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How can I find out how much memory is available?
How can I find out how much memory is available? Your operating system may provide a routine which returns this information, but it's quite system-dependent. (Also, the number may vary over time.) If you're trying to predict whether you'll be able to allocate a certain amount of memory, just try it-... 2015-03-30, 1507👍, 0💬

I am checking a string to see if it matches a particular value...
I'm checking a string to see if it matches a particular value. Why isn't this code working? char *string; ... if(string == "value") { /* string matches "value" */ ... } Strings in C are represented as arrays of characters, and C never manipulates (assigns, compares, etc.) arrays as a whole. The == o... 2016-03-11, 1506👍, 0💬

I am appalled that the ANSI Standard leaves so many issues undefined ...
I'm appalled that the ANSI Standard leaves so many issues undefined. Isn't a Standard's whole job to standardize these things? It has always been a characteristic of C that certain constructs behaved in whatever way a particular compiler or a particular piece of hardware chose to implement them. Thi... 2015-11-18, 1506👍, 0💬

I am still getting errors due to library functions being undefined
I'm still getting errors due to library functions being undefined, even though I'm explicitly requesting the right libraries while linking. Many linkers make one pass over the list of object files and libraries you specify, and extract from libraries only those modules which satisfy references which... 2015-07-14, 1506👍, 0💬

How can I clear the screen? How can I print text in color? How can I move the cursor to a specific x, y position?
How can I clear the screen? How can I print text in color? How can I move the cursor to a specific x, y position? Such things depend on the terminal type (or display) you're using. You will have to use a library such as termcap, terminfo, or curses, or some system-specific routines, to perform these... 2015-04-27, 1506👍, 0💬

What is assert and when would I use it?
What is assert and when would I use it? It is a macro, defined in &lt;assert.h>, for testing ``assertions''. An assertion essentially documents an assumption being made by the programmer, an assumption which, if violated, would indicate a serious programming error. For example, a function which ... 2015-01-12, 1505👍, 0💬

I have some old code that tries to construct identifiers with a macro like ...
I have some old code that tries to construct identifiers with a macro like #define Paste(a, b) a/**/b but it doesn't work any more. It was an undocumented feature of some early preprocessor implementations (notably Reiser's) that comments disappeared entirely and could therefore be used for token pa... 2016-01-27, 1499👍, 0💬

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, 1498👍, 0💬

Why doesn't sizeof tell me the size of the block of memory pointed to by a pointer?
Why doesn't sizeof tell me the size of the block of memory pointed to by a pointer? sizeof tells you the size of the pointer. There is no portable way to find out the size of a malloc'ed block. (Remember, too, that sizeof operates at compile time 2016-03-21, 1496👍, 0💬

What if a built-in logical or relational operator `returns something other than 1? ....
Isn't #defining TRUE to be 1 dangerous, since any nonzero value is considered ``true'' in C? What if a built-in logical or relational operator ``returns'' something other than 1? It is true (sic) that any nonzero value is considered true in C, but this applies only ``on input'', i.e. where a Boolean... 2016-02-29, 1495👍, 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, 1495👍, 0💬

Can I use base-2 constants (something like 0b101010)? Is there a printf format for binary?
Can I use base-2 constants (something like 0b101010)? Is there a printf format for binary? No, on both counts, although there are various preprocessor tricks you can try. You can convert base-2 string representations to integers with strtol. If you need to print numbers out in base 2, . 2015-02-13, 1495👍, 0💬

People keep saying that the behavior of ...
People keep saying that the behavior of i = i++ is undefined, but I just tried it on an ANSI-conforming compiler, and got the results I expected. A compiler may do anything it likes when faced with undefined behavior (and, within limits, with implementation-defined and unspecified behavior), includi... 2015-11-18, 1494👍, 0💬

How can I read a directory in a C program?
How can I read a directory in a C program? See if you can use the opendir and readdir functions, which are part of the POSIX standard and are available on most Unix variants. Implementations also exist for MS-DOS, VMS, and other systems. (MS-DOS also has FINDFIRST and FINDNEXT routines which do esse... 2015-04-01, 1493👍, 0💬

What is the difference between ...
What's the difference between const MAXSIZE = 100; and #define MAXSIZE 100 A preprocessor #define gives you a true compile-time constant. In C, const gives you a run-time object which you're not supposed to try to modify; ``const'' really means ``readonly''. 2016-02-18, 1492👍, 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, 1492👍, 0💬

I need some code to do regular expression and wildcard matching.
I need some code to do regular expression and wildcard matching. Make sure you recognize the difference between: * Classic regular expressions, variants of which are used in such Unix utilities as ed and grep. In regular expressions, a dot . usually matches any single character, and the sequence .* ... 2015-08-12, 1490👍, 0💬

Is C a great language, or what?
Is C a great language, or what? Where else could you write something like a+++++b ? A: Well, you can't meaningfully write it in C, either. The rule for lexical analysis is that at each point during a straightforward left-to-right scan, the longest possible token is determined, without regard to whet... 2015-01-26, 1489👍, 0💬

What's the difference between using a typedef or a define for a user-defined type?
What's the difference between using a typedef or a define for a user-defined type? In general, typedefs are preferred, in part because they can correctly encode pointer types. For example, consider these declarations: typedef char *String_t; #define String_d char * String_t s1, s2; String_d s3, s4; ... 2016-02-22, 1488👍, 0💬

I heard that you have to include ......
I heard that you have to #include before calling printf. Why? So that a proper prototype for printf will be in scope. A compiler may use a different calling sequence for functions which accept variable-length argument lists. (It might do so if calls using variable-length argument lists were less eff... 2016-01-08, 1488👍, 0💬

What are the complete rules for header file searching?
What are the complete rules for header file searching? The exact behavior is implementation-defined (which means that it is supposed to be documented; Typically, headers named with &lt;> syntax are searched for in one or more standard places. Header files named with "" syntax are first searched ... 2016-02-12, 1487👍, 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, 1487👍, 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, 1487👍, 0💬

Why cant I perform arithmetic on a void pointer?
Why cant I perform arithmetic on a void pointer? The compiler doesn't know the size of the pointed-to objects. (Remember that pointer arithmetic is always in terms of the pointed-to size; Therefore, arithmetic on void *'s is disallowed (though some compilers allow it as an extension). Before perform... 2015-12-07, 1486👍, 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