File Input and Output

In this lab you will gain experience with both basic file input and output involving characters and strings as well as binary objects.

Basic File Utilities

Catching File Errors

1. Download, review, and compile the program fopen-test.c from the reading.
   1. Run the program, trying to generate as many different error messages as you can.
   2. The list of possible error messages can be checked by running the following MathLAN terminal command:

      errno -l

      Identify at least two additional errors that might be related to an fopen failure.
   3. Change the fprintf call within the (stream == NULL) test to use a call to perror instead. Recompile and run the program to generate the associated error. How does the output change?
   4. The reading advised you that the error-reporting fprintf within the argc test should not be changed to a perror. Make that change anyhow, then recompile and run the program to generate the associated error. What output do you get? Explain why that output is sensible in this context. Verify your answer with the instructor or mentor.

Counting characters, words, and lines: wc

2. Like the command line utility, wc, write a small program called mywc.c using getc to count all the characters in a file whose name is given as a command line argument. The program simply prints how many letters, spaces, newlines, and other characters there are in the file.
   • Your program should report human readable errors and exit if the file cannot be opened for reading. (If you use example code from the reading, be sure you cite it appropriately.)
   • In order to to test for EOF correctly, the textbooks and manual pages remind us that getc returns an int, not a char
   • To distinguish between the end of file condition and a read error, your program should use the function ferror after getc returns EOF
   • If a read error occurred, your program should report a human-readable message and exit.
   • Remember to close the file when you are done reading from it.
3. Augment your mywc.c program so that it will also count and print how many words there are in the specified file.
   • In this program, consider a word to be any consecutive sequence of letters separated by white space. Thus, you can count a word by identifing an initial non-whitespace character and then skipping through any subsequent such characters until you read a whitespace character. You'd start a new word again once you read a non-space character.
   • The function isspace from <ctype.h> should prove helpful.
   • Test your code by verifying that it produces the same count as given by the default terminal utility wc.
4. Augment your mywc.c program so that it will also count and print how many lines there are in the specified file.

Concatenating files: cat

5. Write a small C program called mycat.c that reads all the text files whose names are given on the command line and prints their contents to stdout.
   • You will likely find the C library functions fgets and fputs (or puts) useful. Recall that, in contrast with scanf, fgets returns NULL when it encounters the end of the file or an error.
   • If any file cannot be opened for reading, your program should report human readable error and continue with the next file. (If you use example code, be sure you cite it appropriately.)
   • If a read error occurred, your program should report a human readable message to the standard error stream and continue with the next file.
   • Remember to close each file when you are done (even if there was a read error).

Binary I/O

6. Write a program that instructs the robot to take a picture and then writes the struct with the picture data to a file using fwrite.
7. Write a companion program that uses fread to read the binary data for a picture struct and then uses rDisplayPicture from the MyroC header to display the picture.