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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One of C library functions I find most odd is dup(). I pronounce this function as if it rhymes with cup. I assume others may pronounce it like doop, which rhymes with poop. Whatever. The key is what the function does and how it could even remotely be necessary.
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About six years ago, I wrote about opening a file in the raw. Specifically, using the open() function to access file data at a low level. This approach uses file descriptors (integers) to track file I/O as opposed to the file handles used by the high-level fopen() family of functions. It turns out that you can do more with raw file access than just read and write data.
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The for keyword opens the door to looping in C, as well as in other programming languages. When teaching this concept, I keep the for loop format simple. After all there’s a lot of cryptic stuff between those parenthesis. And — brace yourself — there’s room for a lot of other stuff as well.
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Anyone who’s programmed in C for a while has worked with other libraries. In Linux, it’s common to link in the math library, libm.a. Other libraries are available to expand what the C language can do. I have books available on Ncurses, curl, XML and JSON, each of which has a library that makes it easy to use these powerful utilities. But what about making your own library?
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As I plow the digital seas, I often come across a piece of programming flotsam worthy of investigation. Most of it is obfuscated C, which is delightful. The obfuscated code that outputs something wonderful is most entertaining. But every so often I stumble upon something perplexing like the following code:
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When I first learned Assembly Language, I had a fear of blowing up the stack. Remember, back in the 8-bit microcomputer era that memory space was tight, maybe only part of 64K. A stack would have 1K of storage, if that. I think the stack size on my TRS-80 was 256 bytes. (An address was only two bytes wide.) This limitation meant that pushing too much data on the stack would blow up the computer.
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Today is Independence Day in the USA. Two hundred and fifty years ago, this nation’s founding fathers signed the Declaration of Independence. While I’ve had posts dated July 4 previously on this blog, today is a special anniversary. It necessitates a specific C language program.
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The ctype isxdigit() function returns TRUE for any digit you find in a hexadecimal number. I suppose this function has a role to play, most likely in detecting hexadecimal characters in a string. Regardless, this post wraps up my exploration of the ctype functions.
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For the ctype ispunct() function, the goal is to understand that “punct” is short for punctuation and not puncture. To put this function to use you need to know what the library considers to be an ASCII punctuation character. It’s yet another step forward in my ongoing exploration of the ctype functions.
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