errno

Synopsis:

#include <errno.h>

int errno;

char * const sys_errlist[];
int sys_nerr;

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The errno variable is set to certain error values by many functions whenever an error has occurred. This variable may be implemented as a macro, but you can always examine or set it as if it were a simple integer variable.

Note:

You can't assume that the value of errno is valid unless the description of the function that you've called explicitly states that this variable will be set following an error and the function call itself indicates that an error has occurred. The runtime library never resets errno to 0.
The documentation for a function might list special meanings for certain values of errno, but this doesn't mean that these are necessarily the only values that the function might set.
Each thread in a multi-threaded program has its own error value in its thread local storage. No matter which thread you're in, you can simply refer to errno— it's defined in such a way that it refers to the correct variable for the thread. For more information, see “Local storage for private data” in the documentation for ThreadCreate().

The following variables are also defined in <errno.h>:

sys_errlist: An array of error messages corresponding to errno.
sys_nerr: The number of entries in the sys_errlist array.

The values for errno include at least the following. Some are defined by POSIX, and some are additional values.

Name	Value	Meaning	POSIX?
E2BIG	7	Argument list is too long	Yes
EACCES	13	Permission denied	Yes
EADDRINUSE	248	Address is already in use	Yes
EADDRNOTAVAIL	249	Can't assign requested address	Yes
EADV	68	Advertise error	No
EAFNOSUPPORT	247	Address family isn't supported by protocol family	Yes
EAGAIN	11 (same as EWOULDBLOCK)	Resource is temporarily unavailable; try again	Yes
EALREADY	237	Operation is already in progress	Yes
EBADE	50	Invalid exchange	No
EBADF	9	Bad file descriptor	Yes
EBADFD	81	FD is invalid for this operation	No
EBADFSYS	302	Corrupted filesystem detected	No
EBADMSG	77	Bad message	Yes
EBADR	51	Invalid request descriptor	No
EBADRPC	272	RPC struct is bad	No
EBADRQC	54	Invalid request code	No
EBADSLT	55	Invalid slot	No
EBFONT	57	Bad font-file format	No
EBUSY	16	Device or resource is busy	Yes
ECANCELED	47	Operation canceled	Yes
ECHILD	10	No child processes	Yes
ECHRNG	37	Channel number is out of range	No
ECOMM	70	Communication error occurred on send	No
ECONNABORTED	253	Software caused connection to abort	Yes
ECONNREFUSED	261	Connection refused	Yes
ECONNRESET	254	Connection reset by peer	Yes
ECTRLTERM	310	Remap to the controlling terminal	No
EDEADLK	45	Resource deadlock avoided	Yes
EDEADLOCK	56	File locking deadlock	No
EDESTADDRREQ	239	Destination address is required	Yes
EDOM	33	Math argument is out of domain for the function	Yes
EDQUOT	49	Disk quota exceeded	Yes
EENDIAN	313	Endian not supported	No
EEXIST	17	File exists	Yes
EFAULT	14	Bad address	Yes
EFBIG	27	File is too large	Yes
EFPOS	110	File positioning error	No
EHOSTDOWN	264	Host is down	No
EHOSTUNREACH	265	Unable to communicate with remote node	Yes
EIDRM	36	Identifier removed	Yes
EILSEQ	88	Illegal byte sequence	Yes
EINPROGRESS	236	Operation now in progress	Yes
EINTR	4	Interrupted function call	Yes
EINVAL	22	Invalid argument	Yes
EIO	5	I/O error	Yes
EISCONN	256	Socket is already connected	Yes
EISDIR	21	Is a directory	Yes
EL2HLT	44	Level 2 halted	No
EL2NSYNC	38	Level 2 not synchronized	No
EL3HLT	39	Level 3 halted	No
EL3RST	40	Level 3 reset	No
ELIBACC	83	Can't access shared library	No
ELIBBAD	84	Accessing a corrupted shared library	No
ELIBEXEC	87	Attempting to exec a shared library	No
ELIBMAX	86	Attempting to link in too many libraries	No
ELIBSCN	85	The `.lib` section in a.out is corrupted	No
ELNRNG	41	Link number is out of range	No
