CIS105 Fall 2003 Lab09

Part One: Writing to files

cp ~pconrad/public_html/cis105/2003.fall/labs/lab12Code/lab12a.c .

/* a program that just demonstrates how to write output to a file */

#include <stdio.h>

int main ()
{
  FILE *outfile;  /* declare a file pointer */
  int x=3;        /* x and y are variables just for demonstration purposes */
  double y=4.5;
  
  /* open the output file */
  
  outfile = fopen("lab12a.dat","w"); /* try to open file for writing */
  if (outfile == NULL)               /* check return status */
    {
      perror("File lab12a.dat could not be opened: "); /* print error */
      exit(-1);
    }
  
  /* write some output to the file */
  
  fprintf(outfile,"This output is going to the file lab12a.dat.\n");
  
  printf("This output is going to the terminal.\n");
  printf("I can still write to the terminal in the same program\n");
  printf("that I am writing to a file.\n");
  
  fprintf(outfile,"I can also print the value of variables to a file.\n");
  fprintf(outfile,"for example, x=%d, y=%.2f\n",x,y);
  fprintf(outfile,"Bye now!\n");
  
  /* close the output file */
  
  fclose(outfile);
  
  return 0;
}

1. Copy the lab12a.c file into your directory.
2. Compile it, but don't run it yet.
3. Before you run it, do an ls command, and note that there is no file called lab12a.dat in your directory.
4. Now run the program. Note the output you get on your screen. Then do another ls command and note that there should now be a file called lab12a.dat in your directory. Use cat lab12a.dat to list the output of this file.
5. Now edit the lab12a.c file to personalize the message that is going to the file. Make it print your name to the file as part of the message, along with any other pithy comments you want to pass along to your TA and/or instructor.
6. Use the rm command to delete lab12.dat from your directory. Then, make a script file lab12a.txt in which you
   1. cat and then compile your new (personalized) version of lab12a.c,
   2. use ls to show that there is no lab12a.dat file in your directory,
   3. run the program,
   4. redo the ls command to show that lab12a.dat was created,
   5. and cat the output of your new personalized lab12a.dat.
   
   You should submit lab12a.txt as part of your submission for lab12. You don't need to submit the .c file, or the .dat file for this part.

Part Two: Writing to multiple files

To do this part of the lab, take the following steps.

1. Copy this file (lab12b.c) into your directory. The form of the command is the same as the command for lab12a.c.
2. Look over the program and try to understand how it works.
3. Run the program and observe the two new files that are created in your directory. As with lab12a.c, you should do an ls command before and after you run the program to see what files are created. Use cat or more to see the contents of the files.
4. Use the command gnuplot lab12b.gnuplot to generate a file lab12b.png. Then, view the file, either by copying it into your public_html directory and using a web browser to view it, or, if you are on an X terminal, using the command xv lab12b.png.
5. Note that the letter S is missing a piece. Make the necessary changes to the program to fix this.
6. When you are finished, cat and script your completed program. Your script should include a cat of the resulting files lab12b.dat and lab12b.gnuplot(though NOT the .png file, which you should NOT cat, since it will just fill the script file with garbage). Use lab12b.txt as the name of your script.
7. As a final step, make a subdirectory called cis105 in your public_html directory (i.e. mkdir ~/public_html/cis105). Copy your lab12b.png file into that subdirectory. Make both the subdirectory and the file world readable, so that the URL http://udel.edu/~youruserid/cis105/lab12b.png allows anyone who wants to (e.g. me and your TA) to see your resulting output file.

For an A grade: