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strerror---convert error number to string

Synopsis 
#include <string.h>
char *strerror(int errnum);
Description
strerror converts the error number errnum into a string. The value of errnum is usually a copy of errno. If errnum is not a known error number, the result points to an empty string.

This implementation of strerror prints out the following strings for each of the values defined in `errno.h':

E2BIG
Arg list too long
EACCES
Permission denied
EADV
Advertise error
EAGAIN
No more processes
EBADF
Bad file number
EBADMSG
Bad message
EBUSY
Device or resource busy
ECHILD
No children
ECOMM
Communication error
EDEADLK
Deadlock
EEXIST
File exists
EDOM
Math argument
EFAULT
Bad address
EFBIG
File too large
EIDRM
Identifier removed
EINTR
Interrupted system call
EINVAL
Invalid argument
EIO
I/O error
EISDIR
Is a directory
ELIBACC
Cannot access a needed shared library
ELIBBAD
Accessing a corrupted shared library
ELIBEXEC
Cannot exec a shared library directly
ELIBMAX
Attempting to link in more shared libraries than system limit
ELIBSCN
.lib section in a.out corrupted
EMFILE
Too many open files
EMLINK
Too many links
EMULTIHOP
Multihop attempted
ENFILE
File table overflow
ENODEV
No such device
ENOENT
No such file or directory
ENOEXEC
Exec format error
ENOLCK
No lock
ENOLINK
Virtual circuit is gone
ENOMEM
Not enough space
ENOMSG
No message of desired type
ENONET
Machine is not on the network
ENOPKG
No package
ENOSPC
No space left on device
ENOSR
No stream resources
ENOSTR
Not a stream
ENOTBLK
Block device required
ENOTDIR
Not a directory
ENOTTY
Not a character device
ENXIO
No such device or address
EPERM
Not owner
EPIPE
Broken pipe
EPROTO
Protocol error
ERANGE
Result too large
EREMOTE
Resource is remote
EROFS
Read-only file system
ESPIPE
Illegal seek
ESRCH
No such process
ESRMNT
Srmount error
ETIME
Stream ioctl timeout
ETXTBSY
Text file busy
EXDEV
Cross-device link


Returns
This function returns a pointer to a string. Your application must not modify that string.


Portability
ANSI C requires strerror, but does not specify the strings used for each error number.

Although this implementation of strerror is reentrant, ANSI C declares that subsequent calls to strerror may overwrite the result string; therefore portable code cannot depend on the reentrancy of this subroutine.

This implementation of strerror provides for user-defined extensibility. errno.h defines __ELASTERROR, which can be used as a base for user-defined error values. If the user supplies a routine named _user_strerror, and errnum passed to strerror does not match any of the supported values, _user_strerror is called with errnum as its argument.

_user_strerror takes one argument of type int, and returns a character pointer. If errnum is unknown to _user_strerror, _user_strerror returns NULL. The default _user_strerror returns NULL for all input values.

strerror requires no supporting OS subroutines.


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