ELOOP	90	Too many levels of symbolic links or prefixes	Yes
EMFILE	24	Too many open files	Yes
EMLINK	31	Too many links	Yes
EMORE	309	More to do, send message again	No
EMSGSIZE	240	Inappropriate message buffer length	Yes
EMULTIHOP	74	Multihop attempted	Yes
ENAMETOOLONG	78	Filename is too long	Yes
ENETDOWN	250	Network is down	Yes
ENETRESET	252	Network dropped connection on reset	Yes
ENETUNREACH	251	Network is unreachable	Yes
ENFILE	23	Too many open files in the system	Yes
ENOANO	53	No anode	No
ENOBUFS	255	No buffer space available	Yes
ENOCSI	43	No CSI structure available	No
ENODATA	61	No data (for no-delay I/O)	Yes
ENODEV	19	No such device	Yes
ENOENT	2	No such file or directory	Yes
ENOEXEC	8	Exec format error	Yes
ENOLCK	46	No locks available	Yes
ENOLIC	311	No license available	No
ENOLINK	67	The link has been severed	Yes
ENOMEM	12	Not enough memory	Yes
ENOMSG	35	No message of desired type	Yes
ENONDP	301	Need an NDP (8087...) to run	No
ENONET	64	Machine isn't on the network	No
ENOPKG	65	Package isn't installed	No
ENOPROTOOPT	242	Protocol isn't available	Yes
ENOREMOTE	300	Must be done on local machine	No
ENOSPC	28	No space left on device	Yes
ENOSR	63	Out of streams resources	Yes
ENOSTR	60	Device isn't a stream	Yes
ENOSYS	89	Function isn't implemented	Yes
ENOTBLK	15	A block device is required	No
ENOTCONN	257	Socket isn't connected	Yes
ENOTDIR	20	Not a directory	Yes
ENOTEMPTY	93	Directory isn't empty	Yes
ENOTRECOVERABLE	95	Mutex-protected state not recoverable	Yes
ENOTSOCK	238	Socket operation on nonsocket	Yes
ENOTSUP	48	Not supported	Yes
ENOTTY	25	Inappropriate I/O control operation	Yes
ENOTUNIQ	80	Given name isn't unique	No
ENXIO	6	No such device or address	Yes
EOK	0	No error	No
EOPNOTSUPP	103	Operation isn't supported	Yes
EOVERFLOW	79	Value too large to be stored in data type	Yes
EOWNERDEAD	58	The owner of a lock died while holding it	No
EPERM	1	Operation isn't permitted	Yes
EPFNOSUPPORT	246	Protocol family isn't supported	No
EPIPE	32	Broken pipe	Yes
EPROCUNAVAIL	276	Bad procedure for program	No
EPROGMISMATCH	275	Program version wrong	No
EPROGUNAVAIL	274	RPC program isn't available	No
EPROTO	71	Protocol error	Yes
EPROTONOSUPPORT	243	Protocol isn't supported	Yes
EPROTOTYPE	241	Protocol is wrong type for socket	Yes
ERANGE	34	Result is too large	Yes
EREMCHG	82	Remote address changed	No
EREMOTE	66	The object is remote	No
ERESTART	91	Restartable system call	No
EROFS	30	Read-only filesystem	Yes
ERPCMISMATCH	273	RPC version is wrong	No
ESHUTDOWN	258	Can't send after socket shutdown	No
ESECTYPEINVAL	314	Invalid security type	No
ESOCKTNOSUPPORT	244	Socket type isn't supported	No
ESPIPE	29	Illegal seek	Yes
ESRCH	3	No such process	Yes
ESRMNT	69	Server mount error	No
ESRVRFAULT	312	The receive side of a message transfer encountered a memory fault accessing the receive/reply buffer.	No
ESTALE	122	Potentially recoverable I/O error	Yes
ESTRPIPE	92	If pipe/FIFO, don't sleep in stream head	No
ETIME	62	Timer expired	Yes
ETIMEDOUT	260	Connection timed out	Yes
ETOOMANYREFS	259	Too many references: can't splice	No
ETXTBSY	26	Text file is busy	Yes
EUNATCH	42	Protocol driver isn't attached	No
EUSERS	94	Too many users (for UFS)	No
EWOULDBLOCK	11 (same as EAGAIN)	Operation would block	Yes
EXDEV	18	Cross-device link	Yes
EXFULL	52	Exchange full	No

Examples:

/*
 *  The following program makes an illegal call
 *  to the close() function, then prints the
 *  value held in errno.
 */
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

int main( void )
{
    int errvalue;

    if( close( -1 ) == -1 ){
        errvalue = errno; // preserve value as first printf may change errno
        printf( "The error generated was %d\n", errvalue );
        printf( "That means: %s\n", strerror( errvalue ) );
    }
}

Classification:

ANSI, POSIX 1003.1