Dies ist die Info-Datei libc.info, hergestellt von Makeinfo Version
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INFO-DIR-SECTION GNU libraries
START-INFO-DIR-ENTRY
* Libc: (libc).                 C library.
END-INFO-DIR-ENTRY

   This file documents the GNU C library.

   This is Edition 0.07 DRAFT, last updated 4 Oct 1996, of `The GNU C
Library Reference Manual', for Version 2.00 Beta.

   Copyright (C) 1993, '94, '95, '96, '97 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the section entitled "GNU Library General Public License" is
included exactly as in the original, and provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the text of the translation of the section
entitled "GNU Library General Public License" must be approved for
accuracy by the Foundation.


File: libc.info,  Node: Header Files,  Next: Macro Definitions,  Up: Using the Library

Header Files
------------

   Libraries for use by C programs really consist of two parts: "header
files" that define types and macros and declare variables and
functions; and the actual library or "archive" that contains the
definitions of the variables and functions.

   (Recall that in C, a "declaration" merely provides information that
a function or variable exists and gives its type.  For a function
declaration, information about the types of its arguments might be
provided as well.  The purpose of declarations is to allow the compiler
to correctly process references to the declared variables and functions.
A "definition", on the other hand, actually allocates storage for a
variable or says what a function does.)

   In order to use the facilities in the GNU C library, you should be
sure that your program source files include the appropriate header
files.  This is so that the compiler has declarations of these
facilities available and can correctly process references to them.
Once your program has been compiled, the linker resolves these
references to the actual definitions provided in the archive file.

   Header files are included into a program source file by the
`#include' preprocessor directive.  The C language supports two forms
of this directive; the first,

     #include "HEADER"

is typically used to include a header file HEADER that you write
yourself; this would contain definitions and declarations describing the
interfaces between the different parts of your particular application.
By contrast,

     #include <file.h>

is typically used to include a header file `file.h' that contains
definitions and declarations for a standard library.  This file would
normally be installed in a standard place by your system administrator.
You should use this second form for the C library header files.

   Typically, `#include' directives are placed at the top of the C
source file, before any other code.  If you begin your source files with
some comments explaining what the code in the file does (a good idea),
put the `#include' directives immediately afterwards, following the
feature test macro definition (*note Feature Test Macros::.).

   For more information about the use of header files and `#include'
directives, *note Header Files: (cpp.info)Header Files..

   The GNU C library provides several header files, each of which
contains the type and macro definitions and variable and function
declarations for a group of related facilities.  This means that your
programs may need to include several header files, depending on exactly
which facilities you are using.

   Some library header files include other library header files
automatically.  However, as a matter of programming style, you should
not rely on this; it is better to explicitly include all the header
files required for the library facilities you are using.  The GNU C
library header files have been written in such a way that it doesn't
matter if a header file is accidentally included more than once;
including a header file a second time has no effect.  Likewise, if your
program needs to include multiple header files, the order in which they
are included doesn't matter.

   *Compatibility Note:* Inclusion of standard header files in any
order and any number of times works in any ISO C implementation.
However, this has traditionally not been the case in many older C
implementations.

   Strictly speaking, you don't *have to* include a header file to use
a function it declares; you could declare the function explicitly
yourself, according to the specifications in this manual.  But it is
usually better to include the header file because it may define types
and macros that are not otherwise available and because it may define
more efficient macro replacements for some functions.  It is also a sure
way to have the correct declaration.


File: libc.info,  Node: Macro Definitions,  Next: Reserved Names,  Prev: Header Files,  Up: Using the Library

Macro Definitions of Functions
------------------------------

   If we describe something as a function in this manual, it may have a
macro definition as well.  This normally has no effect on how your
program runs--the macro definition does the same thing as the function
would.  In particular, macro equivalents for library functions evaluate
arguments exactly once, in the same way that a function call would.  The
main reason for these macro definitions is that sometimes they can
produce an inline expansion that is considerably faster than an actual
function call.

   Taking the address of a library function works even if it is also
defined as a macro.  This is because, in this context, the name of the
function isn't followed by the left parenthesis that is syntactically
necessary to recognize a macro call.

   You might occasionally want to avoid using the macro definition of a
function--perhaps to make your program easier to debug.  There are two
ways you can do this:

   * You can avoid a macro definition in a specific use by enclosing
     the name of the function in parentheses.  This works because the
     name of the function doesn't appear in a syntactic context where
     it is recognizable as a macro call.

   * You can suppress any macro definition for a whole source file by
     using the `#undef' preprocessor directive, unless otherwise stated
     explicitly in the description of that facility.

   For example, suppose the header file `stdlib.h' declares a function
named `abs' with

     extern int abs (int);

and also provides a macro definition for `abs'.  Then, in:

     #include <stdlib.h>
     int f (int *i) { return (abs (++*i)); }

the reference to `abs' might refer to either a macro or a function.  On
the other hand, in each of the following examples the reference is to a
function and not a macro.

