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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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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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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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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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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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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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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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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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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With all the storage available in a modern computer, it’s easy — and often perfectly okay — to be overly generous when allocating memory. Still, the old coder in me has a lingering desire to save every byte possible. So when it comes to crafting a solution for this month’s Exercise, my desire is to be byte stingy.
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