In C, which of the following small programs best implements a simplified version of the DOS type command that prints the contents of a text file specified on the command line to standard output?

Introduction / Context:
The DOS type command reads a text file and writes its contents directly to the console. Implementing a similar command in C involves basic file handling and I O functions. This question checks whether you can identify the program that correctly opens a file given as a command line argument, handles errors and copies all characters from the file to standard output until end of file is reached.

Given Data / Assumptions:

• The user should run the program as type filename.
• The program should open the file specified by argv[1] for reading.
• If the file cannot be opened, an error message should be printed.
• If successful, the program should copy every character from the file to stdout.

Concept / Approach:
A minimal yet robust implementation needs to check the argument count, open the file in text read mode, loop reading single characters with fgetc and immediately write them with putchar until fgetc returns EOF. After the loop finishes, the code should close the file and return an appropriate status code. Additional niceties include printing a usage message when the user forgets to supply a filename and using perror to display the reason for failure when fopen fails.

Step-by-Step Solution:
Step 1: Confirm that the chosen program checks argc and prints a usage message if the user does not supply exactly one filename argument. Step 2: Ensure that it calls fopen(argv[1], "r"); to open the file in read mode. Step 3: Verify that it tests the result of fopen and prints an error via perror or a message if the open fails. Step 4: Check that the main loop reads characters with fgetc and writes them directly with putchar until EOF is reached. Step 5: Confirm that the file is closed with fclose(fp); and that main returns a reasonable status code.

Verification / Alternative check:
If you run the correct program on a sample text file, you will see that the console output matches the file contents exactly, including newlines. Testing error paths, such as invoking the program with no arguments or a non existent file, shows that it prints a usage message or a perror based message respectively. This behaviour matches what a simplified type command should do.

Why Other Options Are Wrong:
Option B reads a line from standard input using gets, which is unsafe and does not read from a file at all. Option C simply prints argv[1] as a string, which is the filename itself, not the contents of that file. Option D opens a hard coded file but does not read from it, prints nothing and lacks any argument handling, so it does not behave like a type command.

Common Pitfalls:
Programmers sometimes forget to check the return value of fopen, leading to undefined behaviour when trying to read from a null FILE pointer. Another pitfall is to assume that reading lines with fgets is necessary, when reading character by character is adequate for a simple copy utility. It is also easy to forget to close the file, which is not critical in a short lived program but is good practice and important in long running tools.

Final Answer:
The correct implementation is the program that checks argc, opens argv[1] with fopen, copies all characters from the file to stdout using fgetc and putchar, handles errors and then closes the file.