     #include <stdlib.h>
     int g (int *i) { return ((abs)(++*i)); }
     
     #undef abs
     int h (int *i) { return (abs (++*i)); }

   Since macro definitions that double for a function behave in exactly
the same way as the actual function version, there is usually no need
for any of these methods.  In fact, removing macro definitions usually
just makes your program slower.


File: libc.info,  Node: Reserved Names,  Next: Feature Test Macros,  Prev: Macro Definitions,  Up: Using the Library

Reserved Names
--------------

   The names of all library types, macros, variables and functions that
come from the ISO C standard are reserved unconditionally; your program
*may not* redefine these names.  All other library names are reserved
if your program explicitly includes the header file that defines or
declares them.  There are several reasons for these restrictions:

   * Other people reading your code could get very confused if you were
     using a function named `exit' to do something completely different
     from what the standard `exit' function does, for example.
     Preventing this situation helps to make your programs easier to
     understand and contributes to modularity and maintainability.

   * It avoids the possibility of a user accidentally redefining a
     library function that is called by other library functions.  If
     redefinition were allowed, those other functions would not work
     properly.

   * It allows the compiler to do whatever special optimizations it
     pleases on calls to these functions, without the possibility that
     they may have been redefined by the user.  Some library
     facilities, such as those for dealing with variadic arguments
     (*note Variadic Functions::.)  and non-local exits (*note
     Non-Local Exits::.), actually require a considerable amount of
     cooperation on the part of the C compiler, and implementationally
     it might be easier for the compiler to treat these as built-in
     parts of the language.

   In addition to the names documented in this manual, reserved names
include all external identifiers (global functions and variables) that
begin with an underscore (`_') and all identifiers regardless of use
that begin with either two underscores or an underscore followed by a
capital letter are reserved names.  This is so that the library and
header files can define functions, variables, and macros for internal
purposes without risk of conflict with names in user programs.

   Some additional classes of identifier names are reserved for future
extensions to the C language or the POSIX.1 environment.  While using
these names for your own purposes right now might not cause a problem,
they do raise the possibility of conflict with future versions of the C
or POSIX standards, so you should avoid these names.

   * Names beginning with a capital `E' followed a digit or uppercase
     letter may be used for additional error code names.  *Note Error
     Reporting::.

   * Names that begin with either `is' or `to' followed by a lowercase
     letter may be used for additional character testing and conversion
     functions.  *Note Character Handling::.

   * Names that begin with `LC_' followed by an uppercase letter may be
     used for additional macros specifying locale attributes.  *Note
     Locales::.

   * Names of all existing mathematics functions (*note Mathematics::.)
     suffixed with `f' or `l' are reserved for corresponding functions
     that operate on `float' and `long double' arguments, respectively.

   * Names that begin with `SIG' followed by an uppercase letter are
     reserved for additional signal names.  *Note Standard Signals::.

   * Names that begin with `SIG_' followed by an uppercase letter are
     reserved for additional signal actions.  *Note Basic Signal
     Handling::.

   * Names beginning with `str', `mem', or `wcs' followed by a
     lowercase letter are reserved for additional string and array
     functions.  *Note String and Array Utilities::.

   * Names that end with `_t' are reserved for additional type names.

   In addition, some individual header files reserve names beyond those
that they actually define.  You only need to worry about these
restrictions if your program includes that particular header file.

   * The header file `dirent.h' reserves names prefixed with `d_'.

   * The header file `fcntl.h' reserves names prefixed with `l_', `F_',
     `O_', and `S_'.

   * The header file `grp.h' reserves names prefixed with `gr_'.

   * The header file `limits.h' reserves names suffixed with `_MAX'.

   * The header file `pwd.h' reserves names prefixed with `pw_'.

   * The header file `signal.h' reserves names prefixed with `sa_' and
     `SA_'.

   * The header file `sys/stat.h' reserves names prefixed with `st_'
     and `S_'.

   * The header file `sys/times.h' reserves names prefixed with `tms_'.

   * The header file `termios.h' reserves names prefixed with `c_',
     `V', `I', `O', and `TC'; and names prefixed with `B' followed by a
     digit.


File: libc.info,  Node: Feature Test Macros,  Prev: Reserved Names,  Up: Using the Library

Feature Test Macros
-------------------

   The exact set of features available when you compile a source file
is controlled by which "feature test macros" you define.

   If you compile your programs using `gcc -ansi', you get only the
ISO C library features, unless you explicitly request additional
features by defining one or more of the feature macros.  *Note GNU CC
Command Options: (gcc.info)Invoking GCC, for more information about GCC
options.

   You should define these macros by using `#define' preprocessor
directives at the top of your source code files.  These directives
*must* come before any `#include' of a system header file.  It is best
to make them the very first thing in the file, preceded only by
comments.  You could also use the `-D' option to GCC, but it's better
if you make the source files indicate their own meaning in a
self-contained way.

 - Macro: _POSIX_SOURCE
     If you define this macro, then the functionality from the POSIX.1
     standard (IEEE Standard 1003.1) is available, as well as all of the
     ISO C facilities.

