• Each should compile successfully when compiled with the -Wall and -Werror flags.
• Each should (hopefully) pass the tests we will discuss.

wcat

The program wcat is a simple program. Generally, it reads a file as specified by the user and prints its contents. A typical usage is as follows, in which the user wants to see the contents of main.c, and thus types:

prompt> ./wcat main.c

#include

...

As shown, wcat reads the file main.c and prints out its contents. The "./" before the wcat above is a UNIX thing; it just tells the system which directory to find wcat in (in this case, in the "." (dot) directory, which means the current working directory).

To create the wcat binary, you'll be creating a single source file, wcat.c, and writing a little C code to implement this simplified version of cat. To compile this program, you will do the following:

prompt> gcc -o wcat wcat.c -Wall -Werror

prompt>

This will make a single executable binary called wcat which you can then run as above.

You'll need to learn how to use a few library routines from the C standard library (often called libc) to implement the source code for this program, which we'll assume is in a file called wcat.c. All C code is automatically linked with the C library, which is full of useful functions you can call to implement your program. Learn more about the C library here (Links to an external site.) and perhaps here (Links to an external site.)¹ (Links to an external site.).

For this project, we recommend using the following routines to do file input and output: fopen(), fgets(), and fclose(). Whenever you use a new function like this, the first thing you should do is read about it -- how else will you learn to use it properly?

On UNIX systems, the best way to read about such functions is to use what are called the man pages (short for manual). In our HTML/web-driven world, the man pages feel a bit antiquated, but they are useful and informative and generally quite easy to use.

To access the man page for fopen(), for example, just type the following at your UNIX shell prompt:

prompt> man fopen

Then, read! Reading man pages effectively takes practice; why not start learning now?

We will also give a simple overview here. The fopen() function "opens" a file, which is a common way in UNIX systems to begin the process of file access. In this case, opening a file just gives you back a pointer to a structure of type FILE, which can then be passed to other routines to read, write, etc.

Here is a typical usage of fopen():

FILE *fp = fopen("main.c", "r");

if (fp == NULL) {

printf("cannot open file ");

exit(1);

}

A couple of points here. First, note that fopen() takes two arguments: the name of the file and the mode. The latter just indicates what we plan to do with the file. In this case, because we wish to read the file, we pass "r" as the second argument. Read the man pages to see what other options are available.

Second, note the critical checking of whether the fopen() actually succeeded. This is not Java where an exception will be thrown when things goes wrong; rather, it is C, and it is expected (in good programs, i.e., the only kind you'd want to write) that you always will check if the call succeeded. Reading the man page tells you the details of what is returned when an error is encountered; in this case, the macOS man page says:

Upon successful completion fopen(), fdopen(), freopen() and fmemopen() return

a FILE pointer. Otherwise, NULL is returned and the global variable errno is

set to indicate the error.

Thus, as the code above does, please check that fopen() does not return NULL before trying to use the FILE pointer it returns.

Third, note that when the error case occurs, the program prints a message and then exits with error status of 1. In UNIX systems, it is traditional to return 0 upon success, and non-zero upon failure. Here, we will use 1 to indicate failure.

Side note: if fopen() does fail, there are many reasons possible as to why. You can use the functions perror() or strerror() to print out more about why the error occurred; learn about those on your own (using ... you guessed it ... the man pages!).

Once a file is open, there are many different ways to read from it. The one we're suggesting here to you is fgets(), which is used to get input from files, one line at a time.

To print out file contents, just use printf(). For example, after reading in a line with fgets() into a variable buffer, you can just print out the buffer as follows:

printf("%s", buffer);

Note that you should not add a newline ( ) character to the printf(), because that would be changing the output of the file to have extra newlines. Just print the exact contents of the read-in buffer (which, of course, many include a newline).

Finally, when you are done reading and printing, use fclose() to close the file (thus indicating you no longer need to read from it).

Details

• Your program wcat can be invoked with one or more files on the command line; it should just print out each file in turn.
• In all non-error cases, wcat should exit with status code 0, usually by returning a 0 from main() (or by calling exit(0)).
• If no files are specified on the command line, wcat should just exit and return 0. Note that this is slightly different than the behavior of normal UNIX cat (if you'd like to, figure out the difference).
• If the program tries to fopen() a file and fails, it should print the exact message "wcat: cannot open file" (followed by a newline) and exit with status code 1. If multiple files are specified on the command line, the files should be printed out in order until the end of the file list is reached or an error opening a file is reached (at which point the error message is printed and wcat exits).

Wcat . Check the value of argc -> if no command line arguments were passed i.e., argc == 1), then simply exit. If there are command line arguments, iterate through each file name in argv[] use fopen() to open each file name in read mode use fgets or getline to read each line from the file print each line to stdout close the file before continuing the the next filename, if there is one Matthew Majoki C W Grep . Check the value of argc . If it is 1. exit with a status of 1 If it is 2. treat the first argument as the search term, and search using stdin instead of an open FILE . If it is > 2, treat the first argument as the search tearm, and treat the rest of the arguments as search files Iterate over each file like in wcat . read each line from the file using getline . Check if the line contains the search term using strstr() If it does, print the line Close the file before continuing to the next, if there is one Mam Maj