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How can I trap or ignore keyboard interrupts like control-C?
How can I trap or ignore keyboard interrupts like control-C? The basic step is to call signal, either as #include &lt;signal.h> signal(SIGINT, SIG_IGN); to ignore the interrupt signal, or as extern void func(int); signal(SIGINT, func); to cause control to transfer to function func on receipt of ... 2015-03-06, 1484👍, 0💬

I have a pre-ANSI compiler, without stdarg.h What can I do?
I have a pre-ANSI compiler, without stdarg.h What can I do? There's an older header, &lt;varargs.h>, which offers about the same functionality. Here is the vstrcat function, rewritten to use &lt;varargs.h>: #include &lt;stdio.h> #include &lt;varargs.h> #include &lt;string.h> exte... 2015-06-10, 1483👍, 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, 1483👍, 0💬

What are pragmas and what are they good for?
What are pragmas and what are they good for? The #pragma directive provides a single, well-defined ``escape hatch'' which can be used for all sorts of (nonportable) implementation-specific controls and extensions: source listing control, structure packing, warning suppression (like lint's old /* NOT... 2015-12-11, 1479👍, 0💬

My compiler is complaining that printf is undefined ...
My compiler is complaining that printf is undefined! How can this be? It's the world's most popular C function... Allegedly, there are C compilers for Microsoft Windows which do n ot support printf, on the argument that printf is for printing to old-fashioned terminals, while under Windows the right... 2015-07-03, 1476👍, 0💬

I am using scanf c to read a Y/N response
I'm using scanf %c to read a Y/N response, but later input gets skipped. You wanted scanf %c to read a single character, and it tried to, but when you tried to type that single character at it, before the rest of the input system would accept it, you had to hit the RETURN key, too. scanf read only t... 2015-10-21, 1473👍, 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, 1472👍, 0💬

How can I do serial comm port I O?
How can I do serial (``comm'') port I/O? It's system-dependent. Under Unix, you typically open, read, and write a device file in /dev, and use the facilities of the terminal driver to adjust its characteristics.Under MS-DOS, you can use the predefined stream stdaux, or a special file like COM1, or s... 2015-04-22, 1472👍, 0💬

I am trying to take some square roots
I'm trying to take some square roots, and I've simplified the code down to main() { printf("%f\n", sqrt(144.)); } but I'm still getting crazy numbers. Make sure that you have #included &lt;math.h>, and correctly declared other functions returning double. (Another library function to be careful w... 2015-07-01, 1471👍, 0💬

Once I have used freopen, how can I get the original stdout (or stdin) back?
Once I have used freopen, how can I get the original stdout (or stdin) back? There isn't a good way. If you need to switch back, the best solution is not to have used freopen in the first place. Try using your own explicit output (or input) stream variable, which you can reassign at will, while leav... 2015-10-01, 1470👍, 0💬

Why isnt it being handled properly?
I'm reading strings typed by the user into an array, and then printing them out later. When the user types a sequence like \n, why isn't it being handled properly? Character sequences like \n are interpreted at compile time. When a backslash and an adjacent n appear in a character constant or string... 2015-08-24, 1469👍, 0💬

I had a frustrating problem which turned out to be caused by the line
I had a frustrating problem which turned out to be caused by the line printf("%d", n); where n was actually a long int. I thought that ANSI function prototypes were supposed to guard against argument type mismatches like this. When a function accepts a variable number of arguments, its prototype doe... 2015-06-15, 1468👍, 0💬

How can I access an I O board directly?
How can I access an I O board directly? At one level, at least, it's quite simple: you have a device register which is actually wired up so that the bits written to it get coverted to actual voltage levels in the real world that you can do interesting things with. In general, there are two ways to g... 2015-04-20, 1468👍, 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, 1466👍, 0💬

I am trying to compile this program
I'm trying to compile this program, but the compiler is complaining that ``union REGS'' is undefined, and the linker is complaining that int86 is undefined. Those have to do with MS-DOS interrupt programming. They don't exist on other systems. 2015-03-02, 1466👍, 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, 1465👍, 0💬

I thought I would check errno after a long string of printf calls ...
I thought I'd check errno after a long string of printf calls, to see if any of them had failed: errno = 0; printf("This\n"); printf("is\n"); printf("a\n"); printf("test.\n"); if(errno != 0) fprintf(stderr, "printf failed: %s\n", strerror(errno)); Why is it printing something strange like ``printf f... 2015-10-14, 1462👍, 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, 1461👍, 0💬

How can I make it pause before closing the program output window?
I'm compiling some test programs on a windows-based system, and the windows containing my program's output are closing so quickly after my program calls exit that I can't see the output. How can I make it pause before closing? After wondering why the author of your compiler's run-time system didn't ... 2015-04-24, 1460👍, 0💬

How can I allocate arrays or structures bigger than 64K?
How can I allocate arrays or structures bigger than 64K? A reasonable computer ought to give you transparent access to all available memory. If you're not so lucky, you'll either have to rethink your program's use of memory, or use various system-specific techniques. 64K is (still) a pretty big chun... 2015-03-30, 1460👍, 0💬

How can I read a binary data file properly?
How can I read a binary data file properly? I'm occasionally seeing 0x0a and 0x0d values getting garbled, and I seem to hit EOF prematurely if the data contains the value 0x1a. When you're reading a binary data file, you should specify "rb" mode when calling fopen, to make sure that text file transl... 2015-09-24, 1456👍, 0💬

How can I send mail from within a C program?
How can I send mail from within a C program? Under Unix, open a pipe to the mail program, or perhaps /usr/lib/sendmail. 2015-04-17, 1453👍, 0💬

How can I return multiple values from a function?
How can I return multiple values from a function? There are several ways of doing this. (These examples show hypothetical polar-to-rectangular coordinate conversion functions, which must return both an x and a y coordinate.) 1. Pass pointers to several locations which the function can fill in: #incl... 2015-02-25, 1453👍, 0💬

Why do all the lines end up containing copies of the last line?
I'm using fgets to read lines from a file into an array of pointers. Why do all the lines end up containing copies of the last line? You have only allocated memory for one line, linebuf. Each time you call fgets, the previous line is overwritten. fgets doesn't do any memory allocation: unless it rea... 2015-11-13, 1452👍, 0💬

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.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML