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the use of pipe

admin 11月 13, 2020 0

the head file of the pipe() function is <unistd.h> :

#include <unistd.h>

int pipe(int fd[2]);

1. the use of pipe in inter-process communications

Pipe is often used for communications between processes which have genetic relationship with each other. the following is an example given by UNP(II):

#include <unistd.h>      /*pipe() && fork() & write() & read() & STDOOUT_FILENO*/
#include <sys/types.h>  /* pid_t ssize_t*/
#include <sys/wait.h>  /* waitpid() */
#include <stdio.h>    /*fgets(), stdin*/
#include <string.h>  /*strlen*/ 

#define BUFFERSIZE 20

void client(int readfd, int writefd);
void server(int readfd, int writefd);
    
int main(int argc, char *argv[]) {
 int pipe1[2], pipe2[2];
 pid_t child_pid;
 
 pipe(pipe1);  /* create two pipes */
 pipe(pipe2);
 
 if( (child_pid = fork()) == 0) {    /*child process for server */
  close(pipe1[1]);  /* close write fd*/
  close(pipe2[0]);  /* close read fd */
   
  server(pipe1[0], pipe2[1]);  /*read from pipe1[0], and write to pipe2[1]*/
  exit(); 
 }
 
 close(pipe1[1]);
 close(pipe2[0]);
 
 client(pipe1[1], pipe2[0]); /*write to pipe1[0], and read from pipe2[1]*/
 
 waitpid(child_pid, NULL, 0);
 
}

void client(int readfd, int writefd) {
 size_t len;
 ssize_t n;
 char buff[BUFFERSIZE];
 
 fgets(buff, BUFFERSIZE, stdin);
 
 len = strlen(buff);

 if (buff[len-1] == 'n'){
  len--;
 }
 
 write(writefd, buff, len);
 
 while ((n = read(readfd, buff, BUFFERSIZE)) > 0) {
  write(writefd, buff, n);
 }
}

void server(int readfd, int writefd) {
 size_t len;
 ssize_t n;
 int fd;
 char buff[BUFFERSIZE+1];
 
 if (n = read(readfd, buff, BUFFERSIZE) == 0) {
  printf("server read error!");
  eixt(1);
 }
 buff[n] = '