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How do I send escape sequences to control a terminal or other device?
How do I send escape sequences to control a terminal or other device? If you can figure out how to send characters to the device at all , it's easy enough to send escape sequences. In ASCII, the ESC code is 033 (27 decimal), so code like fprintf(ofd, "\033[J"); sends the sequence ESC [ J . Some prog... 2015-04-20, 1643👍, 0💬

Can I declare main as void, to shut off these annoying ....
Can I declare main as void, to shut off these annoying ``main returns no value'' messages? No. main must be declared as returning an int, and as taking either zero or two arguments, of the appropriate types. If you're calling exit() but still getting warnings, you may have to insert a redundant retu... 2015-12-20, 1642👍, 0💬

What printf format should I use for a typedef like size_t when I don't know whether it is long or some other type?
What printf format should I use for a typedef like size_t when I don't know whether it is long or some other type? Use a cast to convert the value to a known, conservatively-sized type, then use the printf format matching that type. For example, to print the size of a type, you might use printf("%lu... 2015-11-04, 1642👍, 0💬

How can I open files mentioned on the command line, and parse option flags?
How can I open files mentioned on the command line, and parse option flags? Here is a skeleton which implements a traditional Unix-style argv parse, handling option flags beginning with -, and optional filenames. (The two flags accepted by this example are -a and -b; -b takes an argument.) #include ... 2015-03-11, 1642👍, 0💬

Why doesnt long int work?
Why doesn't long int n = 123456; printf("%d\n", n); work? Whenever you print long ints you must use the l (lower case letter ``ell'') modifier in the printf format (e.g. %ld). printf can't know the types of the arguments which you've passed to it, so you must let it know by using the correct format ... 2015-11-09, 1640👍, 0💬

What is C language?
What is C language? The C programming language is a standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX operating system. It has since spread to many other operating systems, and is one of the most widely used programming languages. C... 2014-12-31, 1639👍, 0💬

What is the difference between memcpy and memmove?
What is the difference between memcpy and memmove? memmove offers guaranteed behavior if the memory regions pointed to by the source and destination arguments overlap. memcpy makes no such guarantee, and may therefore be more efficiently implementable. When in doubt, it's safer to use memmove. It se... 2015-12-07, 1637👍, 0💬

I am trying to sort an array of strings with qsort, using strcmp as the comparison function, but it is not working.
I am trying to sort an array of strings with qsort, using strcmp as the comparison function, but it is not working. By ``array of strings'' you probably mean ``array of pointers to char.'' The arguments to qsort's comparison function are pointers to the objects being sorted, in this case, pointers t... 2015-08-12, 1636👍, 0💬

Is exit status truly equivalent to returning the same status from main?
Is exit status truly equivalent to returning the same status from main? Yes and no. The Standard says that a return from the initial call to main is equivalent to calling exit. However, a return from main cannot be expected to work if data local to main might be needed during cleanup;A few very old,... 2015-12-16, 1635👍, 0💬

I am trying to do some simple trig...
I'm trying to do some simple trig, and I am #including &lt;math.h>, but the linker keeps complaining that functions like sin and cos are undefined. Make sure you're actually linking with the math library. For instance, due to a longstanding bug in Unix and Linux systems, you usually need to use ... 2015-07-01, 1635👍, 0💬

I am sure I've got the trig functions declared correctly, but they are still giving me wrong answers.
I am sure I've got the trig functions declared correctly, but they are still giving me wrong answers. You weren't handing them angles in degrees, were you? C's trig functions (like FORTRAN's and most other languages) accept angles in radians. The conversion from degrees to radians is simple enough: ... 2015-06-29, 1635👍, 0💬

How can I determine whether a machines byte order is big-endian or little-endian?
How can I determine whether a machines byte order is big-endian or little-endian? The usual techniques are to use a pointer: int x = 1; if(*(char *)&amp;x == 1) printf("little-endian\n"); else printf("big-endian\n"); or a union: union { int i; char c[sizeof(int)]; } x; x.i = 1; if(x.c[0] == 1) p... 2015-02-16, 1633👍, 0💬

