IPC 之管道

#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>

void    client(int, int), server(int, int);

int
main(int argc, char **argv)
{
        int             pipe1[2], pipe2[2];
        pid_t   childpid;

        pipe(pipe1);    /* create two pipes */
        pipe(pipe2);

        if ( (childpid = fork()) == 0) {                /* child */
                close(pipe1[1]);
                close(pipe2[0]);

                server(pipe1[0], pipe2[1]);
                exit(0);
        }
                /* 4parent */
        close(pipe1[0]);
        close(pipe2[1]);

        client(pipe2[0], pipe1[1]);

        waitpid(childpid, NULL, 0);             /* wait for child to terminate */
        exit(0);
}

mainpipe.c

// ubuntu16.04 pipe 默認是半雙工管道  

man pipe

pipe()  creates  a  pipe,  a unidirectional data channel that can be used for interprocess communication.

 

 

client.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define MAXLINE 128

void
client(int readfd, int writefd)
{
        size_t  len;
        ssize_t n;
        char    buff[MAXLINE];

                /* 4read pathname */
        fgets(buff, MAXLINE, stdin);
        len = strlen(buff);             /* fgets() guarantees null byte at end */
        if (buff[len-1] == '\n')
                len--;                          /* delete newline from fgets() */

                /* 4write pathname to IPC channel */
        write(writefd, buff, len);

                /* 4read from IPC, write to standard output */
        while ( (n = read(readfd, buff, MAXLINE)) > 0)
                write(STDOUT_FILENO, buff, n);
}

 

server.c

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "my_err.h"

#define MAXLINE 128

void
server(int readfd, int writefd)
{
        int             fd;
        ssize_t n;
        char    buff[MAXLINE+1];

                /* 4read pathname from IPC channel */
        if ( (n = read(readfd, buff, MAXLINE)) == 0)
                err_quit("end-of-file while reading pathname");
        buff[n] = '\0';         /* null terminate pathname */

        if ( (fd = open(buff, O_RDONLY)) < 0) {
                        /* 4error: must tell client */
                snprintf(buff + n, sizeof(buff) - n, ": can't open, %s\n",
                                 strerror(errno));
                n = strlen(buff);
                write(writefd, buff, n);

        } else {
                        /* 4open succeeded: copy file to IPC channel */
                while ( (n = read(fd, buff, MAXLINE)) > 0)
                        write(writefd, buff, n);
                close(fd);
        }
}

gcc -o mainpipe mainpipe.c client.c server.c

./mainpipe

/etc/issue

Ubuntu 16.04.5 LTS \n \l

 

./mainpipe

/no/such/file

/no/such/file: can't open, No such file or directory

 

popen 與 pclose

popen 創建一個管道並啓動一個進程，改進程要麼從管道讀出標準輸入，要麼往管道寫入標準輸出。

FILE *popen(const char *command, const char *type);

int pclose(FILE *stream);

type is "r", calling process read the stdout of command

type is "w", calling process write to the stdin of the command

客戶-服務器程序

#include "unistd.h"
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#define MAXLINE 128

int
main(int argc, char **argv)
{
        size_t  n;
        char    buff[MAXLINE], command[MAXLINE];
        FILE    *fp;

                /* 4read pathname */
        fgets(buff, MAXLINE, stdin);
        n = strlen(buff);               /* fgets() guarantees null byte at end */
        if (buff[n-1] == '\n')
                n--;                            /* delete newline from fgets() */

        snprintf(command, sizeof(command), "cat %s", buff);
        fp = popen(command, "r");

                /* 4copy from pipe to standard output */
        while (fgets(buff, MAXLINE, fp) != NULL)
                fputs(buff, stdout);

        pclose(fp);
        exit(0);
}

gcc -g -o mainpopen mainpopen.c

./mainpopen

/etc/issue