管道的简单应用

 

/**
 * 父进程写入子进程读取
 */

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

int main()
{
        int mypipe[2];
        //创建管道
        if(pipe(mypipe) < 0){
                perror("create pipe error");
                exit(1);
        }
        pid_t pid;
        if((pid = fork()) < 0){
                perror("fork error");
                exit(2);
        }
        //parent process
        if(pid > 0){
                close(mypipe[0]);
                //...
                int start = 1, end = 10000;

/*
                if(write(mypipe[1], &start, sizeof(start)) != sizeof(int)){
                        perror("write error");
                        exit(3);
                }
                if(write(mypipe[1], &end, sizeof(end)) != sizeof(int)){
                        perror("write error");
                        exit(3);
                }
*/

                FILE *fp = fdopen(mypipe[1], "wb");
                int ret = fprintf(fp, "%d,%d", start, end);
                printf("ret=%d\n", ret);
                fclose(fp);

                wait((void *)0);
                close(mypipe[1]);
        }else{
                close(mypipe[1]);
                //...

                int start = 0, end = 0;

                /*
                if(read(mypipe[0], &start, sizeof(int)) < 0){
                        perror("read error");
                        exit(4);
                }
                if(read(mypipe[0], &end, sizeof(int)) < 0){
                        perror("read error");
                        exit(4);
                }
                */

                FILE *fp = fdopen(mypipe[0], "rb");
                int ret = fscanf(fp, "%d,%d", &start, &end);
                printf("ret=%d\n", ret);
                fclose(fp);

                fprintf(stderr, "start=%d, end=%d\n", start, end);
                close(mypipe[0]);
        }
        return 0;
}

 

 

 

/**
 * 一个子进程读取文件，一个子进程grep
 */

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

char *cmd1[3] = {
        "/bin/cat", "/etc/passwd", NULL
};
char *cmd2[4] = {
        "/bin/grep", "root", "--color", NULL
};

int main()
{
        int mypipe[2];
        if(pipe(mypipe) < 0){
                perror("pipe error");
                exit(1);
        }
        int i = 0;
        pid_t pid;
        for(; i < 2; i++){
                pid = fork();
                if(pid < 0){
                        perror("fork error");
                        exit(1);
                }else if(pid > 0){
                        if(i == 1){
                                close(mypipe[0]);
                                close(mypipe[1]);
                                wait(0);
                                wait(0);
                        }
                }else{
                        if(i == 0){
                                /**
                                 * cat 默认将数据写入标准输出，所以可以将标准输出重定向到管道
                                 */
                                close(mypipe[0]);
                                if(dup2(mypipe[1], STDOUT_FILENO) 
                                                                        != STDOUT_FILENO){
                                        perror("dup2 STDOUT_FILENO error");
                                        exit(1);
                                }
                                close(mypipe[1]);
                                if(execvp(cmd1[0], cmd1)){
                                        perror("execvp error");
                                        exit(1);
                                }
                        }else{
                                /**
                                 * grep 默认是从标准输入读取
                                 */
                                close(mypipe[1]);
                                if(dup2(mypipe[0], STDIN_FILENO) 
                                                                        != STDIN_FILENO){
                                        perror("dup2 STDIN_FILENO error");
                                        exit(1);
                                }
                                close(mypipe[0]);
                                if(execvp(cmd2[0], cmd2)){
                                        perror("execvp error");
                                        exit(1);
                                }
                        }
                }
        }
        return 0;
}

 

协同程序

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

int main(){
        int fda[2], fdb[2];
        if(pipe(fda) < 0){
                perror("pipe fda error");
                exit(1);
        }
        if(pipe(fdb) < 0){
                perror("pipe fdb error");
                exit(1);
        }
        pid_t pid;
        pid = fork();
        if(pid < 0){
                perror("fork error");
                exit(1);
        }
        if(pid > 0){
                /**
                 * 1、父进程从标准输入读取x、y
                 * 2、将x、y写入管道a
                 * 3、从管道b读取计算的结果
                 */
                close(fda[0]);
                close(fdb[1]);
                int a, b, ret;
                fprintf(stderr, "Please input a,b:\n");
                fscanf(stdin, "%d,%d", &a, &b);
                if(write(fda[1], &a, sizeof(int)) != sizeof(int)){
                        perror("write error");
                        exit(1);
                }
                if(write(fda[1], &b, sizeof(int)) < sizeof(int)){
                        perror("write error");
                        exit(1);
                }
                if(read(fdb[0], &ret, sizeof(int)) < 0){
                        perror("read error");
                        exit(1);
                }
                printf("ret = %d\n", ret);
                close(fda[1]);
                close(fdb[0]);
                wait(0);
        }else{
                /**
                 * 1、子进程负责从管道a中读取父进程写入的x、y
                 * 2、通过exec调用add进行计算
                 * 3、将计算结果写入b
                 */
                //fda：read，fdb：写
                close(fda[1]);
                close(fdb[0]);

                if(dup2(fda[0], STDIN_FILENO) != STDIN_FILENO){
                        perror("dup2 error");
                        exit(1);
                }
                if(dup2(fdb[1], STDOUT_FILENO) != STDOUT_FILENO){
                        perror("dup2 error");
                        exit(1);
                }
                char *cmd[] = {
                        "/root/unix/wangyi/src/ipc/collaborative/add", 
                        "/root/unix/wangyi/src/ipc/collaborative/add", NULL
                };
                if(execvp(cmd[0], cmd) < 0){
                        perror("execvp error");
                        exit(1);
                }

                close(fda[0]);
                close(fdb[1]);
        }
        return 0;
}