Lab 1, problem2 completed

Labs/Lab1/fork-file.c

+/*
+ * CSCI 315 Operating Systems Design
+ * Date: 2014-09-02
+ * Copyright (c) 2014 Bucknell University
+ *
+ * Permission is hereby granted, free of charge, to any individual or
+ * institution obtaining a copy of this software and associated
+ * documentation files (the "Software"), to use, copy, modify, and
+ * distribute without restriction, provided that this copyright and
+ * permission notice is maintained, intact, in all copies and supporting
+ * documentation.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL BUCKNELL UNIVERSITY BE LIABLE FOR ANY CLAIM, DAMAGES
+ * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
+ * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * Revised by Xiannong Meng
+ * 2017-08-23
+ * added
+ * #include <unistd.h>
+ * #include <sys/types.h>
+ * #include <sys/wait.h>
+ */
+#include <fcntl.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <errno.h>
+#include <unistd.h>
+
+int i = 7;
+double x = 3.14;
+
+int main(int argc, char* argv[]) {
+
+  int pid;
+  int j = 6;
+  double y = 2.18;
+
+  char buf_parent[6];
+  char buf_child[6]; 
+  int status; // exit status to be filled by wait
+
+  // create and open a file called data.txt
+  // use open (file descriptors)
+
+  // write into data.txt the following string:
+  // "this is a test for processes created with fork\nthis is another line"
+
+  // close the file so the writing can complete
+
+  // re-open the file for reading
+  int file_descriptor = open("./data.txt", O_RDWR | O_CREAT);
+  char a_str[] = "this is a test for processes created with fork\nthis is another line";
+  int numBytes_written = write(file_descriptor, a_str, sizeof(a_str));
+  close (file_descriptor);
+  file_descriptor = open("./data.txt", O_RDONLY);
+  
+  
+  if ((pid = fork()) == 0) {
+    // child process
+    // read 5 characters from file into buf_child
+    // print the characters in buf_child to terminal
+    read(file_descriptor, buf_child, 5);
+    printf("%s\n", buf_child);
+
+    printf("pid= %d -- initially, child sees x= %lf, y=%lf\n", pid, x, y);
+    x = 0;
+    y = 0;
+    printf("pid= %d -- child sees x= %lf, y=%lf\n", pid, x, y);
+    printf("child is terminating\n");
+
+    // close the file
+    close(file_descriptor);
+    exit(0);
+
+  } else {
+
+    // parent process
+
+    // read 5 characters from file into buf_parent
+    // print the characters in buf_parent to terminal
+    read(file_descriptor, buf_parent, 5);
+    printf("%s\n", buf_parent);
+
+    printf("pid= %d -- parent waits for child to terminate\n", pid);
+    printf("pid= %d -- before wait parent sees x= %lf, y=%lf\n", pid, x, y);
+
+    wait(&status); // note we are not catching the return value of wait!
+    printf("parent got termination status= %d from child\n", status);
+    printf("pid= %d -- after wait sees x= %lf, y=%lf\n", pid, x, y);
+
+    // read another 5 characters from file into buf_parent
+    // print the characters in buf_parent to terminal
+
+    // close the file
+    close(file_descriptor);
+    printf("parent is terminating\n");
+    exit(0);
+  }
+
+}
+
+pid_t Fork(void){
+  int pid = fork();
+  if (-1 == pid){
+     perror("fork() Failure\n");
+     exit(-1);
+  }
+}