errno.texi

一个C源代码分析器

@comment errno 62 @c DO NOT REMOVE
Too many levels of symbolic links were encountered in looking up a file name.
This often indicates a cycle of symbolic links.
@end deftypevr

@comment errno.h
@comment POSIX.1: File name too long
@deftypevr Macro int ENAMETOOLONG
@comment errno 63 @c DO NOT REMOVE
Filename too long (longer than @code{PATH_MAX}; @pxref{Limits for
Files}) or host name too long (in @code{gethostname} or
@code{sethostname}; @pxref{Host Identification}).
@end deftypevr

@comment errno.h
@comment BSD: Host is down
@deftypevr Macro int EHOSTDOWN
@comment errno 64 @c DO NOT REMOVE
The remote host for a requested network connection is down.
@end deftypevr

@comment errno.h
@comment BSD: No route to host
@deftypevr Macro int EHOSTUNREACH
@comment errno 65 @c DO NOT REMOVE
The remote host for a requested network connection is not reachable.
@end deftypevr

@comment errno.h
@comment POSIX.1: Directory not empty
@deftypevr Macro int ENOTEMPTY
@comment errno 66 @c DO NOT REMOVE
Directory not empty, where an empty directory was expected.  Typically,
this error occurs when you are trying to delete a directory.
@end deftypevr

@comment errno.h
@comment BSD: Too many processes
@deftypevr Macro int EPROCLIM
@comment errno 67 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment BSD: Too many users
@deftypevr Macro int EUSERS
@comment errno 68 @c DO NOT REMOVE
The file quota system is confused because there are too many users.
@c This can probably happen in a GNU system when using NFS.
@end deftypevr

@comment errno.h
@comment BSD: Disc quota exceeded
@deftypevr Macro int EDQUOT
@comment errno 69 @c DO NOT REMOVE
The user's disk quota was exceeded.
@end deftypevr

@comment errno.h
@comment BSD: Stale NFS file handle
@deftypevr Macro int ESTALE
@comment errno 70 @c DO NOT REMOVE
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.
@end deftypevr

@comment errno.h
@comment BSD: Too many levels of remote in path
@deftypevr Macro int EREMOTE
@comment errno 71 @c DO NOT REMOVE
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.)
@end deftypevr

@comment errno.h
@comment BSD: RPC struct is bad
@deftypevr Macro int EBADRPC
@comment errno 72 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment BSD: RPC version wrong
@deftypevr Macro int ERPCMISMATCH
@comment errno 73 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment BSD: RPC program not available
@deftypevr Macro int EPROGUNAVAIL
@comment errno 74 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment BSD: RPC program version wrong
@deftypevr Macro int EPROGMISMATCH
@comment errno 75 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment BSD: RPC bad procedure for program
@deftypevr Macro int EPROCUNAVAIL
@comment errno 76 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment POSIX.1: No locks available
@deftypevr Macro int ENOLCK
@comment errno 77 @c DO NOT REMOVE
No locks available.  This is used by the file locking facilities;
see @ref{File Locks}.
This error never occurs in the GNU system.
@end deftypevr

@comment errno.h
@comment BSD: Inappropriate file type or format
@deftypevr Macro int EFTYPE
@comment errno 79 @c DO NOT REMOVE
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 @code{chmod} returns this error if you try to set the
sticky bit on a non-directory file; @pxref{Setting Permissions}.
@end deftypevr

@comment errno.h
@comment BSD: Authentication error
@deftypevr Macro int EAUTH
@comment errno 80 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment BSD: Need authenticator
@deftypevr Macro int ENEEDAUTH
@comment errno 81 @c DO NOT REMOVE
???
@end deftypevr

@comment errno.h
@comment POSIX.1: Function not implemented
@deftypevr Macro int ENOSYS
@comment errno 78 @c DO NOT REMOVE
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.
@end deftypevr

@comment errno.h
@comment GNU: Inappropriate operation for background process
@deftypevr Macro int EBACKGROUND
@comment errno 100 @c DO NOT REMOVE
In the GNU system, servers supporting the @code{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 @code{read} and @code{write} translate
it into a @code{SIGTTIN} or @code{SIGTTOU} signal.  @xref{Job Control},
for information on process groups and these signals.
@end deftypevr

@comment errno.h
@comment GNU: Translator died
@deftypevr Macro int EDIED
@comment errno 101 @c DO NOT REMOVE
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.
@end deftypevr

@comment errno.h
@comment GNU: ?
@deftypevr Macro int ED
@comment errno 102 @c DO NOT REMOVE
The experienced user will know what is wrong.
@end deftypevr

@comment errno.h
@comment GNU: You really blew it this time
@deftypevr Macro int EGREGIOUS
@comment errno 103 @c DO NOT REMOVE
You did @strong{what}?
@end deftypevr

