Header File 

errno.h 

Syntax 

extern int _doserrno; 

Description 

_doserrno is a variable that maps many operating system error codes to errno; however, perror does not use _doserrno directly. 

When an operating system call results in an error, _doserrno is set to the actual operating system error code. errno is a parallel error variable inherited from UNIX. 

The following list gives mnemonics for the actual DOS error codes to which _doserrno can be set. (This value of _doserrno may or may not be mapped (through errno) to an equivalent error message string in _sys_errlist.