Can I use an ifdef in a #define line ...
Can I use an #ifdef in a #define line, to define something two different ways, like this? #define a b \ #ifdef whatever c d #else e f g #endif No. You can't ``run the preprocessor on itself,'' so to speak. What you can do is use one of two completely separate #define lines, depending on the #ifdef s... 2016-02-03, 1631👍, 0💬

How can I include expansions of the macros .....
How can I include expansions of the __FILE__ and __LINE__ macros in a general-purpose debugging macro? One solution involves writing your debug macro in terms of a varargs function , and an auxiliary function which stashes the values of __FILE__ and __LINE__ away in static variables, as in: #include... 2016-01-15, 1631👍, 0💬

How can I tell how much destination buffer space ...
How can I tell how much destination buffer space I'll need for an arbitrary sprintf call? How can I avoid overflowing the destination buffer with sprintf? When the format string being used with sprintf is known and relatively simple, you can sometimes predict a buffer size in an ad-hoc way. If the f... 2015-10-19, 1630👍, 0💬

What does it really mean for a program to be legal or `valid or ``conforming?
What does it really mean for a program to be legal or `valid or ``conforming? Simply stated, the Standard talks about three kinds of conformance: conforming programs, strictly conforming programs, and conforming implementations. A conforming program is one that is accepted by a conforming implementa... 2015-11-23, 1629👍, 0💬

Is it legal to pass a null pointer as the first argument to realloc? Why would you want to?
Is it legal to pass a null pointer as the first argument to realloc? Why would you want to? ANSI C sanctions this usage (and the related realloc(..., 0), which frees), although several earlier implementations do not support it, so it may not be fully portable. Passing an initially-null pointer to re... 2016-03-16, 1618👍, 0💬

So can I query the malloc package to find out how big an allocated block is?
So can I query the malloc package to find out how big an allocated block is? Unfortunately, there is no standard or portable way. (Some compilers provide nonstandard extensions.) If you need to know, you'll have to keep track of it yourself. 2016-03-24, 1615👍, 0💬

How can I direct output to the printer?
How can I direct output to the printer? Under Unix, either use popen to write to the lp or lpr program, or perhaps open a special file like /dev/lp. Under MS-DOS, write to the (nonstandard) predefined stdio stream stdprn, or open the special files PRN or LPT1. Under some circumstances, another (and ... 2015-04-22, 1613👍, 0💬

But what about main's third argument, envp?
But what about main's third argument, envp? It's a non-standard (though common) extension. If you really need to access the environment in ways beyond what the standard getenv function provides, though, the global variable environ is probably a better avenue (though it's equally non-standard). 2015-12-20, 1608👍, 0💬

I mm compiling a program, and I seem to be missing one of the header files it requires
I mm compiling a program, and I seem to be missing one of the header files it requires There are several situations, depending on what sort of header file it is that's ``missing''. If the missing header file is truly a standard one (that is, one defined by the ANSI C Standard, such as &lt;stdio.... 2016-02-05, 1607👍, 0💬

What is the ANSI C Standard?
What is the ANSI C Standard? In 1983, the American National Standards Institute (ANSI) commissioned a committee, X3J11, to standardize the C language. After a long, arduous process, including several widespread public reviews, the committee's work was finally ratified as ANS X3.159-1989 on December ... 2016-01-15, 1603👍, 0💬

Are pointers really faster than arrays?
Are pointers really faster than arrays? How much do function calls slow things down? Is ++i faster than i = i + 1? Precise answers to these and many similar questions depend of course on the processor and compiler in use. If you simply must know, you'll have to time test programs carefully. (Often t... 2015-02-09, 1599👍, 0💬

I had a frustrating problem which turned out to be caused by the line ....
I had a frustrating problem which turned out to be caused by the line printf("%d", n); where n was actually a long int. I thought that ANSI function prototypes were supposed to guard against argument type mismatches like this. A:When a function accepts a variable number of arguments, its prototype d... 2016-01-11, 1598👍, 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