Question

Q4) Write a C program named "hw3q4.c” that takes three string inputs from the command line arguments that represent file names. The first and second files contain four sorted integer numbers that represent set elements. The main process creates a child process that shares the three files. The child process determines the intersection set of two sets and saves the line: "Child process PID: xxxx Intersection of (x, x, x, x) and (y, y, y, y) (z, z, z, z)" in the third file, then terminates. Meanwhile, the parent process computes the union of the two sets concurrently with the child process, then it waits till the child process terminates. After that, it saves to the third file the line: "Parent process PID: xxxx Union of {x, x, x, x} and {y, y, y, y} = {z, z, z, z, z)" and terminates. Use only Unix I/O functions. The program should check for all possible errors and mistakes and display correct and clear error messages. Include the source file to the report. Show the compilation and linking commands in your report. Test your run several times with all search possibilities and show your test results in the report.

Answer 1

The code is followed by the output snapshot

/* File: hw3q4.c */
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
    char buf[1024];
    int buflength;

    int s1[4], s2[4];
    int sr[8], srsize; /* result */

    int fd1, fd2, fd3; /* file descriptors */

    pid_t pid;

    int i, j, k;
    int status;
    char * s;
    /* check for command line arguments */
    if(argc < 4)
    {
        sprintf(buf, "Usage: %s <file1> <file2> <file3>\n", argv[0]);
        buflength = strlen(buf);
        write(1, buf, buflength);
        return -1;
    }

    /* open fds and check for errors */
    if((fd1 = open(argv[1], O_RDONLY)) < 0)
    {
        sprintf(buf, "Error opening file: %s\n", argv[1]);
        buflength = strlen(buf);
        write(1, buf, buflength);
        return -2;
    }

    if((fd2 = open(argv[2], O_RDONLY)) < 0)
    {
        sprintf(buf, "Error opening file: %s\n", argv[2]);
        buflength = strlen(buf);
        write(1, buf, buflength);
        close(fd1);
        return -2;
    }

    /* create with read, write permissions */
    if((fd3 = open(argv[3], O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR)) < 0)
    {
        sprintf(buf, "Error opening file: %s\n", argv[3]);
        buflength = strlen(buf);
        write(1, buf, buflength);
        close(fd1);
        close(fd2);
        return -3;
    }

    /* read the file contents */
    buflength = read(fd1, buf, 1024);
    for(i = 0, s = buf; i < 4; i++)
    {
        /* parse an integer */
        s1[i] = 0;
        while(*s != ' ' && buflength > 1)
        {
            s1[i] = s1[i] * 10 + (*s - '0');
            s++;
            buflength --;
        }
        while(*s == ' ' && buflength > 1)
        {
            s++; /* skip the whitespace */
            buflength --;
        }

        /* printf("Integer %d: %d\n", i + 1, s1[i]); */
    }

    buflength = read(fd2, buf, 1024);
    for(i = 0, s = buf; i < 4; i++)
    {
        /* parse an integer */
        s2[i] = 0;
        while(*s != ' ' && buflength > 1)
        {
            s2[i] = s2[i] * 10 + (*s - '0');
            s++;
            buflength --;
        }
        s++; /* skip the whitespace */
        buflength --;

        /* printf("Integer %d: %d\n", i + 1, s2[i]); */
    }

    /* fork a child */
    pid = fork();
    if(pid == 0) /* child */
    {
        /* intersection */
        /* printf("Child\n"); */
        i = j = k = srsize = 0;
        while(i < 4 && j < 4)
        {
            if(s1[i] == s2[j])
            {
                sr[k++] = s1[i];
                i++;
                j++;
            }
            else if(s1[i] < s2[j])
            {
                i++;
            }
            else
            {
                j++;
            }
        }
        srsize = k;

        sprintf(buf, "Child process PID: %d Intersection of {", getpid());
    }
    else /* parent */
    {
        /* printf("Parent\n"); */
        /* union */
        i = j = k = srsize = 0;
        while(i < 4 && j < 4)
        {
            if(s1[i] == s2[j])
            {
                sr[k++] = s1[i];
                i++;
                j++;
            }
            else if(s1[i] < s2[j])
            {
                sr[k++] = s1[i++];
            }
            else
            {
                sr[k++] = s2[j++];
            }
        }
        while(i < 4)
        {
            sr[k++] = s1[i++];
        }
        while(j < 4)
        {
            sr[k++] = s2[j++];
        }
        srsize = k;

        sprintf(buf, "Parent process PID: %d Intersection of {", getpid());
    }

    /* Prepare the text for writing */
    for(i = 0; i < 4; i++)
    {
        if(i == 0)
            sprintf(buf, "%s%d", buf, s1[i]);
        else
            sprintf(buf, "%s,%d", buf, s1[i]);
    }
    sprintf(buf, "%s} and {", buf);

    for(i = 0; i < 4; i++)
    {
        if(i == 0)
            sprintf(buf, "%s%d", buf, s2[i]);
        else
            sprintf(buf, "%s,%d", buf, s2[i]);
    }
    sprintf(buf, "%s} = {", buf);

    for(i = 0; i < srsize; i++)
    {
        if(i == 0)
            sprintf(buf, "%s%d", buf, sr[i]);
        else
            sprintf(buf, "%s,%d", buf, sr[i]);
    }

    sprintf(buf, "%s}\n", buf);
    buflength = strlen(buf);

    if(pid == 0) /* child */
    {
        /* write immediately */
        write(fd3, buf, buflength);
        /* printf("Child done\n"); */
    }
    else
    {
        /* wait for child to finish */
        wait(&status);
        /* write to file */
        write(fd3, buf, buflength);
        /* printf("Parent done\n"); */
    }
    /* close fds */
    close(fd1);
    close(fd2);
    close(fd3);
    return 0;
}