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People always say that good style is important
People always say that good style is important, but when they go out of their way to use clear techniques and make their programs readable, they seem to end up with less efficient programs. Since efficiency is so important, isn't it necessary to sacrifice some style and readability? It's true that g... 2015-05-06, 1449👍, 0💬

How can I find out if there are characters available for reading?
How can I find out if there are characters available for reading (and if so, how many)? Alternatively, how can I do a read that will not block if there are no characters available? These, too, are entirely operating-system-specific. Some versions of curses have a nodelay function. Depending on your ... 2015-04-29, 1446👍, 0💬

What is the difference between text and binary I/O?
What is the difference between text and binary I/O? In text mode, a file is assumed to consist of lines of printable characters (perhaps including tabs). The routines in the stdio library (getc, putc, and all the rest) translate between the underlying system's end-of-line representation and the sing... 2015-09-21, 1444👍, 0💬

How should functions be apportioned among source files?
How should functions be apportioned among source files? Usually, related functions are put together in one file. Sometimes (as when developing libraries) it is appropriate to have exactly one source file (and, consequently, one object module) per independent function. Other times, and especially for... 2015-05-18, 1436👍, 0💬

How can I implement a delay, or time a users response, with sub-second resolution?
How can I implement a delay, or time a users response, with sub-second resolution? Unfortunately, there is no portable way. Routines you might look for on your system include clock, delay, ftime, gettimeofday, msleep, nap, napms, nanosleep, setitimer, sleep, Sleep, times, and usleep. (A function cal... 2015-03-06, 1435👍, 0💬

My compiler isnt letting me declare a function
My compiler isnt letting me declare a function A; My compiler isn't letting me declare a function int f(...) { } i.e. accepting a variable number of arguments, but with no fixed arguments at all. A: Standard C requires at least one fixed argument, in part so that you can hand it to va_start. (In any... 2015-06-08, 1433👍, 0💬

What is the deal on sprintfs return value?
What's the deal on sprintf's return value? Is it an int or a char *? The Standard says that it returns an int (the number of characters written, just like printf and fprintf). Once upon a time, in some C libraries, sprintf returned the char * value of its first argument, pointing to the completed re... 2015-10-16, 1432👍, 0💬

How can I open files with names like ...
How can I open files with names like ``file1'', ``file2'', ``file3'', etc., where the numeric part is controlled by a variable? Basically I want ``file%d'', like printf.. You want printf's close cousin sprintf, which ``prints'' to a string: char filename[FILENAME_MAX]; sprintf(filename, "file%d", i)... 2015-10-07, 1432👍, 0💬

How can I change their mode to binary?
I'm writing a ``filter'' for binary files, but stdin and stdout are preopened as text streams. How can I change their mode to binary? There is no standard way to do this. On Unix-like systems, there is no text/binary distinction, so there is no need to change the mode. Some MS-DOS compilers supply a... 2015-09-21, 1432👍, 0💬

How can I insert or delete a line (or record) in the middle of a file?
How can I insert or delete a line (or record) in the middle of a file? In general, there is no way to do this. The usual solution is simply to rewrite the file. When you find yourself needing to insert data into an existing file, here are a few alternatives you can try: * Rearrange the data file so ... 2015-04-13, 1432👍, 0💬

What is the most efficient way to count the number of bits which are set in an integer?
What is the most efficient way to count the number of bits which are set in an integer? Many ``bit-fiddling'' problems like this one can be sped up and streamlined using lookup tables (but see question 20.13). Here is a little function which computes the number of bits in a value, 4 bits at a time: ... 2015-02-11, 1431👍, 0💬

I need a random true/false value ...
I need a random true/false value, so I'm just taking rand() % 2, but it's alternating 0, 1, 0, 1, 0... Poor pseudorandom number generators (such as the ones unfortunately supplied with some systems) are not very random in the low-order bits. (In fact, for a pure linear congruential random number gen... 2015-07-24, 1428👍, 0💬

