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File Constants | Microsoft Docs |
11/04/2016 |
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article |
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c8fa5548-9ac2-4217-801d-eb45e86f2fa4 |
6 |
corob-msft |
corob |
ghogen |
#include <fcntl.h>
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.