《操作系统导论》第5章作业

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我是靠谱客的博主温暖犀牛，这篇文章主要介绍《操作系统导论》第5章作业，现在分享给大家，希望可以做个参考。

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

int x;

int main(int argc, char *argv[])
{
        printf("This program pid is (%d), x is %dn", (int)getpid(), x);
        int rc = fork();
        if (rc < 0) {
                fprintf(stderr, "fork failedn");
                exit(1);
        } else if (rc == 0) {
                wait(NULL);
                printf("I am child (pid:%d), my x is %dn", (int)getpid(), x);
                x = 3;
                printf("x in child now changed to %dn", x);
        } else {
                x = 100;
                printf("I am parent of %d (pid:%d), my x is %dn", rc, (int)getpid(), x);
        }
        return 0;
}

结果如下图所示：
在这里插入图片描述
可以看出，当主进程改变变量x的值时，子进程x变量的值不会改变，当子进程和父进程都改变x的值时，x在父子进程会分别变成不一样的值。

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

int main(int argc, char *argv[])
{
        char buffer[13];
        int in, out;
        in = open("./52.txt", O_RDONLY);
        out = open("./52.txt", O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
        int cread, pread;
        int rc = fork();
        if (rc < 0) {
                fprintf(stderr, "fork failedn");
                exit(1);
        } else if (rc == 0) {
                cread = read(in, buffer, 13);
                if (cread == -1) {
                        printf("child cannot visit filen");
                } else {
                        printf("child can visit filen");
                }
                write(out, "I am childn", 10);
        } else {
                pread = read(in, buffer, 13);
                if (pread == -1) {
                        printf("parent cannot visit filen");
                } else {
                        printf("parent can visit filen");
                }
                write(out, "I am parentn", 12);
        }
        return 0;
}

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

int main(int argc, char *argv[])
{
        char buffer[13];
        int in, out;
        in = open("./52.txt", O_RDONLY);
        out = open("./52.txt", O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
        int cread, pread;
        int rc = fork();
        if (rc < 0) {
                fprintf(stderr, "fork failedn");
                exit(1);
        } else if (rc == 0) {
                cread = read(in, buffer, 13);
                if (cread == -1) {
                        printf("child cannot visit filen");
                } else {
                        printf("child can visit filen");
                }
                write(out, "I am childn", 10);
        } else {
                pread = read(in, buffer, 13);
                if (pread == -1) {
                        printf("parent cannot visit filen");
                } else {
                        printf("parent can visit filen");
                }
                write(out, "I am parentn", 12);
        }
        return 0;
}

结果如下所示：
在这里插入图片描述

因此，子进程和父进程都可以访问open()返回的文件描述符，当它们并发写入文件时，父子进程都能将内容写入文件。

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

int main(int argc, char *argv[])
{
        printf("This program pid is (%d)n", (int)getpid());
        int rc = vfork();
        if (rc < 0) {
                fprintf(stderr, "fork failedn");
                exit(1);
        } else if (rc == 0) {
                printf("I am child (pid:%d), hellon", (int)getpid());
                exit(0);
        } else {
                printf("I am parent of %d (pid:%d), goodbyen", rc, (int)getpid());
        }
        return 0;
}