Files that are organized as a sequence of data are called regular files. Regular files can contain ASCII text, text in some other binary data encoding, executable code, or any combination of text, data, and code.
A regular file is made up of the following components:
Control data, which is called the inode. This data includes the file type, the access permissions, the owner, the file size, and the location of the data blocks.
File contents: a nonterminated sequence of bytes.
The Solaris operating system provides the following basic forms of file input/output interfaces:
The traditional, raw style of file I/O is described in Basic File I/O.
The standard I/O buffering provides an easier interface and improved efficiency to an application run on a system without virtual memory. In an application running in a virtual memory environment, such as on the SunOS operating system, standard file I/O is outdated.
The memory mapping interface is described in Memory Management Interfaces. Mapping files is the most efficient form of file I/O for most applications run under the SunOS platform.
The following interfaces perform basic operations on files and on character I/O devices.
Table 6–1 Basic File I/O Interfaces
Interface Name |
Purpose |
---|---|
Open a file for reading or writing |
|
Close a file descriptor |
|
Read from a file |
|
Write to a file |
|
Create a new file or rewrite an existing one |
|
Remove a directory entry |
|
Move read/write file pointer |
The following code sample demonstrates the use of the basic file I/O interface. read(2) and write(2) both transfer no more than the specified number of bytes, starting at the current offset into the file. The number of bytes actually transferred is returned. The end of a file is indicated on a read(2) by a return value of zero.
#include <fcntl.h> #define MAXSIZE 256 main() { int fd; ssize_t n; char array[MAXSIZE]; fd = open ("/etc/motd", O_RDONLY); if (fd == -1) { perror ("open"); exit (1); } while ((n = read (fd, array, MAXSIZE)) > 0) if (write (1, array, n) != n) perror ("write"); if (n == -1) perror ("read"); close (fd); }
When you are done reading or writing a file, always call close(2). Do not call close(2) for a file descriptor that was not returned from a call to open(2).
File pointer offsets into an open file are changed by using read(2), write(2), or by calls to lseek(2). The following example demonstrates the uses of lseek.
off_t start, n; struct record rec; /* record current offset in start */ start = lseek (fd, 0L, SEEK_CUR); /* go back to start */ n = lseek (fd, -start, SEEK_SET); read (fd, &rec, sizeof (rec)); /* rewrite previous record */ n = lseek (fd, -sizeof (rec), SEEK_CUR); write (fd, (char *&rec, sizeof (rec));
The following table lists the tasks performed by advanced file I/O interfaces.
Table 6–2 Advanced File I/O Interfaces
Interface Name |
Purpose |
---|---|
Link to a file |
|
Determine accessibility of a file |
|
Make a special or ordinary file |
|
Change mode of file |
|
Change owner and group of a file |
|
Set file access and modification times |
|
Get file status |
|
Perform file control functions |
|
Control device |
|
Get configurable path name variables |
|
Perform directory operations |
|
Make a directory |
|
Read the value of a symbolic link |
|
Change the name of a file |
|
Remove a directory |
|
Make a symbolic link to a file |
The file system control interfaces listed in the following table enable the control of various aspects of the file system.
Table 6–3 File System Control Interfaces
Interface Name |
Purpose |
---|---|
Get file system statistics |
|
Update super block |
|
Mount a file system |
|
Get file system information |
|
Get file system type information |