File Constants
#include <fcntl.h>
Remarks
The integer expression formed from one or more of these constants determines the type of reading or writing operations permitted. It is formed by combining one or more constants with a translation-mode constant.
The file constants are as follows:
_O_APPEND
Repositions the file pointer to the end of the file before every write operation._O_CREAT
Creates and opens a new file for writing; this has no effect if the file specified by filename exists._O_EXCL
Returns an error value if the file specified by filename exists. Only applies when used with _O_CREAT._O_RDONLY
Opens file for reading only; if this flag is given, neither _O_RDWR nor _O_WRONLY can be given._O_RDWR
Opens file for both reading and writing; if this flag is given, neither _O_RDONLY nor _O_WRONLY can be given._O_TRUNC
Opens and truncates an existing file to zero length; the file must have write permission. The contents of the file are destroyed. If this flag is given, you cannot specify _O_RDONLY._O_WRONLY
Opens file for writing only; if this flag is given, neither _O_RDONLY nor _O_RDWR can be given.