深入理解计算机系统_3e 第十章家庭作业 CS:APP3e chapter 10 homework

10.6

1.若成功打开“foo.txt”：

-->1.1若成功打开“baz.txt”： 输出“4\n”

-->1.2若未能成功打开“baz.txt”： 输出“-1\n”

2.若未能成功打开“foo.txt”：

-->2.1若成功打开“baz.txt”： 输出“3\n”

-->2.2若未能成功打开“baz.txt”： 输出“-1\n”

10.7

#include "csapp.h"

int main(int argc, char **argv) 
{
    int n;
    rio_t rio;
    char buf[MAXBUF];

    Rio_readinitb(&rio, STDIN_FILENO);
    while((n = Rio_readnb(&rio, buf, MAXBUF)) != 0) 
	    Rio_writen(STDOUT_FILENO, buf, n);
    exit(0);
}

10.8

#include "csapp.h"
#include "csapp.c"
#include <string.h>
#include <stdio.h>

int main (int argc, char **argv) 
{
    struct stat stat;
    char *type, *readok;
    char buf[MAXBUF];
    char filename[MAXBUF];
    memset(buf, 0, MAXBUF);
    memset(filename, 0, MAXBUF);

    if (argc != 2)  {
    fprintf(stderr, "usage: %s <descriptor number>\n", argv[0]);
    exit(0);
    }
         
    sprintf(buf+sprintf(buf, "/proc/self/fd/"), argv[1]);

    if(readlink(buf, filename, sizeof(filename)) == -1)
    {
        fprintf(stderr, "bad file descriptor\n");
        exit(EXIT_FAILURE);
    }

    Stat(filename, &stat);
    if (S_ISREG(stat.st_mode))     /* Determine file type */
    type = "regular";
    else if (S_ISDIR(stat.st_mode))
    type = "directory";
    else 
    type = "other";
    if ((stat.st_mode & S_IRUSR)) /* Check read access */
    readok = "yes";
    else
    readok = "no";

    printf("type: %s, read: %s\n", type, readok);
    exit(0);
}

参考：Getting Filename from file descriptor in C

10.9

这里只是模拟一下基本的操作，就是将文价描述符argv[1]（3）指向“foo.txt”（STDIN_FILENO），shell实际实现肯定有许多没写到的。

if (Fork() == 0){ /* child */
  dup2(STDIN_FILENO, atoi(argv[1]));
  Execve("fstatcheck", argv, envp);
}

10.10

如果有infile参数的话，将STDIN_FILENO指向该文件。

#include "csapp.h"

int main(int argc, char **argv) 
{
    int n;
    rio_t rio;
    char buf[MAXLINE];

    if (argc == 2) /* infile */
    {
        int fd = open(argv[1], O_RDONLY|O_CREAT);
        dup2(fd, STDIN_FILENO);
        close(fd);
    }

    Rio_readinitb(&rio, STDIN_FILENO);
    while((n = Rio_readlineb(&rio, buf, MAXLINE)) != 0) 
	    Rio_writen(STDOUT_FILENO, buf, n);

    exit(0);
}