Back in May, I wondered how command line input could be processed when a wildcard is present (Lesson link). My research lead me to the glob() function, but you don’t use this function to process a command line wildcard argument. The reason is that these wildcards are handled by the shell; your code has no direct way to determine when a wildcard is present as a command line argument.
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From the history of the Unix operating system, glob is the term used for wildcard matching in filenames. It’s short for global, which to me means that two extra bytes of storage (for 'a' and 'l') were important back in the day.
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Wildcards were highly useful during the glory days of text mode operating systems. They still exist: ? represents a single character in a filename and * represents a group of characters. Using wildcards to manipulate files is a staple of computer file management, perhaps a lost art in the era of graphical operating systems, but still relevant. The C language is also still relevant, so how does it deal with wildcards in a filename?
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Unlike the iffy issue with assigning a pointer directly to a string, you cannot declare a pointer and assign it an immediate value. This puzzle was presented in last week’s Lesson. No, to do things properly requires not a single statement but three separate steps.
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I’m delighted to receive reader email regarding the various puzzles in the C programming language. Some of them involve creative thinking and approaches that seem like they work — but don’t. Pointers are one of the most common subjects.
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The C11 standard added the “underscore” bunch to the C language’s traditional keywords:
_Alignas
_Alingof
_Atomic
_Bool
_Complex
_Generic
_Imaginary
_Noreturn
_Static_assert
_Thread_local
I don’t routinely use any of these in my programs, beyond trying a few out to see how they work. The _Bool keyword comes in handy. The rest? Well, they’re worth exploring from a curiosity standpoint. For this week’s Lesson, I reveal the mysteries of the _Generic keyword.
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My approach for initializing a buffer is to use a loop and assign each byte a value such as zero or the null character, '\0'. It’s tedious, but necessary. And for the impatient, some functions are available to perform this task for you.
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When my code requires a random odd buffer, I generally assign it a given size in some holy computer value: 16, 32, 64, and so on. But a defined constant exists, BUFSIZ, that can also be used to set a buffer size safely and consistently on all C compilers.
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The defined constant NULL represents a null or empty pointer. I’ve written before that the constant isn’t defined as zero, though such an assumption could lead you into trouble.
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Mathematicians truly enjoy doing their math thing. As a mortal human, I don’t have a spot for math things on my “fun” spectrum. Yet, one of the more jolly things the math nerds do is discuss the value zero.
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