Command line options often sport their own options or settings. For example, tab width might be set by specifying the tabwidth option followed by a value. No hard and fast rules exist for how such an option is set, but I’ve seen it happen in one of three ways:
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Your code must consider whether or not command line options are present, that the user may type the options in any order, and that some or all of the option could be incorrect. That makes for a lot of processing, but it’s also forgiving and users prefer the flexibility.
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When processing the main() function’s arguments, you must keep in mind the possibilities. Options are, after all, options. They might be there, they might not.
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About a year ago, I wrote a post on reading the command line arguments. It’s a process that takes place all the time, not only when running programs in a terminal window but also for graphical operating systems. Knowing how to manipulate command line arguments is important.
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I’ll confess that when I use a quicksort to sort and array of strings, I don’t use the C Library’s qsort() function. No, I write my own. The problem is that when sorting an array of strings, the qsort() function’s compar argument is a pain in the butt to craft properly.
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The quicksort deftly handles vast quantities of values. It can also sort strings, but that’s where things can get weird.
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The Internet is littered with plenty of good explanations of how the quicksort works. The definition at Wikipedia graphically illustrates the process, which is commonly called “divide and conquer.” I’ve stolen the Wikipedia illustration and placed it into Figure 1.
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Computers excel at searching and sorting. That, and they can occasionally screw up a phone bill.
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Computers are good at performing repetitive tasks; doing the same boring nonsense over and over. Two great examples are searching and sorting.
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In last week’s Lesson I mentioned the constant, MAXPATHLEN. Like PATH_MAX, it returns the size of the maximum number of characters allowed in a pathname. Unlike PATH_MAX, however, MAXPATHLEN is defined in the sys/param.h header file, not limits.h.
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