They’re the orphan keywords, urchins, unwanted, unused, unloved. Of the 32 C language keywords, a handful are seldom used. These include: auto, enum, register, union, and volatile.
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All of the code I’ve written in my books as well as demonstrated on this blog has been single-tasking: The program runs as one process, does one thing, in order, and then terminates. With this Lesson, that streak ends.
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Program. Software. Application. Process. These are all terms that describe different aspects of a similar thing.
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To launch and run another program from within your code, use the system() function. When your code must examine or save that program’s output, use the popen() function.
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The system() function allows you to run one program from within another. If it’s your desire to launch another program and have your program quit, you can immediately follow system() with an exit() function. Or you can go out of your way and use the oddball execl() function.
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Suppose that you’re testing code and need to run a program six times in a row. You could keep repeating the program, running it multiple times, but why not write a utility that does the same thing? That would be a good and practical way to put the system() function to work.
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One thing that continues to puzzle me about learning the C language is how frequently beginners use the system() function. Is it a crutch? Is it a necessity? What’s the allure of this function that makes it show up in beginner code?
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The standard C library contains a lot of interesting and unusual routines. Some can really put the fun into function. One of them I’ve rarely used, but which can be extremely handy, is atexit().
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I was a bit surprised the other day. I’d written code on my Macintosh and tried to run it on the PC. Because I usually write generic stuff, I figured that the code would compile and run on both systems. But it didn’t compile.
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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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