@comment errno.h
@comment GNU: Computer bought the farm
@deftypevr Macro int EIEIO
@comment errno 104 @c DO NOT REMOVE
Go home and have a glass of warm, dairy-fresh milk.
@end deftypevr

@comment errno.h
@comment GNU: Gratuitous error
@deftypevr Macro int EGRATUITOUS
@comment errno 105 @c DO NOT REMOVE
This error code has no purpose.
@end deftypevr


@node Error Messages,  , Error Codes, Error Reporting
@section Error Messages

The library has functions and variables designed to make it easy for
your program to report informative error messages in the customary
format about the failure of a library call.  The functions
@code{strerror} and @code{perror} give you the standard error message
for a given error code; the variable
@code{program_invocation_short_name} gives you convenient access to the
name of the program that encountered the error.

@comment string.h
@comment ANSI
@deftypefun {char *} strerror (int @var{errnum})
The @code{strerror} function maps the error code (@pxref{Checking for
Errors}) specified by the @var{errnum} argument to a descriptive error
message string.  The return value is a pointer to this string.

The value @var{errnum} normally comes from the variable @code{errno}.

You should not modify the string returned by @code{strerror}.  Also, if
you make subsequent calls to @code{strerror}, the string might be
overwritten.  (But it's guaranteed that no library function ever calls
@code{strerror} behind your back.)

The function @code{strerror} is declared in @file{string.h}.
@end deftypefun

@comment stdio.h
@comment ANSI
@deftypefun void perror (const char *@var{message})
This function prints an error message to the stream @code{stderr};
see @ref{Standard Streams}.

If you call @code{perror} with a @var{message} that is either a null
pointer or an empty string, @code{perror} just prints the error message 
corresponding to @code{errno}, adding a trailing newline.

If you supply a non-null @var{message} argument, then @code{perror}
prefixes its output with this string.  It adds a colon and a space 
character to separate the @var{message} from the error string corresponding
to @code{errno}.

The function @code{perror} is declared in @file{stdio.h}.
@end deftypefun

@code{strerror} and @code{perror} produce the exact same message for any
given error code; the precise text varies from system to system.  On the
GNU system, the messages are fairly short; there are no multi-line
messages or embedded newlines.  Each error message begins with a capital
letter and does not include any terminating punctuation.

@strong{Compatibility Note:}  The @code{strerror} function is a new
feature of ANSI C.  Many older C systems do not support this function
yet.

@cindex program name
@cindex name of running program
Many programs that don't read input from the terminal are designed to
exit if any system call fails.  By convention, the error message from
such a program should start with the program's name, sans directories.
You can find that name in the variable
@code{program_invocation_short_name}; the full file name is stored the
variable @code{program_invocation_name}:

@comment errno.h
@comment GNU
@deftypevar {char *} program_invocation_name 
This variable's value is the name that was used to invoke the program
running in the current process.  It is the same as @code{argv[0]}.  Note
that this is not necessarily a useful file name; often it contains no
directory names.  @xref{Program Arguments}.
@end deftypevar

@comment errno.h
@comment GNU
@deftypevar {char *} program_invocation_short_name 
This variable's value is the name that was used to invoke the program
running in the current process, with directory names removed.  (That is
to say, it is the same as @code{program_invocation_name} minus
everything up to the last slash, if any.)
@end deftypevar

The library initialization code sets up both of these variables before
calling @code{main}.

@strong{Portability Note:} These two variables are GNU extensions.  If
you want your program to work with non-GNU libraries, you must save the
value of @code{argv[0]} in @code{main}, and then strip off the directory
names yourself.  We added these extensions to make it possible to write
self-contained error-reporting subroutines that require no explicit
cooperation from @code{main}.

Here is an example showing how to handle failure to open a file
correctly.  The function @code{open_sesame} tries to open the named file
for reading and returns a stream if successful.  The @code{fopen}
library function returns a null pointer if it couldn't open the file for
some reason.  In that situation, @code{open_sesame} constructs an
appropriate error message using the @code{strerror} function, and
terminates the program.  If we were going to make some other library
calls before passing the error code to @code{strerror}, we'd have to
save it in a local variable instead, because those other library
functions might overwrite @code{errno} in the meantime.

@smallexample
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

FILE *
open_sesame (char *name)
@{ 
  FILE *stream;

  errno = 0;                     
  stream = fopen (name, "r");
  if (stream == NULL)
    @{
      fprintf (stderr, "%s: Couldn't open file %s; %s\n",
               program_invocation_short_name, name, strerror (errno));
      exit (EXIT_FAILURE);
    @}
  else
    return stream;
@}
@end smallexample