errno, _doserrno, _sys_errlist, and _sys_nerr
These global variables hold error codes used by the perror and strerror functions for printing error messages. The more secure functional versions listed in this table should be used in place of their global variable.
Global Variable |
Functional Equivalents |
|---|---|
_doserrno |
|
_errno |
These variables are declared in STDLIB.H as
extern int _doserrno;
extern int errno;
extern char *_sys_errlist[ ];
extern int _sys_nerr;
Remarks
errno and _errno are connected to the same variable. errno is defined with the code #define errno (*_errno())
errno is set on an error in a system-level call. Because errno holds the value for the last call that set it, this value may be changed by succeeding calls. Always check errno immediately before and after a call that may set it.
On an error, errno is not necessarily set to the same value as the error code returned by a system call. For I/O operations, use _doserrno to access the operating-system error-code equivalents of errno codes. For most non-I/O operations the value of _doserrno is undefined.
Each errno value is associated with an error message that can be printed using perror or stored in a string using strerror. perror and strerror use the _sys_errlist array and _sys_nerr, the number of elements in _sys_errlist, to process error information.
Library math routines set errno by calling _matherr. To handle math errors differently, write your own routine according to the _matherr reference description and name it _matherr.
All errno values, defined as predefined constants in ERRNO.H, are UNIX-compatible and are listed below. Only ERANGE, EILSEQ and EDOM are specified in the ANSI standard.
Constant |
System error message |
Value |
|---|---|---|
EPERM |
Operation not permitted |
1 |
ENOENT |
No such file or directory |
2 |
ESRCH |
No such process |
3 |
EINTR |
Interrupted function |
4 |
EIO |
I/O error |
5 |
ENXIO |
No such device or address |
6 |
E2BIG |
Argument list too long |
7 |
ENOEXEC |
Exec format error |
8 |
EBADF |
Bad file number |
9 |
ECHILD |
No spawned processes |
10 |
EAGAIN |
No more processes or not enough memory or maximum nesting level reached |
11 |
ENOMEM |
Not enough memory |
12 |
EACCES |
Permission denied |
13 |
EFAULT |
Bad address |
14 |
EBUSY |
Device or resource busy |
16 |
EEXIST |
File exists |
17 |
EXDEV |
Cross-device link |
18 |
ENODEV |
No such device |
19 |
ENOTDIR |
Not a directory |
20 |
EISDIR |
Is a directory |
21 |
EINVAL |
Invalid argument |
22 |
ENFILE |
Too many files open in system |
23 |
EMFILE |
Too many open files |
24 |
ENOTTY |
Inappropriate I/O control operation |
25 |
EFBIG |
File too large |
27 |
ENOSPC |
No space left on device |
28 |
ESPIPE |
Invalid seek |
29 |
EROFS |
Read-only file system |
30 |
EMLINK |
Too many links |
31 |
EPIPE |
Broken pipe |
32 |
EDOM |
Math argument |
33 |
ERANGE |
Result too large |
34 |
EDEADLK |
Resource deadlock would occur |
36 |
EDEADLOCK |
Same as EDEADLK for compatibility with older Microsoft C versions |
36 |
ENAMETOOLONG |
Filename too long |
38 |
ENOLCK |
No locks available |
39 |
ENOSYS |
Function not supported |
40 |
ENOTEMPTY |
Directory not empty |
41 |
EILSEQ |
Illegal byte sequence |
42 |
STRUNCATE |
String was truncated |
80 |