SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);
int creat(const char *pathname, mode_t mode);
Given a pathname for a file, open() returns a file descriptor,
The argument flags must include one of the following access modes:
O_RDONLY, O_WRONLY, or O_RDWR. These request opening the file read-
only, write-only, or read/write, respectively.
O_EXCL Ensure that this call creates the file: if this flag is speci‐
fied in conjunction with O_CREAT, and pathname already exists,
then open() will fail.
RETURN VALUE
open() and creat() return the new file descriptor, or -1 if an error
occurred (in which case, errno is set appropriately).
#include <unistd.h>
int close(int fd);
RETURN VALUE
close() returns zero on success. On error, -1 is returned, and errno
is set appropriately.
#include <unistd.h>
ssize_t read(int fd, void *buf, size_t count);
DESCRIPTION
read() attempts to read up to count bytes from file descriptor fd into
the buffer starting at buf.
RETURN VALUE
On success, the number of bytes read is returned (zero indicates end of
file), and the file position is advanced by this number. It is not an
error if this number is smaller than the number of bytes requested;
this may happen for example because fewer bytes are actually available
right now (maybe because we were close to end-of-file, or because we
are reading from a pipe, or from a terminal), or because read() was
interrupted by a signal. On error, -1 is returned, and errno is set
appropriately. In this case it is left unspecified whether the file
position (if any) changes.
SYNOPSIS
#include <unistd.h>
ssize_t write(int fd, const void *buf, size_t count);
DESCRIPTION
write() writes up to count bytes from the buffer pointed buf to the
file referred to by the file descriptor fd.
RETURN VALUE
On success, the number of bytes written is returned (zero indicates
nothing was written). On error, -1 is returned, and errno is set
appropriately.
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fd, off_t offset, int whence);
DESCRIPTION
The lseek() function repositions the offset of the open file associated
with the file descriptor fd to the argument offset according to the
directive whence as follows:
SEEK_SET
The offset is set to offset bytes.
SEEK_CUR
The offset is set to its current location plus offset bytes.
SEEK_END
The offset is set to the size of the file plus offset bytes.
RETURN VALUE
Upon successful completion, lseek() returns the resulting offset loca‐
tion as measured in bytes from the beginning of the file. On error,
the value (off_t) -1 is returned and errno is set to indicate the
error.