How do I convert a string to all upper or lower case?
How do I convert a string to all upper or lower case? Some libraries have routines strupr and strlwr or strupper and strlower, but these are not Standard or portable. It's a straightforward exercise to write upper/lower-case functions in terms of the toupper and tolower macros in &lt;ctype.h>;(T... 2015-08-19, 1423👍, 0💬

My floating-point calculations are acting strangely and giving me different answers on different machines.
My floating-point calculations are acting strangely and giving me different answers on different machines. If the problem isn't that simple, recall that digital computers usually use floating-point formats which provide a close but by no means exact simulation of real number arithmetic. Among other ... 2015-06-29, 1422👍, 0💬

How can I write a function analogous to scanf
How can I write a function analogous to scanf, i.e. that accepts similar arguments, and calls scanf to do most of the work? C99 (but not any earlier C Standard) supports vscanf, vfscanf, and vsscanf. 2015-06-12, 1415👍, 0💬

I cant even get a simple fopen call to work
I can't even get a simple fopen call to work! What's wrong with this call? FILE *fp = fopen(filename, 'r'); fopen's mode argument must be a string, like "r", not a character like 'r'. 2015-10-09, 1411👍, 0💬

How can I arrange to have output go two places at once, e.g. to the screen and to a file?
How can I arrange to have output go two places at once, e.g. to the screen and to a file? You can't do this directly, but you could write your own printf variant which printed everything twice. Here is a sample logprintf function which prints to both stdout and a preopened log file: #include &lt... 2015-09-29, 1406👍, 0💬

I know that the library function localtime will convert ...
I know that the library function localtime will convert a time_t into a broken-down struct tm, and that ctime will convert a time_t to a printable string. How can I perform the inverse operations of converting a struct tm or a string into a time_t? ANSI C specifies a library function, mktime, which ... 2015-08-05, 1406👍, 0💬

How can I sort more data than will fit in memory?
How can I sort more data than will fit in memory? You want an ``external sort,'' which you can read about in Knuth, Volume 3. The basic idea is to sort the data in chunks (as much as will fit in memory at one time), write each sorted chunk to a temporary file, and then merge the files. Your operatin... 2015-08-07, 1402👍, 0💬

How can I get back to the interactive keyboard if stdin is redirected?
I'm trying to write a program like ``more.'' How can I get back to the interactive keyboard if stdin is redirected? There is no portable way of doing this. Under Unix, you can open the special file /dev/tty. Under MS-DOS, you can try opening the ``file'' CON, or use routines or BIOS calls such as ge... 2015-09-29, 1397👍, 0💬

How can I recover the file name given an open stream?
How can I recover the file name given an open stream? This problem is, in general, insoluble. Under Unix, for instance, a scan of the entire disk (perhaps involving special permissions) would theoretically be required, and would fail if the descriptor were connected to a pipe or referred to a delete... 2015-10-05, 1392👍, 0💬

I am getting strange syntax errors on the very first declaration in a file, but it looks fine.
I am getting strange syntax errors on the very first declaration in a file, but it looks fine. Perhaps there's a missing semicolon at the end of the last declaration in the last header file you're #including. 2016-02-12, 1391👍, 0💬

I need code to parse and evaluate expressions.
I need code to parse and evaluate expressions. Two available packages are ``defunc,'' posted to comp.sources.misc in December, 1993 (V41 i32,33), to alt.sources in January, 1994, and available from sunsite.unc.edu in pub/packages/development/libra ries/defunc-1.3.tar.Z,and ``parse,'' at lamont.ldgo.... 2015-05-01, 1390👍, 0💬

How can I delete a file?
How can I delete a file? The Standard C Library function is remove. (This is therefore one of the few questions in this section for which the answer is not ``It's system-dependent.'') On older, pre-ANSI Unix systems, remove may not exist, in which case you can try unlink. 2015-04-10, 1367👍, 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