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_doserrno, errno, _sys_errlist, and _sys_nerr

These global variables hold error codes used by the perror and strerror functions for printing error messages. Manifest constants for these variables are declared in STDLIB.H as follows:

extern int _doserrno;
extern int errno;
extern char *_sys_errlist[ ];
extern int _sys_nerr;

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. All errno values, defined as manifest constants in ERRNO.H, are UNIX-compatible. The values valid for 32-bit Windows applications are a subset of these UNIX values.

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 only, use _doserrno to access the operating-system error-code equivalents of errno codes. For other 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.

The following errno values are compatible with 32-bit Windows applications. Only ERANGE and EDOM are specified in the ANSI standard.

Constant System error message Value
E2BIG Argument list too long 7
EACCES Permission denied 13
EAGAIN No more processes or not enough memory or maximum nesting level reached 11
EBADF Bad file number 9
ECHILD No spawned processes 10
EDEADLOCK Resource deadlock would occur 36
EDOM Math argument 33
EEXIST File exists 17
EINVAL Invalid argument 22
EMFILE Too many open files 24
ENOENT No such file or directory 2
ENOEXEC Exec format error 8
ENOMEM Not enough memory 12
ENOSPC No space left on device 28
ERANGE Result too large 34
EXDEV Cross-device link 18

See Also

Global Variables

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