In last week’s Lesson, I covered the ftell() function, which returns the current file position indicator. That indicator can be manipulated, allowing you to control how a file is read in a non-sequential way.
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Like reading a book, sequential file access starts at the file’s beginning (or top) and reads bytes one after the other until the nefarious EOF is encountered. You probably don’t think about how that works, and you don’t need to. The operating system handles the job of reading a file; your C code is simply along for the ride.
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Say you have a for loop that increments one notch each time it repeats. I code such a loop in this fashion:
for(x=0;x<10;x++)More common, however, programmers use this approach:
for(x=0;x<10;++x)The difference is in how the variable x is incremented. I put the ++ after the x, but most coders put it before. What the deal?
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For my solution to this month’s Exercise I went binary. Several of the C language operators work at a binary level. Because the exercise was to make a binary, or bitwise, modification, I figured a binary operator would be in order.
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Of the two C language keyword looping statements, for is the most traditional and probably the most popular. It’s also the most frustrating for beginners because of its many parts. But eventually, a comfort level arises with using the for loop, which is sad because it’s more powerful than a simple counter.
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All the nonsense that takes place in programming happens because it’s possible to change the value of a bit from 0 to 1 and back again. The general concept is known as a toggle switch: The item can be set and reset between on and off positions.
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You could call it a neat trick or just something so oddball insane that few programmers would dare breech the territory: A variable that holds the address of a function; a function pointer.
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Like a variable in the C language, a function has an address — a location in memory. This fact shouldn’t be surprising to you. After all, the function has to sit somewhere. And my guess is that location doesn’t change as the program runs.
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The C language holds the potential of being utterly terrifying, which is something I admire greatly. Many beginners, as well as foolhardy travelers from other languages, treat a lot of the C language constructs as absolutes when, in fact, they aren’t. Therefore I present this week’s Lesson, the first in an ongoing series about strange, beautiful, and frightening things in the C language.
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The key to unlocking this month’s Exercise is not to go insane on the code that processes the solution. As I wrote in the Exercise post, with data analysis in C, it’s important to properly represent the data so that you can easily manipulate it.
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