 - Macro: _POSIX_C_SOURCE
     If you define this macro with a value of `1', then the
     functionality from the POSIX.1 standard (IEEE Standard 1003.1) is
     made available.  If you define this macro with a value of `2',
     then both the functionality from the POSIX.1 standard and the
     functionality from the POSIX.2 standard (IEEE Standard 1003.2) are
     made available.  This is in addition to the ISO C facilities.

 - Macro: _BSD_SOURCE
     If you define this macro, functionality derived from 4.3 BSD Unix
     is included as well as the ISO C, POSIX.1, and POSIX.2 material.

     Some of the features derived from 4.3 BSD Unix conflict with the
     corresponding features specified by the POSIX.1 standard.  If this
     macro is defined, the 4.3 BSD definitions take precedence over the
     POSIX definitions.

     Due to the nature of some of the conflicts between 4.3 BSD and
     POSIX.1, you need to use a special "BSD compatibility library"
     when linking programs compiled for BSD compatibility.  This is
     because some functions must be defined in two different ways, one
     of them in the normal C library, and one of them in the
     compatibility library.  If your program defines `_BSD_SOURCE', you
     must give the option `-lbsd-compat' to the compiler or linker when
     linking the program, to tell it to find functions in this special
     compatibility library before looking for them in the normal C
     library.

 - Macro: _SVID_SOURCE
     If you define this macro, functionality derived from SVID is
     included as well as the ISO C, POSIX.1, POSIX.2, and X/Open
     material.

 - Macro: _XOPEN_SOURCE
     If you define this macro, functionality described in the X/Open
     Portability Guide is included.  This is a superset of the POSIX.1
     and POSIX.2 functionality and in fact `_POSIX_SOURCE' and
     `_POSIX_C_SOURCE' are automatically defined.

     As the unification of all Unices, functionality only available in
     BSD and SVID is also included.

     If the macro `_XOPEN_SOURCE_EXTENDED' is also defined, even more
     functionality is available.  The extra functions will make all
     functions available which are necessary for the X/Open Unix brand.

 - Macro: _GNU_SOURCE
     If you define this macro, everything is included: ISO C, POSIX.1,
     POSIX.2, BSD, SVID, X/Open, and GNU extensions.  In the cases where
     POSIX.1 conflicts with BSD, the POSIX definitions take precedence.

     If you want to get the full effect of `_GNU_SOURCE' but make the
     BSD definitions take precedence over the POSIX definitions, use
     this sequence of definitions:

          #define _GNU_SOURCE
          #define _BSD_SOURCE
          #define _SVID_SOURCE

     Note that if you do this, you must link your program with the BSD
     compatibility library by passing the `-lbsd-compat' option to the
     compiler or linker.  *Note:* If you forget to do this, you may get
     very strange errors at run time.

 - Macro: _REENTRANT
 - Macro: _THREAD_SAFE
     If you define one of these macros, reentrant versions of several
     functions get declared.  Some of the functions are specified in
     POSIX.1c but many others are only available on a few other systems
     or are unique to GNU libc.  The problem is that the
     standardization of the thread safe C library interface still is
     behind.

     Unlike on some other systems no special version of the C library
     must be used for linking.  There is only one version but while
     compiling this it must have been specified to compile as thread
     safe.

   We recommend you use `_GNU_SOURCE' in new programs.  If you don't
specify the `-ansi' option to GCC and don't define any of these macros
explicitly, the effect is the same as defining `_POSIX_C_SOURCE' to 2
and `_POSIX_SOURCE', `_SVID_SOURCE', and `_BSD_SOURCE' to 1.

   When you define a feature test macro to request a larger class of
features, it is harmless to define in addition a feature test macro for
a subset of those features.  For example, if you define
`_POSIX_C_SOURCE', then defining `_POSIX_SOURCE' as well has no effect.
Likewise, if you define `_GNU_SOURCE', then defining either
`_POSIX_SOURCE' or `_POSIX_C_SOURCE' or `_SVID_SOURCE' as well has no
effect.

   Note, however, that the features of `_BSD_SOURCE' are not a subset of
any of the other feature test macros supported.  This is because it
defines BSD features that take precedence over the POSIX features that
are requested by the other macros.  For this reason, defining
`_BSD_SOURCE' in addition to the other feature test macros does have an
effect: it causes the BSD features to take priority over the conflicting
POSIX features.


File: libc.info,  Node: Roadmap to the Manual,  Prev: Using the Library,  Up: Introduction

Roadmap to the Manual
=====================

   Here is an overview of the contents of the remaining chapters of
this manual.

   * *Note Error Reporting::, describes how errors detected by the
     library are reported.

   * *Note Language Features::, contains information about library
     support for standard parts of the C language, including things
     like the `sizeof' operator and the symbolic constant `NULL', how
     to write functions accepting variable numbers of arguments, and
     constants describing the ranges and other properties of the
     numerical types.  There is also a simple debugging mechanism which
     allows you to put assertions in your code, and have diagnostic
     messages printed if the tests fail.

