From last week’s Lesson, you saw an example of how different data types stored in a union can be beneficial. As both structures WORDREGS and BYTEREGS overlapped to reflect the data stored in an 8086 CPU, using a union to represent the data is both practical and economic. But such conditions are rare.
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Reading an analog clock is a skill that some kids need to master these days. Oh, I’m sure that eventually everyone figures it out. When I was a kid, digital clocks were rare. No, we all learned how to tell time by looking at a round disk with 12 numbers and a big hand and a little hand. If a second hand was available, well it was just more entertainment for the terminally bored child.
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Though it’s shunned today, using a union in your C code was common in the 1980s. Back then, compilers and IDEs such as Borland’s TurboC were customized for the MS-DOS operating system. Daring C programmers used the C language’s union keyword to access the system’s hardware directly. Scary.
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A C language keyword worthy of shunning is union. It joins goto as another keyword to avoid, but union is more in the realm of the deprecated gets() function in that it has a potential for dangerous exploits. So why not have some fun with it before the C Lords banish it from the language?
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Continuing from last week’s Lesson, I discovered that though the C language lets you create a Boolean array, the data is stored in char-sized integers and not true binary data. But there is a way to convert that Boolean area into binary data; it just takes some coding legerdemain.
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This month’s Exercise is about finding the limits, or how large a signed or unsigned char value can get before it flips over to negative or to zero. And the trick is performing this feat in your code without using the defined constants for a char data type available in the limits.h header file.
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As a programmer well-versed in Assembly Language, I’m all too familiar with the bits that populate a byte. At the low, low level you find plenty of tools to do bit manipulation. The C language has bitwise operators as well, which remains one of its advantages over the newer, trendier programming languages. So, how does all this fun activity cross over into the realm of the _Bool or bool data type in C?
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The C language comes with a variety of data types that hold integer (whole number) values. But each type is limited by its size. The issue is to ensure that whatever value the program is manipulating never exceeds the given size.
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One of the weaknesses of the C language when measured against the newer, trendier programming languages is that it lacks a Boolean type. That is, a variable that’s either one or zero. This issue was addressed with the C99 standard and its addition of the underscore _Bool data type. It’s furthered in the C23 standard with the (better) bool type as well as the true and false keywords available in just about every other programming language used today. It’s time for a deep dive into the binary pool of bool.
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Having two file descriptors available to access the same file might seem redundant. In a way it is. It’s like having two sets of keys to a car: Yes, one could be a backup, but it’s more common that two different people are using the same car. But first, an example is necessary.
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