Microsoft KB Archive/47692

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Errno values are considered valid or invalid under MS-DOS and Windows NT

Article ID: 47692

Article Last Modified on 9/1/2005


  • The C Run-Time (CRT), when used with:
    • Microsoft Visual C++ 1.0 Professional Edition
    • Microsoft Visual C++ 1.5 Professional Edition
    • Microsoft Visual C++ 1.0 Professional Edition
    • Microsoft Visual C++ 2.0 Professional Edition
    • Microsoft Visual C++ 2.1
    • Microsoft Visual C++ 4.0 Standard Edition
    • Microsoft Visual C++ 5.0 Standard Edition
    • Microsoft Visual C++ 6.0 Service Pack 5

This article was previously published under Q47692


When an error occurs in some library routines, the errno variable is set to a value that can be used to indicate the nature of the error. These error codes are defined in the file ERRNO.H. The codes were originally set up for use with UNIX to conform to errors occurring under that operating system. Because of this, and the differences between the various operating systems, many of the codes have no relevance to the MS-DOS and Windows NT environments.

To maintain compatibility with UNIX and XENIX, all the codes, whether meaningful or not, are defined in ERRNO.H. However, in the description of the global variable errno, the CRT documentation included with each of the above products lists only those codes (and their meanings) applicable to the corresponding operating system, either MS-DOS or Windows NT. To output the associated the error messages of these codes, use the perror() function.

If a returned errno value is not one of the listed codes, it can be assumed that the error code was generated incorrectly and is not indicative of the true problem. The documentation for the specific function used denotes which errno values, if any, may be set by an error in that function. The following is a listing of all the errno values defined in ERRNO.H along with brief descriptions of their meanings. Only the values marked with an asterisk (*) are considered valid under MS-DOS. Those marked with a plus sign (+) are considered valid under Windows NT.

For more information on the values not marked with an asterisk or a plus sign, see a UNIX or XENIX system manual.

Value       Define       Description
-----       ------       -----------

EPERM         1          Not owner
ENOENT        2        *+No such file or directory
ESRCH         3          No such process
EINTR         4          Interrupted system call
EIO           5          I/O error
ENXIO         6          No such device or address
E2BIG         7        *+Argument list too long
ENOEXEC       8        *+Exec format error
EBADF         9        *+Bad file number
ECHILD       10         +No spawned processes
EAGAIN       11         +No more processes; not enough memory;
                           maximum nesting level reached
ENOMEM       12        *+Not enough memory
EACCES       13        *+Permission denied
EFAULT       14          Bad address
ENOTBLK      15          Block device required
EBUSY        16          Mount device busy
EEXIST       17        *+File exists
EXDEV        18        *+Cross-device link
ENODEV       19          No such device
ENOTDIR      20          Not a directory
EISDIR       21          Is a directory
EINVAL       22        *+Invalid argument
ENFILE       23          File table overflow
EMFILE       24        *+Too many open files
ENOTTY       25          Not a teletype
ETXTBSY      26          Text file busy
EFBIG        27          File too large
ENOSPC       28        *+No space left on device
ESPIPE       29          Illegal seek
EROFS        30          Read-only file system
EMLINK       31          Too many links
EPIPE        32          Broken pipe
EDOM         33        *+Math argument
ERANGE       34        *+Result too large
EUCLEAN      35          File system needs cleaning
EDEADLK      36         +Resource deadlock would occur
EDEADLOCK    36         *Resource deadlock would occur
ENOLCK       39
ENOSYS       40
EILSEQ       42

* Used under both MS-DOS
+ Used under Windows NT

Note With Visual C++ 32-bit Edition, EDEADLK is the preferred manifest constant for "resource deadlock." However, EDEADLOCK is supported for compatibility with older MS-C versions.

For more information on errno and its possible values, please consult the Visual C++ Book Online.

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