   * *Note Memory Allocation::, describes the GNU library's facilities
     for dynamic allocation of storage.  If you do not know in advance
     how much storage your program needs, you can allocate it
     dynamically instead, and manipulate it via pointers.

   * *Note Character Handling::, contains information about character
     classification functions (such as `isspace') and functions for
     performing case conversion.

   * *Note String and Array Utilities::, has descriptions of functions
     for manipulating strings (null-terminated character arrays) and
     general byte arrays, including operations such as copying and
     comparison.

   * *Note I/O Overview::, gives an overall look at the input and output
     facilities in the library, and contains information about basic
     concepts such as file names.

   * *Note I/O on Streams::, describes I/O operations involving streams
     (or `FILE *' objects).  These are the normal C library functions
     from `stdio.h'.

   * *Note Low-Level I/O::, contains information about I/O operations
     on file descriptors.  File descriptors are a lower-level mechanism
     specific to the Unix family of operating systems.

   * *Note File System Interface::, has descriptions of operations on
     entire files, such as functions for deleting and renaming them and
     for creating new directories.  This chapter also contains
     information about how you can access the attributes of a file,
     such as its owner and file protection modes.

   * *Note Pipes and FIFOs::, contains information about simple
     interprocess communication mechanisms.  Pipes allow communication
     between two related processes (such as between a parent and
     child), while FIFOs allow communication between processes sharing
     a common file system on the same machine.

   * *Note Sockets::, describes a more complicated interprocess
     communication mechanism that allows processes running on different
     machines to communicate over a network.  This chapter also
     contains information about Internet host addressing and how to use
     the system network databases.

   * *Note Low-Level Terminal Interface::, describes how you can change
     the attributes of a terminal device.  If you want to disable echo
     of characters typed by the user, for example, read this chapter.

   * *Note Mathematics::, contains information about the math library
     functions.  These include things like random-number generators and
     remainder functions on integers as well as the usual trigonometric
     and exponential functions on floating-point numbers.

   * *Note Low-Level Arithmetic Functions: Arithmetic, describes
     functions for simple arithmetic, analysis of floating-point
     values, and reading numbers from strings.

   * *Note Searching and Sorting::, contains information about functions
     for searching and sorting arrays.  You can use these functions on
     any kind of array by providing an appropriate comparison function.

   * *Note Pattern Matching::, presents functions for matching regular
     expressions and shell file name patterns, and for expanding words
     as the shell does.

   * *Note Date and Time::, describes functions for measuring both
     calendar time and CPU time, as well as functions for setting
     alarms and timers.

   * *Note Extended Characters::, contains information about
     manipulating characters and strings using character sets larger
     than will fit in the usual `char' data type.

   * *Note Locales::, describes how selecting a particular country or
     language affects the behavior of the library.  For example, the
     locale affects collation sequences for strings and how monetary
     values are formatted.

   * *Note Non-Local Exits::, contains descriptions of the `setjmp' and
     `longjmp' functions.  These functions provide a facility for
     `goto'-like jumps which can jump from one function to another.

   * *Note Signal Handling::, tells you all about signals--what they
     are, how to establish a handler that is called when a particular
     kind of signal is delivered, and how to prevent signals from
     arriving during critical sections of your program.

   * *Note Process Startup::, tells how your programs can access their
     command-line arguments and environment variables.

   * *Note Processes::, contains information about how to start new
     processes and run programs.

   * *Note Job Control::, describes functions for manipulating process
     groups and the controlling terminal.  This material is probably
     only of interest if you are writing a shell or other program which
     handles job control specially.

   * *Note Name Service Switch::, describes the services which are
     available for looking up names in the system databases, how to
     determine which service is used for which database, and how these
     services are implemented so that contributors can design their own
     services.

   * *Note User Database::, and *Note Group Database::, tell you how to
     access the system user and group databases.

   * *Note System Information::, describes functions for getting
     information about the hardware and software configuration your
     program is executing under.

   * *Note System Configuration::, tells you how you can get
     information about various operating system limits.  Most of these
     parameters are provided for compatibility with POSIX.

   * *Note Library Summary::, gives a summary of all the functions,
     variables, and macros in the library, with complete data types and
     function prototypes, and says what standard or system each is
     derived from.

   * *Note Maintenance::, explains how to build and install the GNU C
     library on your system, how to report any bugs you might find, and
     how to add new functions or port the library to a new system.

   If you already know the name of the facility you are interested in,
you can look it up in *Note Library Summary::.  This gives you a
summary of its syntax and a pointer to where you can find a more
detailed description.  This appendix is particularly useful if you just
want to verify the order and type of arguments to a function, for
example.  It also tells you what standard or system each function,
variable, or macro is derived from.


File: libc.info,  Node: Error Reporting,  Next: Memory Allocation,  Prev: Introduction,  Up: Top

Error Reporting
***************

   Many functions in the GNU C library detect and report error
conditions, and sometimes your programs need to check for these error
conditions.  For example, when you open an input file, you should
verify that the file was actually opened correctly, and print an error
message or take other appropriate action if the call to the library
function failed.

