Low-Level File IO

Opening files

open

#include <fcntl.h>
...
int open(const char *filename, int flags [, mode_t mode])

    flags: O_RDONLY, O_WRONLY, O_RDWR, O_CREAT, O_TRUNC, zO_APPEND

• Opens or creates a raw data file.
• Returns -1 on error.

Reading files

read

#include <unistd.h> 
...
ssize_t read(int filedes, void *buffer, size_t size)

• Reads from a raw data file.
• Does not automatically add an end-of-string character.
• Returns the number of bytes read.
• Returns 0 on end-of-file, and -1 on error.

pread

ssize_t pread (int filedes, void *buffer, size_t size, off_t offset)

Writing files

write

#include <unistd.h> 
...
ssize_t write(int filedes, const void *buffer, size_t size)

• Writes to a raw data file.
• Returns the number of bytes written.
• Returns -1 on error.

pwrite

ssize_t pwrite (int filedes, const void *buffer, size_t size, off_t offset)

Seeking

lseek

#include <unistd.h> 
...
off_t lseek (int filedes, off_t offset, int whence)

    whence (offset is relative to)
        SEEK_SET: Beginning of the file.
        SEEK_CUR: Current file position.
        SEEK_END: End of the file.

• Sets the file position.
• Returns the resulting file position.

Closing files

close

#include <unistd.h> 
...
int close (int filedes)

• Closes a raw data file.