The _fmode variable sets the default file-translation mode for text or binary translation. This global variable has been deprecated for the more secure functional versions _get_fmode and _set_fmode, which should be used in place of the global variable. It is declared in Stdlib.h as follows.
The default setting of _fmode is _O_TEXT for text-mode translation. _O_BINARY is the setting for binary mode.
You can change the value of _fmode in three ways:
Link with Binmode.obj. This changes the initial setting of _fmode to _O_BINARY, causing all files except stdin, stdout, and stderr to be opened in binary mode.
Make a call to _get_fmode or _set_fmode to get or set the _fmode global variable, respectively.
Change the value of _fmode directly by setting it in your program.