   This chapter describes how the error reporting facility works.  Your
program should include the header file `errno.h' to use this facility.

* Menü:

* 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.


File: libc.info,  Node: Checking for Errors,  Next: Error Codes,  Up: Error Reporting

Checking for Errors
===================

   Most library functions return a special value to indicate that they
have failed.  The special value is typically `-1', a null pointer, or a
constant such as `EOF' that is defined for that purpose.  But this
return value tells you only that an error has occurred.  To find out
what kind of error it was, you need to look at the error code stored in
the variable `errno'.  This variable is declared in the header file
`errno.h'.

 - Variable: volatile int errno
     The variable `errno' contains the system error number.  You can
     change the value of `errno'.

     Since `errno' is declared `volatile', it might be changed
     asynchronously by a signal handler; see *Note Defining Handlers::.
     However, a properly written signal handler saves and restores the
     value of `errno', so you generally do not need to worry about this
     possibility except when writing signal handlers.

     The initial value of `errno' at program startup is zero.  Many
     library functions are guaranteed to set it to certain nonzero
     values when they encounter certain kinds of errors.  These error
     conditions are listed for each function.  These functions do not
     change `errno' when they succeed; thus, the value of `errno' after
     a successful call is not necessarily zero, and you should not use
     `errno' to determine *whether* a call failed.  The proper way to
     do that is documented for each function.  *If* the call the
     failed, you can examine `errno'.

     Many library functions can set `errno' to a nonzero value as a
     result of calling other library functions which might fail.  You
     should assume that any library function might alter `errno' when
     the function returns an error.

     *Portability Note:* ISO C specifies `errno' as a "modifiable
     lvalue" rather than as a variable, permitting it to be implemented
     as a macro.  For example, its expansion might involve a function
     call, like `*_errno ()'.  In fact, that is what it is on the GNU
     system itself.  The GNU library, on non-GNU systems, does whatever
     is right for the particular system.

     There are a few library functions, like `sqrt' and `atan', that
     return a perfectly legitimate value in case of an error, but also
     set `errno'.  For these functions, if you want to check to see
     whether an error occurred, the recommended method is to set `errno'
     to zero before calling the function, and then check its value
     afterward.

   All the error codes have symbolic names; they are macros defined in
`errno.h'.  The names start with `E' and an upper-case letter or digit;
you should consider names of this form to be reserved names.  *Note
Reserved Names::.

   The error code values are all positive integers and are all distinct,
with one exception: `EWOULDBLOCK' and `EAGAIN' are the same.  Since the
values are distinct, you can use them as labels in a `switch'
statement; just don't use both `EWOULDBLOCK' and `EAGAIN'.  Your
program should not make any other assumptions about the specific values
of these symbolic constants.

   The value of `errno' doesn't necessarily have to correspond to any
of these macros, since some library functions might return other error
codes of their own for other situations.  The only values that are
guaranteed to be meaningful for a particular library function are the
ones that this manual lists for that function.

   On non-GNU systems, almost any system call can return `EFAULT' if it
is given an invalid pointer as an argument.  Since this could only
happen as a result of a bug in your program, and since it will not
happen on the GNU system, we have saved space by not mentioning
`EFAULT' in the descriptions of individual functions.

   In some Unix systems, many system calls can also return `EFAULT' if
given as an argument a pointer into the stack, and the kernel for some
obscure reason fails in its attempt to extend the stack.  If this ever
happens, you should probably try using statically or dynamically
allocated memory instead of stack memory on that system.


File: libc.info,  Node: Error Codes,  Next: Error Messages,  Prev: Checking for Errors,  Up: Error Reporting

Error Codes
===========

   The error code macros are defined in the header file `errno.h'.  All
of them expand into integer constant values.  Some of these error codes
can't occur on the GNU system, but they can occur using the GNU library
on other systems.

 - Macro: int EPERM
     Operation not permitted; only the owner of the file (or other
     resource) or processes with special privileges can perform the
     operation.

 - Macro: int ENOENT
     No such file or directory.  This is a "file doesn't exist" error
     for ordinary files that are referenced in contexts where they are
     expected to already exist.

 - Macro: int ESRCH
     No process matches the specified process ID.

 - Macro: int EINTR
     Interrupted function call; an asynchronous signal occurred and
     prevented completion of the call.  When this happens, you should
     try the call again.

     You can choose to have functions resume after a signal that is
     handled, rather than failing with `EINTR'; see *Note Interrupted
     Primitives::.

 - Macro: int EIO
     Input/output error; usually used for physical read or write errors.

 - Macro: int ENXIO
     No such device or address.  The system tried to use the device
     represented by a file you specified, and it couldn't find the
     device.  This can mean that the device file was installed
     incorrectly, or that the physical device is missing or not
     correctly attached to the computer.

