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Learn how to effectively control the output of your C+ + program by using a Makefile and shell commands to print limited results from a text file.
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Controlling Output of Your C+ + Program Using Makefile

When it comes to programming, especially in C+ + , you may find yourself needing to control the output of your executables based on specific criteria. For example, let’s explore a scenario where you have a C+ + program print-word-length.cc that reads words from a file and prints their lengths. If you wish to modify its output to only print the first ten lengths of words from the dictionary text file, the typical approach could be slightly misleading. Let's break down this issue and find the solution together!

The Problem

You have a command that looks like this:

[[See Video to Reveal this Text or Code Snippet]]

This command gives you the lengths of words from the dictionary file but does not limit the output. You wanted to restrict it to just the first ten lengths, and tried using:

[[See Video to Reveal this Text or Code Snippet]]

However, this approach printed “gibberish” instead of the desired output. Why does this happen?

Understanding the Issue

Why the head Command Fails

The head utility is designed to read a file or input stream and return the first few lines of text. In your case, you were attempting to run your C+ + executable with head, which is likely resulting in reading the first lines of the binary executable file rather than the output generated by your program. This is why you see gibberish instead of meaningful data.

The Solution: Utilizing Pipes

To achieve what you want, you can use pipes in Unix-like systems. A pipe (|) allows you to take the output of one command and make it the input for another. Here's how you can modify your command correctly:

Correct Command Structure

Instead of using head to directly read from the binary executable, you should structure your command as follows:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Command

./print-word-length.cc < /dir/dictionary.txt: This runs your C+ + program, using input redirection to feed it data from dictionary.txt.

|: The pipe operator sends the output from the first command to the next.

head -n 10: This will take the first 10 lines of the output from your C+ + program and display them.

By using this command setup, you effectively limit the output to just the first ten lengths of words from your dictionary file without dealing with unexpected output.

Implementing in Makefile

Now that you have the correct shell command, you can incorporate this into your Makefile. Here’s an example target you can add:

[[See Video to Reveal this Text or Code Snippet]]

Running the Makefile

To execute this Makefile target, simply run:

[[See Video to Reveal this Text or Code Snippet]]

This command will invoke your program and limit the output as desired.

Conclusion

Controlling the output of your C+ + program for specific needs can be achieved seamlessly by combining shell commands with appropriate use of pipes. By understanding how utilities like head function and integrating this logic into your Makefile, you can significantly enhance the utility of your programs. Now you're well equipped to limit the output of your print-word-length.cc program effectively. Happy coding!