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How can I call a function with an argument list built up at run time?
How can I call a function with an argument list built up at run time? There is no guaranteed or portable way to do this. Instead of an actual argument list, you might consider passing an array of generic (void *) pointers. The called function can then step through the array, much like main() might s...
2015-06-03, 845👍, 0💬

Why is this loop always executing once?
Why is this loop always executing once? for(i = start; i &lt; end; i++); { printf("%d\n", i); } A: The accidental extra semicolon hiding at the end of the line containing the for constitutes a null statement which is, as far as the compiler is concerned, the loop body. The following brace-enclos...
2015-06-03, 792👍, 0💬

I am getting baffling syntax errors which make no sense at all
I'm getting baffling syntax errors which make no sense at all, and it seems like large chunks of my program aren't being compiled. Check for unclosed comments, mismatched #if/#ifdef/#ifndef/#else/#endi fdirectives, and perhaps unclosed quotes; remember to check header files, too.
2015-06-01, 766👍, 0💬

Why isnt my procedure call working? The compiler seems to skip right over it
Why isnt my procedure call working? The compiler seems to skip right over it Does the code look like this? myprocedure; C has only functions, and function calls always require parenthesized argument lists, even if empty. Use myprocedure(); Without the parentheses, the reference to the function name ...
2015-06-01, 760👍, 0💬

This program crashes before it even runs!
This program crashes before it even runs! (When single-stepping with a debugger, it dies before the first statement in main.) You probably have one or more very large (kilobyte or more) local arrays. Many systems have fixed-size stacks, and even those which perform dynamic stack allocation automatic...
2015-05-29, 798👍, 0💬

I have a program that seems to run correctly
I have a program that seems to run correctly, but it crashes as it's exiting, after the last statement in main(). What could be causing this? A:There are at least three things to look for: 1. If a semicolon in a previous declaration is missing, main might be inadvertently declared as returning a str...
2015-05-29, 776👍, 0💬

This program runs perfectly on one machine ...
This program runs perfectly on one machine, but I get weird results on another. Stranger still, adding or removing a debugging printout changes the symptoms... Lots of things could be going wrong; here are a few of the more common things to check: * uninitialized local variables integer overflow, es...
2015-05-27, 799👍, 0💬

Why does this code crash?
Why does this code: char *p = "hello, world!"; p[0] = 'H'; crash? String constants are in fact constant. The compiler may place them in nonwritable storage, and it is therefore not safe to modify them. When you need writable strings, you must allocate writable memory for them, either by declaring an...
2015-05-27, 789👍, 0💬

I have seen function declarations that look like this
I've seen function declarations that look like this: extern int func __((int, int)); What are those extra parentheses and underscores for? They're part of a trick which allows the prototype part of the function declaration to be turned off for a pre-ANSI compiler. Somewhere else is a conditional def...
2015-05-23, 962👍, 0💬

I have got some code that is trying to unpack external structures
I've got some code that's trying to unpack external structures, but it's crashing with a message about an ``unaligned access.'' What does this mean? The code looks like this: struct mystruct { char c; long int i32; int i16; } s; char buf[7], *p; fread(buf, 7, 1, fp); p = buf; s.c = *p++; s.i32 = *(l...
2015-05-20, 813👍, 0💬

What do Segmentation violation, `Bus error, and General protection fault mean? What is a core dump?
What do Segmentation violation, `Bus error, and General protection fault mean? What is a core dump? These symptoms (and any similar messages having to do with memory access violations or protection faults) generally mean that your program tried to access memory it shouldn't have, invariably as a res...
2015-05-20, 806👍, 0💬

What is the best style for code layout in C?
What is the best style for code layout in C? While providing the example most often copied, also supply a good excuse for disregarding it: The position of braces is less important, although people hold passionate beliefs. We have chosen one of several popular styles. Pick a style that suits you, the...
2015-05-18, 790👍, 0💬