 - Macro: int E2BIG
     Argument list too long; used when the arguments passed to a new
     program being executed with one of the `exec' functions (*note
     Executing a File::.) occupy too much memory space.  This condition
     never arises in the GNU system.

 - Macro: int ENOEXEC
     Invalid executable file format.  This condition is detected by the
     `exec' functions; see *Note Executing a File::.

 - Macro: int EBADF
     Bad file descriptor; for example, I/O on a descriptor that has been
     closed or reading from a descriptor open only for writing (or vice
     versa).

 - Macro: int ECHILD
     There are no child processes.  This error happens on operations
     that are supposed to manipulate child processes, when there aren't
     any processes to manipulate.

 - Macro: int EDEADLK
     Deadlock avoided; allocating a system resource would have resulted
     in a deadlock situation.  The system does not guarantee that it
     will notice all such situations.  This error means you got lucky
     and the system noticed; it might just hang.  *Note File Locks::,
     for an example.

 - Macro: int ENOMEM
     No memory available.  The system cannot allocate more virtual
     memory because its capacity is full.

 - Macro: int EACCES
     Permission denied; the file permissions do not allow the attempted
     operation.

 - Macro: int EFAULT
     Bad address; an invalid pointer was detected.  In the GNU system,
     this error never happens; you get a signal instead.

 - Macro: int ENOTBLK
     A file that isn't a block special file was given in a situation
     that requires one.  For example, trying to mount an ordinary file
     as a file system in Unix gives this error.

 - Macro: int EBUSY
     Resource busy; a system resource that can't be shared is already
     in use.  For example, if you try to delete a file that is the root
     of a currently mounted filesystem, you get this error.

 - Macro: int EEXIST
     File exists; an existing file was specified in a context where it
     only makes sense to specify a new file.

 - Macro: int EXDEV
     An attempt to make an improper link across file systems was
     detected.  This happens not only when you use `link' (*note Hard
     Links::.) but also when you rename a file with `rename' (*note
     Renaming Files::.).

 - Macro: int ENODEV
     The wrong type of device was given to a function that expects a
     particular sort of device.

 - Macro: int ENOTDIR
     A file that isn't a directory was specified when a directory is
     required.

 - Macro: int EISDIR
     File is a directory; you cannot open a directory for writing, or
     create or remove hard links to it.

 - Macro: int EINVAL
     Invalid argument.  This is used to indicate various kinds of
     problems with passing the wrong argument to a library function.

 - Macro: int EMFILE
     The current process has too many files open and can't open any
     more.  Duplicate descriptors do count toward this limit.

     In BSD and GNU, the number of open files is controlled by a
     resource limit that can usually be increased.  If you get this
     error, you might want to increase the `RLIMIT_NOFILE' limit or
     make it unlimited; *note Limits on Resources::..

 - Macro: int ENFILE
     There are too many distinct file openings in the entire system.
     Note that any number of linked channels count as just one file
     opening; see *Note Linked Channels::.  This error never occurs in
     the GNU system.

 - Macro: int ENOTTY
     Inappropriate I/O control operation, such as trying to set terminal
     modes on an ordinary file.

 - Macro: int ETXTBSY
     An attempt to execute a file that is currently open for writing, or
     write to a file that is currently being executed.  Often using a
     debugger to run a program is considered having it open for writing
     and will cause this error.  (The name stands for "text file
     busy".)  This is not an error in the GNU system; the text is
     copied as necessary.

 - Macro: int EFBIG
     File too big; the size of a file would be larger than allowed by
     the system.

 - Macro: int ENOSPC
     No space left on device; write operation on a file failed because
     the disk is full.

 - Macro: int ESPIPE
     Invalid seek operation (such as on a pipe).

 - Macro: int EROFS
     An attempt was made to modify something on a read-only file system.

 - Macro: int EMLINK
     Too many links; the link count of a single file would become too
     large.  `rename' can cause this error if the file being renamed
     already has as many links as it can take (*note Renaming Files::.).

 - Macro: int EPIPE
     Broken pipe; there is no process reading from the other end of a
     pipe.  Every library function that returns this error code also
     generates a `SIGPIPE' signal; this signal terminates the program
     if not handled or blocked.  Thus, your program will never actually
     see `EPIPE' unless it has handled or blocked `SIGPIPE'.

 - Macro: int EDOM
     Domain error; used by mathematical functions when an argument
     value does not fall into the domain over which the function is
     defined.

 - Macro: int ERANGE
     Range error; used by mathematical functions when the result value
     is not representable because of overflow or underflow.

 - Macro: int EAGAIN
     Resource temporarily unavailable; the call might work if you try
     again later.  The macro `EWOULDBLOCK' is another name for `EAGAIN';
     they are always the same in the GNU C library.

     This error can happen in a few different situations:

        * An operation that would block was attempted on an object that
          has non-blocking mode selected.  Trying the same operation
          again will block until some external condition makes it
          possible to read, write, or connect (whatever the operation).
          You can use `select' to find out when the operation will be
          possible; *note Waiting for I/O::..

