My first Unix System Administrator job was pretty routine: I did backups. It was only later that I discovered some of the many nerdy treasures available in that operating system.
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Finding the Dictionary
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Coin Flipping Madness!
Difficulty: ★ ★ ☆ ☆
Probability. Odds. These are words I often confuse, but the similarity relates to how often things happen. The gold standard is the flip of a coin: two possibilities, heads or tails. If you don’t understand how it works, you can write code to drive home the point.
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Using make to Build Projects
The make utility has been around since the early days of Unix. This tool is designed to create large projects by compiling and linking files based on dependencies. It takes care of a lot problems managing multi-module files to streamline the build process.
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Memory-File Multi-Module Implementation
At 205 lines of code in last week’s Lesson, my memory-file project is getting larger by the day. At some point, the source code files must be broken out into separate modules, then compiled and linked separately. This is how I handle all large projects when it becomes too unwieldly to edit everything in a single file.
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Enabling Random Memory-File Access
The two types of file access are sequential and random. Sequential access means the file’s data is read from beginning to end, one byte after the other. Random access isn’t random in the sense that it’s haphazard. No, random access means you can read data from any position in the file: beginning, middle, or end.
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Reading and Writing to Memory-Files
Opening and closing a memory-file is just academic. To make the whole shebang work, you must be able to read and write data.
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Finding Characters – Solution
The challenge for this month’s Exercise is to write the charcount() function, which returns the number of characters in a string. The character matches exactly, so don’t worry about checking uppercase and lowercase differences.
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Opening and Closing Memory-Files
To treat a chunk of memory as a file, it must be “opened” and a handle returned for future file reference and interaction. Likewise, the memory-file must be “closed” when you no longer need it. To accomplish these tasks, I’ve crafted the mem_open() and mem_close() functions.
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Finding Characters
Difficulty: ★ ★ ☆ ☆
When I was working on last month’s Exercise, I scoured the C library for a function that returned the number of specific characters found in a string. The closest I could find was strchr(), which returns the location of a given character in a string. You can set this function in a loop to find subsequent characters, but what I needed was a tally, a total count of all matching characters in the string.
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Memory Files
In the Unix environment, everything is a file. For example, you can open the terminal as a file, which I covered in a previous Lesson. But what about memory? Can you open memory as a file? And why would you want to?
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