errno

ERRNO(3)		      Library functions			     ERRNO(3)



NAME
       errno - number of last error

SYNOPSIS
       #include <errno.h>

       extern int errno;

DESCRIPTION
       The  integer errno is set by system calls (and some library functions)
       to indicate what went wrong.  Its value is significant only  when  the
       call  returned an error (usually -1), and a library function that does
       succeed is allowed to change errno.

       Sometimes, when -1 is also a legal return value one has to zero	errno
       before the call in order to detect possible errors.

       errno  is  defined  by the ISO C standard to be a modifiable lvalue of
       type int, and must not be explicitly declared; errno may be  a  macro.
       errno  is  thread-local;	 setting it in one thread does not affect its
       value in any other thread.

       Valid error numbers are all non-zero; errno is never set	 to  zero  by
       any  library  function.	All the error names specified by POSIX.1 must
       have distinct values.

       POSIX.1 (2001 edition) lists the following symbolic error  names.   Of
       these,  EDOM  and ERANGE are in the ISO C standard.  ISO C Amendment 1
       defines the additional error number EILSEQ for coding errors in multi-
       byte or wide characters.


       E2BIG  Arg list too long

       EACCES Permission denied

       EADDRINUSE
	      Address in use

       EADDRNOTAVAIL
	      Address not available

       EAFNOSUPPORT
	      Address family not supported

       EAGAIN Resource temporarily unavailable

       EALREADY
	      Connection already in progress

       EBADF  Bad file descriptor

       EBADMSG
	      Bad message

       EBUSY  Resource busy

       ECANCELED
	      Operation canceled

       ECHILD No child processes

       ECONNABORTED
	      Connection aborted

       ECONNREFUSED
	      Connection refused

       ECONNRESET
	      Connection reset

       EDEADLK
	      Resource deadlock avoided

       EDESTADDRREQ
	      Destination address required

       EDOM   Domain error

       EDQUOT Reserved

       EEXIST File exists

       EFAULT Bad address

       EFBIG  File too large

       EHOSTUNREACH
	      Host is unreachable

       EIDRM  Identifier removed

       EILSEQ Illegal byte sequence

       EINPROGRESS
	      Operation in progress

       EINTR  Interrupted function call

       EINVAL Invalid argument

       EIO    Input/output error

       EISCONN
	      Socket is connected

       EISDIR Is a directory

       ELOOP  Too many levels of symbolic links

       EMFILE Too many open files

       EMLINK Too many links

       EMSGSIZE
	      Inappropriate message buffer length

       EMULTIHOP
	      Reserved

       ENAMETOOLONG
	      Filename too long

       ENETDOWN
	      Network is down

       ENETRESET
	      Connection aborted by network

       ENETUNREACH
	      Network unreachable

       ENFILE Too many open files in system

       ENOBUFS
	      No buffer space available

       ENODATA
	      No message is available on the STREAM head read queue

       ENODEV No such device

       ENOENT No such file or directory

       ENOEXEC
	      Exec format error

       ENOLCK No locks available

       ENOLINK
	      Reserved

       ENOMEM Not enough space

       ENOMSG No message of the desired type

       ENOPROTOOPT
	      Protocol not available

       ENOSPC No space left on device

       ENOSR  No STREAM resources

       ENOSTR Not a STREAM

       ENOSYS Function not implemented

       ENOTCONN
	      The socket is not connected

       ENOTDIR
	      Not a directory

       ENOTEMPTY
	      Directory not empty

       ENOTSOCK
	      Not a socket

       ENOTSUP
	      Not supported

       ENOTTY Inappropriate I/O control operation

       ENXIO  No such device or address

       EOPNOTSUPP
	      Operation not supported on socket

       EOVERFLOW
	      Value too large to be stored in data type

       EPERM  Operation not permitted

       EPIPE  Broken pipe

       EPROTO Protocol error

       EPROTONOSUPPORT
	      Protocol not supported

       EPROTOTYPE
	      Protocol wrong type for socket

       ERANGE Result too large

       EROFS  Read-only file system

       ESPIPE Invalid seek

       ESRCH  No such process

       ESTALE Reserved

       ETIME  STREAM ioctl() timeout

       ETIMEDOUT
	      Operation timed out

       ETXTBSY
	      Test file busy

       EWOULDBLOCK
	      Operation would block (may be same value as EAGAIN)

       EXDEV  Improper link

NOTE
       A common mistake is to do

	      if (somecall() == -1) {
		  printf("somecall() failed\n");
		  if (errno == ...) { ... }
	      }

       where  errno no longer needs to have the value it had upon return from
       somecall().  If the value  of  errno  should  be	 preserved  across  a
       library call, it must be saved:

	      if (somecall() == -1) {
		  int errsv = errno;
		  printf("somecall() failed\n");
		  if (errsv == ...) { ... }
	      }


SEE ALSO
       perror(3), strerror(3)



				  2002-10-05			     ERRNO(3)