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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, 1629👍, 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, 1629👍, 0💬

How can I invoke another program (a standalone executable, or an operating system command) from within a C program?
How can I invoke another program (a standalone executable, or an operating system command) from within a C program? Use the library function system, which does exactly that. Some systems also provide a family of spawn routines which accomplish approximately the same thing. system is more ``portable'... 2015-03-18, 1629👍, 0💬

If fflush wont work, what can I use to flush input?
If fflush wont work, what can I use to flush input? It depends on what you're trying to do. If you're trying to get rid of an unread newline or other unexpected input after calling scanf you really need to rewrite or replace the call to scanf. Alternatively, you can consume the rest of a partially-r... 2015-10-12, 1627👍, 0💬

I think somethings wrong with my compiler ...
I think something's wrong with my compiler: I just noticed that sizeof('a') is 2, not 1 (i.e. not sizeof(char)). Perhaps surprisingly, character constants in C are of type int, so sizeof('a') is sizeof(int) (though this is another area where C++ differs). 2016-03-04, 1625👍, 0💬

How can I get random integers in a certain range?
How can I get random integers in a certain range? The obvious way, rand() % N /* POOR */ (which tries to return numbers from 0 to N-1) is poor, because the low-order bits of many random number generators are distressingly non-random. A better method is something like (int)((double)rand() / ((double)... 2015-07-29, 1624👍, 0💬

How can I suppress the dreaded MS-DOS Abort, Retry, Ignore? message?
How can I suppress the dreaded MS-DOS Abort, Retry, Ignore? message? Among other things, you need to intercept the DOS Critical Error Interrupt, interrupt 24H. See the comp.os.msdos.programmer 2015-04-06, 1623👍, 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, 1619👍, 0💬

What does it mean when the linker says that _end is undefined?
What does it mean when the linker says that _end is undefined? That message is a quirk of the old Unix linkers. You get an error about _end being undefined only when other symbols are undefined, too--fix the others, and the error about _end will disappear. 2015-07-06, 1618👍, 0💬

I have a varargs function which accepts a float parameter
I have a varargs function which accepts a float parameter. Why isn't va_arg(argp, float) working? In the variable-length part of variable-length argument lists, the old ``default argument promotions'' apply: arguments of type float are always promoted (widened) to type double, and types char and sho... 2015-06-08, 1618👍, 0💬

I need a sort of an approximate strcmp routine ...
I need a sort of an approximate strcmp routine ... Q: I need a sort of an ``approximate'' strcmp routine, for comparing two strings for close, but not necessarily exact, equality. A:Some nice information and algorithms having to do with approximate string matching, as well as a useful bibliography, ... 2015-01-09, 1618👍, 0💬

How can I read/write structures from/to data files?
How can I read/write structures from/to data files? It is relatively straightforward to write a structure out using fwrite: fwrite(&amp;somestruct, sizeof somestruct, 1, fp); and a corresponding fread invocation can read it back in. What happens here is that fwrite receives a pointer to the stru... 2015-09-18, 1617👍, 0💬

How do I create a directory? How do I remove a directory (and its contents)?
How do I create a directory? How do I remove a directory (and its contents)? If your operating system supports these services, they are likely to be provided in C via functions named mkdir and rmdir. Removing a directory's contents as well will require listing them and calling remove . If you don't ... 2015-04-01, 1617👍, 0💬

I am trying to define a few simple little function-like macros ...
I'm trying to define a few simple little function-like macros such as #define square(x) x * x but they're not always working. There are three important rules to remember when defining function-like macros: 1. The macro expansion must always be parenthesized to protect any lower-precedence operators ... 2016-02-26, 1616👍, 0💬

How can I swap two values without using a temporary?
How can I swap two values without using a temporary? The standard hoary old assembly language programmer's trick is: a ^= b; b ^= a; a ^= b; But this sort of code has little place in modern, HLL programming. Temporary variables are essentially free, and the idiomatic code using three assignments, na... 2015-02-06, 1612👍, 0💬

I have got this tricky preprocessing I want to do and I cant figure out a way to do it.
I have got this tricky preprocessing I want to do and I cant figure out a way to do it. C's preprocessor is not intended as a general-purpose tool. (Note also that it is not guaranteed to be available as a separate program.) Rather than forcing it to do something inappropriate, you might want to wri... 2016-01-19, 1611👍, 0💬

How can my program discover the complete pathname to the executable from which it was invoked?
How can my program discover the complete pathname to the executable from which it was invoked? argv[0] may contain all or part of the pathname, or it may contain nothing. You may be able to duplicate the command language interpreter's search path logic to locate the executable if the name in argv[0]... 2015-03-13, 1606👍, 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, 1605👍, 0💬

How can I flush pending input so that a user ...
How can I flush pending input so that a user's typeahead isn't read at the next prompt? Will fflush(stdin) work? fflush is defined only for output streams. Since its definition of ``flush'' is to complete the writing of buffered characters (not to discard them), discarding unread input would not be ... 2015-10-12, 1601👍, 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, 1601👍, 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, 1600👍, 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, 1600👍, 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, 1599👍, 0💬

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, 1599👍, 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