          *Portability Note:* In many older Unix systems, this condition
          was indicated by `EWOULDBLOCK', which was a distinct error
          code different from `EAGAIN'.  To make your program portable,
          you should check for both codes and treat them the same.

        * A temporary resource shortage made an operation impossible.
          `fork' can return this error.  It indicates that the shortage
          is expected to pass, so your program can try the call again
          later and it may succeed.  It is probably a good idea to
          delay for a few seconds before trying it again, to allow time
          for other processes to release scarce resources.  Such
          shortages are usually fairly serious and affect the whole
          system, so usually an interactive program should report the
          error to the user and return to its command loop.

 - Macro: int EWOULDBLOCK
     In the GNU C library, this is another name for `EAGAIN' (above).
     The values are always the same, on every operating system.

     C libraries in many older Unix systems have `EWOULDBLOCK' as a
     separate error code.

 - Macro: int EINPROGRESS
     An operation that cannot complete immediately was initiated on an
     object that has non-blocking mode selected.  Some functions that
     must always block (such as `connect'; *note Connecting::.) never
     return `EAGAIN'.  Instead, they return `EINPROGRESS' to indicate
     that the operation has begun and will take some time.  Attempts to
     manipulate the object before the call completes return `EALREADY'.
     You can use the `select' function to find out when the pending
     operation has completed; *note Waiting for I/O::..

 - Macro: int EALREADY
     An operation is already in progress on an object that has
     non-blocking mode selected.

 - Macro: int ENOTSOCK
     A file that isn't a socket was specified when a socket is required.

 - Macro: int EMSGSIZE
     The size of a message sent on a socket was larger than the
     supported maximum size.

 - Macro: int EPROTOTYPE
     The socket type does not support the requested communications
     protocol.

 - Macro: int ENOPROTOOPT
     You specified a socket option that doesn't make sense for the
     particular protocol being used by the socket.  *Note Socket
     Options::.

 - Macro: int EPROTONOSUPPORT
     The socket domain does not support the requested communications
     protocol (perhaps because the requested protocol is completely
     invalid.)  *Note Creating a Socket::.

 - Macro: int ESOCKTNOSUPPORT
     The socket type is not supported.

 - Macro: int EOPNOTSUPP
     The operation you requested is not supported.  Some socket
     functions don't make sense for all types of sockets, and others
     may not be implemented for all communications protocols.  In the
     GNU system, this error can happen for many calls when the object
     does not support the particular operation; it is a generic
     indication that the server knows nothing to do for that call.

 - Macro: int EPFNOSUPPORT
     The socket communications protocol family you requested is not
     supported.

 - Macro: int EAFNOSUPPORT
     The address family specified for a socket is not supported; it is
     inconsistent with the protocol being used on the socket.  *Note
     Sockets::.

 - Macro: int EADDRINUSE
     The requested socket address is already in use.  *Note Socket
     Addresses::.

 - Macro: int EADDRNOTAVAIL
     The requested socket address is not available; for example, you
     tried to give a socket a name that doesn't match the local host
     name.  *Note Socket Addresses::.

 - Macro: int ENETDOWN
     A socket operation failed because the network was down.

 - Macro: int ENETUNREACH
     A socket operation failed because the subnet containing the remote
     host was unreachable.

 - Macro: int ENETRESET
     A network connection was reset because the remote host crashed.

 - Macro: int ECONNABORTED
     A network connection was aborted locally.

 - Macro: int ECONNRESET
     A network connection was closed for reasons outside the control of
     the local host, such as by the remote machine rebooting or an
     unrecoverable protocol violation.

 - Macro: int ENOBUFS
     The kernel's buffers for I/O operations are all in use.  In GNU,
     this error is always synonymous with `ENOMEM'; you may get one or
     the other from network operations.

 - Macro: int EISCONN
     You tried to connect a socket that is already connected.  *Note
     Connecting::.

 - Macro: int ENOTCONN
     The socket is not connected to anything.  You get this error when
     you try to transmit data over a socket, without first specifying a
     destination for the data.  For a connectionless socket (for
     datagram protocols, such as UDP), you get `EDESTADDRREQ' instead.

 - Macro: int EDESTADDRREQ
     No default destination address was set for the socket.  You get
     this error when you try to transmit data over a connectionless
     socket, without first specifying a destination for the data with
     `connect'.

 - Macro: int ESHUTDOWN
     The socket has already been shut down.

 - Macro: int ETOOMANYREFS
     ???

 - Macro: int ETIMEDOUT
     A socket operation with a specified timeout received no response
     during the timeout period.

 - Macro: int ECONNREFUSED
     A remote host refused to allow the network connection (typically
     because it is not running the requested service).

 - Macro: int ELOOP
     Too many levels of symbolic links were encountered in looking up a
     file name.  This often indicates a cycle of symbolic links.

 - Macro: int ENAMETOOLONG
     Filename too long (longer than `PATH_MAX'; *note Limits for
     Files::.) or host name too long (in `gethostname' or
     `sethostname'; *note Host Identification::.).

 - Macro: int EHOSTDOWN
     The remote host for a requested network connection is down.

 - Macro: int EHOSTUNREACH
     The remote host for a requested network connection is not
     reachable.

 - Macro: int ENOTEMPTY
     Directory not empty, where an empty directory was expected.
     Typically, this error occurs when you are trying to delete a
     directory.

 - Macro: int EPROCLIM
     This means that the per-user limit on new process would be
     exceeded by an attempted `fork'.  *Note Limits on Resources::, for
     details on the `RLIMIT_NPROC' limit.

 - Macro: int EUSERS
     The file quota system is confused because there are too many users.

 - Macro: int EDQUOT
     The user's disk quota was exceeded.

 - Macro: int ESTALE
     Stale NFS file handle.  This indicates an internal confusion in
     the NFS system which is due to file system rearrangements on the
     server host.  Repairing this condition usually requires unmounting
     and remounting the NFS file system on the local host.

 - Macro: int EREMOTE
     An attempt was made to NFS-mount a remote file system with a file
     name that already specifies an NFS-mounted file.  (This is an
     error on some operating systems, but we expect it to work properly
     on the GNU system, making this error code impossible.)

 - Macro: int EBADRPC
     ???

 - Macro: int ERPCMISMATCH
     ???

 - Macro: int EPROGUNAVAIL
     ???

 - Macro: int EPROGMISMATCH
     ???

 - Macro: int EPROCUNAVAIL
     ???

 - Macro: int ENOLCK
     No locks available.  This is used by the file locking facilities;
     see *Note File Locks::.  This error is never generated by the GNU
     system, but it can result from an operation to an NFS server
     running another operating system.

 - Macro: int EFTYPE
     Inappropriate file type or format.  The file was the wrong type
     for the operation, or a data file had the wrong format.

     On some systems `chmod' returns this error if you try to set the
     sticky bit on a non-directory file; *note Setting Permissions::..

 - Macro: int EAUTH
     ???

 - Macro: int ENEEDAUTH
     ???

 - Macro: int ENOSYS
     Function not implemented.  Some functions have commands or options
     defined that might not be supported in all implementations, and
     this is the kind of error you get if you request them and they are
     not supported.

 - Macro: int EILSEQ
     While decoding a multibyte character the function came along an
     invalid or an incomplete sequence of bytes or the given wide
     character is invalid.

 - Macro: int EBACKGROUND
     In the GNU system, servers supporting the `term' protocol return
     this error for certain operations when the caller is not in the
     foreground process group of the terminal.  Users do not usually
     see this error because functions such as `read' and `write'
     translate it into a `SIGTTIN' or `SIGTTOU' signal.  *Note Job
     Control::, for information on process groups and these signals.

 - Macro: int EDIED
     In the GNU system, opening a file returns this error when the file
     is translated by a program and the translator program dies while
     starting up, before it has connected to the file.

 - Macro: int ED
     The experienced user will know what is wrong.

 - Macro: int EGREGIOUS
     You did *what*?

 - Macro: int EIEIO
     Go home and have a glass of warm, dairy-fresh milk.

 - Macro: int EGRATUITOUS
     This error code has no purpose.

 - Macro: int EBADMSG

 - Macro: int EIDRM

 - Macro: int EMULTIHOP

 - Macro: int ENODATA

 - Macro: int ENOLINK

 - Macro: int ENOMSG

 - Macro: int ENOSR

 - Macro: int ENOSTR

 - Macro: int EOVERFLOW

 - Macro: int EPROTO

 - Macro: int ETIME

   *The following error codes are defined by the Linux/i386 kernel.
They are not yet documented.*

 - Macro: int ERESTART

 - Macro: int ECHRNG

 - Macro: int EL2NSYNC

 - Macro: int EL3HLT

 - Macro: int EL3RST

 - Macro: int ELNRNG

 - Macro: int EUNATCH

 - Macro: int ENOCSI

 - Macro: int EL2HLT

 - Macro: int EBADE

 - Macro: int EBADR

 - Macro: int EXFULL

 - Macro: int ENOANO

 - Macro: int EBADRQC

 - Macro: int EBADSLT

 - Macro: int EDEADLOCK

 - Macro: int EBFONT

 - Macro: int ENONET

 - Macro: int ENOPKG

 - Macro: int EADV

 - Macro: int ESRMNT

 - Macro: int ECOMM

 - Macro: int EDOTDOT

 - Macro: int ENOTUNIQ

 - Macro: int EBADFD

 - Macro: int EREMCHG

 - Macro: int ELIBACC

 - Macro: int ELIBBAD

 - Macro: int ELIBSCN

 - Macro: int ELIBMAX

 - Macro: int ELIBEXEC

 - Macro: int ESTRPIPE

 - Macro: int EUCLEAN

 - Macro: int ENOTNAM

 - Macro: int ENAVAIL

 - Macro: int EISNAM

 - Macro: int EREMOTEIO

 - Macro: int ENOMEDIUM

 - Macro: int EMEDIUMTYPE

