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fopen isnt letting me open files like "$HOME/.profile" and "~/.myrcfile".
fopen isn't letting me open files like "$HOME/.profile" and "~/.myrcfile". Under Unix, at least, environment variables like $HOME, along with the home-directory notation involving the ~ character, are expanded by the shell, and there's no mechanism to perform these expansions automatically when you ... 2015-04-06, 1756👍, 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, 1753👍, 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, 1752👍, 0💬

Which of the following is the C# escape character for Null?
Which of the following is the C# escape character for Null? Which of the following is the C# escape character for Null? * \n * \0 * \f * \v \0 2014-08-06, 1750👍, 0💬

Is it acceptable for one header file to #include another?
Is it acceptable for one header file to #include another? It's a question of style, and thus receives considerable debate. Many people believe that ``nested #include files'' are to be avoided: the prestigious Indian Hill Style Guide disparages them; they can make it harder to find relevant definitio... 2016-02-16, 1748👍, 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, 1745👍, 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, 1744👍, 0💬

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, 1743👍, 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, 1742👍, 0💬

Are the outer parentheses in return statements really optional?
Are the outer parentheses in return statements really optional? Yes. Long ago, in the early days of C, they were required, and just enough people learned C then, and wrote code which is still in circulation, that the notion that they might still be required is widespread. (As it happens, parentheses... 2015-02-02, 1742👍, 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, 1741👍, 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, 1741👍, 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, 1739👍, 0💬

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, 1736👍, 0💬

Each time I run my program, I get the same sequence of numbers back from rand
Each time I run my program, I get the same sequence of numbers back from rand It's a characteristic of most pseudo-random number generators (and a defined property of the C library rand) that they always start with the same number and go through the same sequence. (Among other things, a bit of predi... 2015-07-29, 1735👍, 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, 1735👍, 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, 1733👍, 0💬

I inherited some code which contains far too many ...
I inherited some code which contains far too many #ifdef's for my taste. How can I preprocess the code to leave only one conditional compilation set, without running it through the preprocessor and expanding all of the #include's and #define's as well? There are programs floating around called unifd... 2016-01-29, 1732👍, 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, 1732👍, 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, 1731👍, 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, 1730👍, 0💬

I am having trouble with a Turbo C program which crashes
I'm having trouble with a Turbo C program which crashes and says something like ``floating point formats not linked.'' Some compilers for small machines, including Turbo C (and Ritchie's original PDP-11 compiler), leave out certain floating point support if it looks like it will not be needed. In pa... 2015-06-19, 1729👍, 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, 1728👍, 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, 1724👍, 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