped Jobs:  How to continue a stopped job in
				 the foreground or background.



• Missing Pieces:  Other parts of the shell.



Functions for Job Control


• Identifying the Terminal:  Determining the controlling terminal’s name.



• Process Group Functions:  Functions for manipulating process groups.



• Terminal Access Functions:  Functions for controlling terminal access.



Name Service Switch


• NSS Basics:  What is this NSS good for.



• NSS Configuration File:  Configuring NSS.



• NSS Module Internals:  How does it work internally.



• Extending NSS:  What to do to add services or databases.



NSS Configuration File


• Services in the NSS configuration:  Service names in the NSS configuration.



• Actions in the NSS configuration:  React appropriately to the lookup result.



• Notes on NSS Configuration File:  Things to take care about while
                                     configuring NSS.



NSS Module Internals


• NSS Module Names:  Construction of the interface function of
                                the NSS modules.



• NSS Modules Interface:  Programming interface in the NSS module
                                functions.



Extending NSS


• Adding another Service to NSS:  What is to do to add a new service.



• NSS Module Function Internals:  Guidelines for writing new NSS
                                        service functions.



Users and Groups


• User and Group IDs:  Each user has a unique numeric ID;
				 likewise for groups.



• Process Persona:  The user IDs and group IDs of a process.



• Why Change Persona:  Why a program might need to change
				 its user and/or group IDs.



• How Change Persona:  Changing the user and group IDs.



• Reading Persona:  How to examine the user and group IDs.



• Setting User ID:  Functions for setting the user ID.



• Setting Groups:  Functions for setting the group IDs.



• Enable/Disable Setuid:  Turning setuid access on and off.



• Setuid Program Example:  The pertinent parts of one sample program.



• Tips for Setuid:  How to avoid granting unlimited access.



• Who Logged In:  Getting the name of the user who logged in,
				 or of the real user ID of the current process.



• User Accounting Database:  Keeping information about users and various
                                 actions in databases.



• User Database:  Functions and data structures for
                        	 accessing the user database.



• Group Database:  Functions and data structures for
                        	 accessing the group database.



• Database Example:  Example program showing the use of database
				 inquiry functions.



• Netgroup Database:  Functions for accessing the netgroup database.



User Accounting Database


• Manipulating the Database:  Scanning and modifying the user
                                 accounting database.



• XPG Functions:  A standardized way for doing the same thing.



• Logging In and Out:  Functions from BSD that modify the user
                                 accounting database.



User Database


• User Data Structure:  What each user record contains.



• Lookup User:  How to look for a particular user.



• Scanning All Users:  Scanning the list of all users, one by one.



• Writing a User Entry:  How a program can rewrite a user’s record.



Group Database


• Group Data Structure:  What each group record contains.



• Lookup Group:  How to look for a particular group.



• Scanning All Groups:  Scanning the list of all groups.



Netgroup Database


• Netgroup Data:  Data in the Netgroup database and where
                                   it comes from.



• Lookup Netgroup:  How to look for a particular netgroup.



• Netgroup Membership:  How to test for netgroup membership.



System Management


• Host Identification:  Determining the name of the machine.



• Platform Type:  Determining operating system and basic
                                  machine type



• Filesystem Handling:  Controlling/querying mounts



• System Parameters:  Getting and setting various system parameters



Filesystem Handling


• Mount Information:  What is or could be mounted?



• Mount-Unmount-Remount:  Controlling what is mounted and how



Mount Information


• fstab:  The fstab file



• mtab:  The mtab file



• Other Mount Information:  Other (non-libc) sources of mount information



System Configuration


• General Limits:  Constants and functions that describe
				various process-related limits that have
				one uniform value for any given machine.



• System Options:  Optional POSIX features.



• Version Supported:  Version numbers of POSIX.1 and POSIX.2.



• Sysconf:  Getting specific configuration values
                                of general limits and system options.



• Minimums:  Minimum values for general limits.



• Limits for Files:  Size limitations that pertain to individual files.
                                These can vary between file systems
                                or even from file to file.



• Options for Files:  Optional features that some files may support.



• File Minimums:  Minimum values for file limits.



• Pathconf:  Getting the limit values for a particular file.



• Utility Limits:  Capacity limits of some POSIX.2 utility programs.



• Utility Minimums:  Minimum allowable values of those limits.



• String Parameters:  Getting the default search path.



Sysconf


• Sysconf Definition:  Detailed specifications of sysconf.



• Constants for Sysconf:  The list of parameters sysconf can read.



• Examples of Sysconf:  How to use sysconf and the parameter
				 macros properly together.



Cryptographic Functions


• Legal Problems:  This software can get you locked up, or worse.



• getpass:  Prompting the user for a password.



• crypt:  A one-way function for passwords.



• DES Encryption:  Routines for DES encryption.



Debugging Support


• Backtraces:  Obtaining and printing a back trace of the
                               current stack.



POSIX Threads


• Thread-specific Data:  Support for creating and
				  managing thread-specific data



• Non-POSIX Extensions:  Additional functions to extend
				  POSIX Thread functionality



Non-POSIX Extensions


• Default Thread Attributes:  Setting default attributes for
					  threads in a process.



Internal Probes


• Memory Allocation Probes:  Probes in the memory allocation subsystem



• Mathematical Function Probes:  Probes in mathematical functions



• Non-local Goto Probes:  Probes in setjmp and longjmp



Language Features


• Consistency Checking:  Using assert to abort if
				 something “impossible” happens.



• Variadic Functions:  Defining functions with varying numbers
                                 of args.



• Null Pointer Constant:  The macro NULL.



• Important Data Types:  Data types for object sizes.



• Data Type Measurements:  Parameters of data type representations.



Variadic Functions


• Why Variadic:  Reasons for making functions take
                                 variable arguments.



• How Variadic:  How to define and call variadic functions.



• Variadic Example:  A complete example.



How Variadic


• Variadic Prototypes:  How to make a prototype for a function
			  with variable arguments.



• Receiving Arguments:  Steps you must follow to access the
			  optional argument values.



• How Many Arguments:  How to decide whether there are more arguments.



• Calling Variadics:  Things you need to know about calling
			  variable arguments functions.



• Argument Macros:  Detailed specification of the macros
        		  for accessing variable arguments.



Data Type Measurements


• Width of Type:  How many bits does an integer type hold?



• Range of Type:  What are the largest and smallest values
			     that an integer type can hold?



• Floating Type Macros:  Parameters that measure the floating point types.



• Structure Measurement:  Getting measurements on structure types.



Floating Type Macros


• Floating Point Concepts:  Definitions of terminology.



• Floating Point Parameters:  Details of specific macros.



• IEEE Floating Point:  The measurements for one common
                                 representation.



Installation


• Configuring and compiling:  How to compile and test GNU libc.



• Running make install:  How to install it once you’ve got it
 compiled.



• Tools for Compilation:  You’ll need these first.



• Linux:  Specific advice for GNU/Linux systems.



• Reporting Bugs:  So they’ll get fixed.



Maintenance


• Source Layout:  How to add new functions or header files
                             to the GNU C Library.



• Porting:  How to port the GNU C Library to
                             a new machine or operating system.



Source Layout


• Platform:  Adding platform-specific
                                         features.



Porting


• Hierarchy Conventions:  The layout of the sysdeps hierarchy.



• Porting to Unix:  Porting the library to an average
                                   Unix-like system.



Platform


• PowerPC:  Facilities Specific to the PowerPC Architecture










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