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How can I sort a linked list?
How can I sort a linked list? Sometimes it's easier to keep the list in order as you build it (or perhaps to use a tree instead). Algorithms like insertion sort and merge sort lend themselves ideally to use with linked lists. If you want to use a standard library function, you can allocate a tempora... 2015-08-10, 1677👍, 0💬

How can I call system when parameters (filenames, etc.) of the executed command arent known until run time?
How can I call system when parameters (filenames, etc.) of the executed command arent known until run time? Just use sprintf (or perhaps strcpy and strcat) to build the command string in a buffer, then call system with that buffer. (Make sure the buffer is allocated with enough space; Here is a cont... 2015-03-18, 1676👍, 0💬

Does C have circular shift operators?
Does C have circular shift operators? No. (Part of the reason why is that the sizes of C's types aren't precisely defined----but a circular shift makes most sense when applied to a word of a particular known size.) You can implement a circular shift using two regular shifts and a bitwise OR: (x &... 2015-01-28, 1676👍, 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... 2016-02-29, 1672👍, 0💬

What is the right way to use errno?
What is the right way to use errno? In general, you should detect errors by checking return values, and use errno only to distinguish among the various causes of an error, such as ``File not found'' or ``Permission denied''. (Typically, you use perror or strerror to print these discriminating error ... 2015-02-23, 1672👍, 0💬

What is hashing?
What is hashing? Hashing is the process of mapping strings to integers, usually in a relatively small range. A ``hash function'' maps a string (or some other data structure) to a bounded number (the ``hash bucket'') which can more easily be used as an index in an array, or for performing repeated co... 2015-01-07, 1671👍, 0💬

Why isnt any of this standardized in C? Any real program has to do some of these things.
Why isnt any of this standardized in C? Any real program has to do some of these things. Actually, some standardization has occurred along the way. In the beginning, C did not have a standard library at all; programmers always had to ``roll their own'' utility routines. After several abortive attemp... 2015-02-27, 1670👍, 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, 1669👍, 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, 1669👍, 0💬

Why does everyone say not to use scanf? What should I use instead?
Why does everyone say not to use scanf? What should I use instead? scanf has a number of problems, its %s format has the same problem that gets() has --it's hard to guarantee that the receiving buffer won't overflow. More generally, scanf is designed for relatively structured, formatted input (its n... 2015-10-21, 1667👍, 0💬

Suggesting that there can be 62 seconds in a minute?
Suggesting that there can be 62 seconds in a minute? Q: Why can tm_sec in the tm structure range from 0 to 61, suggesting that there can be 62 seconds in a minute? A: That's actually a buglet in the Standard. There can be 61 seconds in a minute during a leap second. It's possible for there to be two... 2015-01-05, 1667👍, 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, 1666👍, 0💬

How can I add N days to a date? How can I find the difference between two dates?
How can I add N days to a date? How can I find the difference between two dates? The ANSI/ISO Standard C mktime and difftime functions provide some (limited) support for both problems. mktime accepts non-normalized dates, so it is straightforward to take a filled-in struct tm, add or subtract from t... 2015-08-05, 1664👍, 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, 1663👍, 0💬

Can you mix old-style and new-style function syntax?
Can you mix old-style and new-style function syntax? Doing so is legal (and can be useful for backwards compatibility), but requires a certain amount of care . Modern practice, however, is to use the prototyped form in both declarations and definitions. (The old-style syntax is marked as obsolescent... 2016-01-13, 1663👍, 0💬

How can I invoke another program or command and trap its output?
How can I invoke another program or command and trap its output? Unix and some other systems provide a popen function, which sets up a stdio stream on a pipe connected to the process running a command, so that the calling program can read the output (or alternatively supply the input). Using popen, ... 2015-03-16, 1661👍, 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, 1659👍, 0💬

How can I write a function which takes a variable number of arguments
How can I write a function which takes a variable number of arguments and passes them to some other function (which takes a variable number of arguments)? In general, you cannot. Ideally, you should provide a version of that other function which accepts a va_list pointer. Suppose you want to write a... 2015-06-05, 1659👍, 0💬

If the assignment operator were ...
If the assignment operator were :=, wouldn't it then be harder to accidentally write things like if(a = b) ? A: Yes, but it would also be just a little bit more cumbersome to type all of the assignment statements which a typical program contains. In any case, it's really too late to be worrying abou... 2015-01-26, 1657👍, 0💬

How can I automatically locate a programs configuration files in the same directory as the executable?
How can I automatically locate a programs configuration files in the same directory as the executable? It's hard, in general; Even if you can figure out a workable way to do it, you might want to consider making the program's auxiliary (library) directory configurable, perhaps with an environment va... 2015-03-13, 1656👍, 0💬

I have been replacing multiplications and divisions with shift operators, because shifting is more efficient.
I have been replacing multiplications and divisions with shift operators, because shifting is more efficient. This is an excellent example of a potentially risky and usually unnecessary optimization. Any compiler worthy of the name can replace a constant, power-of-two multiplication with a left shif... 2015-02-09, 1655👍, 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, 1654👍, 0💬

I am reading strings typed by the user into an array ...
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... 2016-03-04, 1654👍, 0💬

There seem to be a few missing operators ..
There seem to be a few missing operators, like ^^, &amp;&amp;=, and -&gt;=. A:A logical exclusive-or operator (hypothetically ``^^'') would be nice, but it couldn't possibly have short-circuiting behavior analogous to &amp;&amp; and || Similarly, it's not clear how short-circuiti... 2015-01-28, 1654👍, 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