Some functions in the library set the global variable errno when an error occurs. The file, <errno.h>, provides symbolic names for various error codes.
errno global variable is not safe to use in a threaded or multi-task system. A race condition can occur if a task is interrupted between the call which sets error and when the task examines errno. If another task changes errno during this time, the result will be incorrect for the interrupted task. Definition in file errno.h.
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| Variables | |
| int | errno | 
| number of last error | |
| Error numbers | |
| #define | E2BIG (1) | 
| Argument list too long. | |
| #define | EACCES (2) | 
| Permission denied. | |
| #define | EADDRINUSE (3) | 
| Address in use. | |
| #define | EADDRNOTAVAIL (4) | 
| Address not available. | |
| #define | EAFNOSUPPORT (5) | 
| Address family not supported. | |
| #define | EAGAIN (6) | 
| Resource unavailable, try again (may be the same value as [EWOULDBLOCK]). | |
| #define | EALREADY (7) | 
| Connection already in progress. | |
| #define | EBADF (8) | 
| Bad file descriptor. | |
| #define | EBADMSG (9) | 
| Bad message. | |
| #define | EBUSY (10) | 
| Device or resource busy. | |
| #define | ECANCELED (11) | 
| Operation canceled. | |
| #define | ECHILD (12) | 
| No child processes. | |
| #define | ECONNABORTED (13) | 
| Connection aborted. | |
| #define | ECONNREFUSED (14) | 
| Connection refused. | |
| #define | ECONNRESET (15) | 
| Connection reset. | |
| #define | EDEADLK (16) | 
| Resource deadlock would occur. | |
| #define | EDESTADDRREQ (17) | 
| Destination address required. | |
| #define | EMFILE (18) | 
| File descriptor value too large. | |
| #define | EDQUOT (19) | 
| Reserved. | |
| #define | EEXIST (20) | 
| File exists. | |
| #define | EFAULT (21) | 
| Bad address. | |
| #define | EFBIG (22) | 
| File too large. | |
| #define | EHOSTUNREACH (23) | 
| Host is unreachable. | |
| #define | EIDRM (24) | 
| Identifier removed. | |
| #define | EILSEQ (25) | 
| Illegal byte sequence. | |
| #define | EINPROGRESS (26) | 
| Operation in progress. | |
| #define | EINTR (27) | 
| Interrupted function. | |
| #define | EINVAL (28) | 
| Invalid argument. | |
| #define | EIO (29) | 
| I/O error. | |
| #define | EISCONN (30) | 
| Socket is connected. | |
| #define | EISDIR (31) | 
| Is a directory. | |
| #define | ELOOP (32) | 
| Too many levels of symbolic links. | |
| #define | EDOM (33) | 
| Mathematics argument out of domain of function. | |
| #define | ERANGE (34) | 
| Result too large. | |
| #define | EMSGSIZE (35) | 
| Message too large. | |
| #define | EMULTIHOP (36) | 
| Reserved. | |
| #define | ENAMETOOLONG (37) | 
| Filename too long. | |
| #define | ENETDOWN (38) | 
| Network is down. | |
| #define | ENETRESET (39) | 
| Connection aborted by network. | |
| #define | ENETUNREACH (40) | 
| Network unreachable. | |
| #define | ENFILE (41) | 
| Too many files open in system. | |
| #define | ENOBUFS (42) | 
| No buffer space available. | |
| #define | ENODATA (43) | 
| [OB XSR] [Option Start] No message is available on the STREAM head read queue.  More... | |
| #define | ENODEV (44) | 
| No such device. | |
| #define | ENOENT (45) | 
| No such file or directory. | |
| #define | ENOEXEC (46) | 
| Executable file format error. | |
| #define | ENOLCK (47) | 
| No locks available. | |
| #define | ENOLINK (48) | 
| Reserved. | |
| #define | ENOMEM (49) | 
| Not enough space. | |
| #define | ENOMSG (50) | 
| No message of the desired type. | |
| #define | ENOPROTOOPT (51) | 
| Protocol not available. | |
| #define | ENOSPC (52) | 
| No space left on device. | |
| #define | ENOSR (53) | 
| [OB XSR] [Option Start] No STREAM resources.  More... | |
| #define | ENOSTR (54) | 
| [OB XSR] [Option Start] Not a STREAM.  More... | |
| #define | ENOSYS (55) | 
| Function not supported. | |
| #define | ENOTCONN (56) | 
| The socket is not connected. | |
| #define | ENOTDIR (57) | 
| Not a directory or a symbolic link to a directory. | |
| #define | ENOTEMPTY (58) | 
| Directory not empty. | |
| #define | ENOTRECOVERABLE (59) | 
| State not recoverable. | |
| #define | ENOTSOCK (60) | 
| Not a socket. | |
| #define | ENOTSUP (61) | 
| Not supported (may be the same value as [EOPNOTSUPP]). | |
| #define | ENOTTY (62) | 
| Inappropriate I/O control operation. | |
| #define | ENXIO (63) | 
| No such device or address. | |
| #define | EOPNOTSUPP (64) | 
| Operation not supported on socket (may be the same value as [ENOTSUP]). | |
| #define | EOVERFLOW (65) | 
| Value too large to be stored in data type. | |
| #define | EOWNERDEAD (66) | 
| Previous owner died. | |
| #define | EPERM (67) | 
| Operation not permitted. | |
| #define | EPIPE (68) | 
| Broken pipe. | |
| #define | EPROTO (69) | 
| Protocol error. | |
| #define | EPROTONOSUPPORT (70) | 
| Protocol not supported. | |
| #define | EPROTOTYPE (71) | 
| Protocol wrong type for socket. | |
| #define | EMLINK (72) | 
| Too many links. | |
| #define | EROFS (73) | 
| Read-only file system. | |
| #define | ESPIPE (74) | 
| Invalid seek. | |
| #define | ESRCH (75) | 
| No such process. | |
| #define | ESTALE (76) | 
| Reserved. | |
| #define | ETIME (77) | 
| [OB XSR] [Option Start] Stream ioctl() timeout.  More... | |
| #define | ETIMEDOUT (78) | 
| Connection timed out. | |
| #define | ETXTBSY (79) | 
| Text file busy. | |
| #define | EWOULDBLOCK (80) | 
| Operation would block (may be the same value as [EAGAIN]). | |
| #define | EXDEV (81) | 
| Cross-device link. | |
| #define | EHOSTDOWN (82) | 
| Host is down. | |
| #define | EPFNOSUPPORT (83) | 
| Protocol family not supported. | |
| #define | ETOOMANYREFS (84) | 
| Too many references: cannot splice. | |