Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 47)

CS485G Spring 2015 47

(a) open() and close(): open() returns a ﬁle descriptor; the

kernel allocates and initializes a data structure. close() lets

the kernel deallocate the structure.

(b) read() and write()

1 #include <unistd.h> // defines ssize_t: signed integer

2 char buf[512];

3 int fd1, fd2;

4 ssize_t nbytes;

5 if ((fd1 = open("/etc/hosts", O_RDONLY) < 0)) {

6 perror("/etc/hosts");

7 exit(1);

8 }

9 if ((nbytes = read(fd1, buf, sizeof(buf))) < 0) {

10 perror("read");

11 exit(1);

12 }

13 if ((fd2 = creat("/tmp/hosts", 0664)) < 0)) {

14 perror("/tmp/hosts");

15 exit(1);

16 }

17 if ((nbytes = write(fd2, buf, nbytes) != nbytes) {

18 perror("write");

19 exit(1);

20 }

A value of nbytes less than sizeof(buf) is valid.

53 Sockets

1. Lecture 28, 4/8/2015

2. A socket is an abstraction that lets two processes communicate, even

if they are on different machines.

3. Setting up a socket is asymmetric; the client and the server do dif-

ferent things, after which both can read() and write().

4. Client

(a) socket() to create a local ﬁle descriptor (like “buy a phone”)

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Cirrus Logic CS485 Manual de usuario Pagina 47