open

Syntax

#include <fcntl.h>
#include <sys/stat.h> /* for mode definitions */

int open(const char *file, int mode /*, int permissions */);

Description

This function opens the named file in the given mode, which is any combination of the following:

O_RDONLY

The file is opened for reading.

O_WRONLY

The file is opened for writing.

O_RDWR

The file is opened for both reading and writing.

O_CREAT

If the file does not exist, it is created. See section creat.

O_TRUNC

If the file does exist, it is truncated to zero bytes.

O_EXCL

If the file exists, and O_CREAT is also specified, the open call will fail.

O_APPEND

The file pointer is positioned at the end of the file before each write.

O_TEXT

The file is opened in text mode, meaning that Ctrl-M characters are stripped on reading and added on writing as needed. The default mode is specified by the _fmode variable section _fmode.

O_BINARY

The file is opened in binary mode. When called to open the console in binary mode, open will disable the generation of SIGINT when you press Ctrl-C (Ctrl-Break will still cause SIGINT), because many programs that use binary reads from the console will also want to get the `^C' characters. You can use the __djgpp_set_ctrl_c library function (see section __djgpp_set_ctrl_c) if you want Ctrl-C to generate interrupts while console is read in binary mode.

If the file is created by this call, it will be given the read/write permissions specified by permissions, which may be any combination of these values:

S_IRUSR

The file is readable. This is always true for MS-DOS

S_IWUSR

The file is writable.

Other S_I* values may be included, but they will be ignored.

Return Value

If successful, the file descriptor is returned. On error, a negative number is returned and errno is set to indicate the error.

Example

int q = open("/tmp/foo.dat", O_RDONLY|O_BINARY);

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