How should functions be apportioned among source files?
How should functions be apportioned among source files? Usually, related functions are put together in one file. Sometimes (as when developing libraries) it is appropriate to have exactly one source file (and, consequently, one object module) per independent function. Other times, and especially for...
2015-05-18, 760👍, 0💬

Here is a neat trick for checking whether two strings are equal
Q: Here's a neat trick for checking whether two strings are equal: if(!strcmp(s1, s2)) Is this good style? It is not particularly good style, although it is a popular idiom. The test succeeds if the two strings are equal, but the use of ! (``not'') suggests that it tests for inequality. Another opti...
2015-05-15, 831👍, 0💬

Why do some people write if(0 == x) instead of if(x == 0)?
Why do some people write if(0 == x) instead of if(x == 0)? It's a trick to guard against the common error of writing if(x = 0) If you're in the habit of writing the constant before the ==, the compiler will complain if you accidentally type if(0 = x) Evidently it can be easier for some people to rem...
2015-05-15, 779👍, 0💬

I came across some code that puts a (void) cast before each call to printf. Why?
I came across some code that puts a (void) cast before each call to printf. Why? printf does return a value (the number of characters printed, or an error code), though few programs bother to check the return values from each call. Since some compilers (and lint) will warn about discarded return val...
2015-05-13, 809👍, 0💬

If NULL and 0 are equivalent as null pointer constants, which should I use?
If NULL and 0 are equivalent as null pointer constants, which should I use? Many programmers believe that NULL should be used in all pointer contexts, as a reminder that the value is to be thought of as a pointer. Others feel that the confusion surrounding NULL and 0 is only compounded by hiding 0 b...
2015-05-11, 834👍, 0💬

Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0?
Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0? It's your choice. Preprocessor macros like TRUE and FALSE (and, of course, NULL) are used for code readability, not because the underlying values might ever change. It's a matter of style, not correctness, wheth...
2015-05-11, 773👍, 0💬

What is Hungarian Notation? Is it worthwhile?
What is Hungarian Notation? Is it worthwhile? Hungarian Notation is a naming convention, invented by Charles Simonyi, which encodes information about a variable's type (and perhaps its intended use) in its name. It is well-loved in some circles and roundly castigated in others. Its chief advantage i...
2015-05-08, 833👍, 0💬

Some people say that gotos are evil and that I should never use them. Isnt that a bit extreme
Some people say that gotos are evil and that I should never use them. Isnt that a bit extreme rogramming style, like writing style, is somewhat of an art and cannot be codified by inflexible rules, although discussions about style often seem to center exclusively around such rules. In the case of th...
2015-05-08, 779👍, 0💬

People always say that good style is important
People always say that good style is important, but when they go out of their way to use clear techniques and make their programs readable, they seem to end up with less efficient programs. Since efficiency is so important, isn't it necessary to sacrifice some style and readability? It's true that g...
2015-05-06, 782👍, 0💬

I just typed in this program, and it is acting strangely. Can you see anything wrong with it?
I just typed in this program, and it is acting strangely. Can you see anything wrong with it? See if you can run lint first (perhaps with the -a, -c, -h, -p or other options ). Many C compilers are really only half-compilers, taking the attitude that it's not their problem if you didn't say what you...
2015-05-06, 775👍, 0💬

How can I shut off the warning ...
How can I shut off the ``warning: possible pointer alignment problem'' message which lint gives me for each call to malloc? A modern lint shouldn't be complaining about this. Once upon a time, lint did not and could not know that malloc ``returns a pointer to space suitably aligned for storage of an...
2015-05-05, 778👍, 0💬

Where can I get an ANSI-compatible lint?
Where can I get an ANSI-compatible lint? Products called PC-Lint and FlexeLint are available from Gimpel Software. The Unix System V release 4 lint is ANSI-compatible, and is available separately (bundled with other C tools) from UNIX Support Labs or from System V resellers. Another ANSI-compatible ...
2015-05-05, 850👍, 0💬

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