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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, 1646👍, 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, 1645👍, 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, 1643👍, 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, 1642👍, 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, 1638👍, 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, 1634👍, 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, 1632👍, 0💬

How can I write a macro which takes a variable number of arguments ....
How can I write a macro which takes a variable number of arguments, or use the preprocessor to ``turn off'' a function call with a variable number of arguments? One popular trick is to define and invoke the macro with a single, parenthesized ``argument'' which in the macro expansion becomes the enti... 2016-01-19, 1631👍, 0💬

I am trying to use the ANSI stringizing preprocessing operator ....
I'm trying to use the ANSI ``stringizing'' preprocessing operator `#' to insert the value of a symbolic constant into a message, but it keeps stringizing the macro's name rather than its value. It turns out that the definition of # says that it's supposed to stringize a macro argument immediately, w... 2016-01-22, 1625👍, 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, 1625👍, 0💬

How can I convert integers to binary or hexadecimal?
How can I convert integers to binary or hexadecimal? Make sure you really know what you're asking. Integers are stored internally in binary, although for most purposes it is not incorrect to think of them as being in octal, decimal, or hexadecimal, whichever is convenient. The base in which a number... 2015-02-13, 1625👍, 0💬

What does pragma once mean? I found it in some header files.
What does pragma once mean? I found it in some header files. It is an extension implemented by some preprocessors to help make header files idempotent; that is, to make sure that their contents are processed exactly once even if they are #included multiple times.Some people claim that #pragma once c... 2015-12-11, 1621👍, 0💬

Why are some ANSI ISO Standard library functions showing you
Why are some ANSI/ISO Standard library functions showing up as undefined, even though I've got an ANSI compiler? It's possible to have a compiler available which accepts ANSI syntax, but not to have ANSI-compatible header files or run-time libraries installed. (In fact, this situation is rather comm... 2015-11-30, 1621👍, 0💬

I cant get strcat to work. I tried ...
I can't get strcat to work. I tried char *s1 = "Hello, ";br> char *s2 = "world!";br> char *s3 = strcat(s1, s2);br> but I got strange results. the main problem here is that space for the concatenated result is not properly allocated. C does not provide an automatically-managed string type. C compiler... 2016-03-09, 1620👍, 0💬

How can I do PEEK and POKE in C?
How can I access memory (a memory-mapped device, or graphics memory) located at a certain address? How can I do PEEK and POKE in C? Set a pointer, of the appropriate type, to the right number (using an explicit cast to assure the compiler that you really do intend this nonportable conversion): unsig... 2015-03-20, 1620👍, 0💬

Is there anything like an ifdef for typedefs?
Is there anything like an ifdef for typedefs? Unfortunately, no. (There can't be, because types and typedefs haven't been parsed at preprocessing time.) You may have to keep sets of preprocessor macros (e.g. MY_TYPE_DEFINED) recording whether certain typedefs have been declared. 2016-02-01, 1619👍, 0💬

How can I manipulate individual bits??
How can I manipulate individual bits?? Bit manipulation is straightforward in C, and commonly done. To extract (test) a bit, use the bitwise AND (&amp;) operator, along with a bit mask representing the bit(s) you're interested in: value &amp; 0x04 To set a bit, use the bitwise OR (| or |=) o... 2015-02-20, 1618👍, 0💬

Having dynamically allocated an array , can I change its size?
Having dynamically allocated an array , can I change its size? Yes. This is exactly what realloc is for. Given a region of malloced memory its size can be changed using code like: dynarray = realloc(dynarray, 20 * sizeof(int)); Note that realloc may not always be able to enlarge memory regions in-pl... 2016-03-21, 1617👍, 0💬

What should malloc0 do? Return a null pointer or a pointer to 0 bytes?
What should malloc0 do? Return a null pointer or a pointer to 0 bytes? The ANSI/ISO Standard says that it may do either; the behavior is implementation-defined Portable code must either take care not to call malloc(0), or be prepared for the possibility of a null return. 2015-12-04, 1617👍, 0💬

Why doesnt C have nested functions?
Why doesnt C have nested functions? It's not trivial to implement nested functions such that they have the proper access to local variables in the containing function(s), so they were deliberately left out of C as a simplification. (gcc does allow them, as an extension.) For many potential uses of n... 2015-01-14, 1615👍, 0💬

I can write C code that looks more like Pascal? ....
Here are some cute preprocessor macros: #define begin { #define end } With these, I can write C code that looks more like Pascal. What do y'all think? Use of macros like these, though perhaps superficially attractive, is generally discouraged; in severe cases the practice is called ``preprocessor ab... 2016-02-24, 1613👍, 0💬

Why isnt there a numbered, multi-level break statement to break out
Why isn't there a numbered, multi-level break statement to break out of several loops at once? What am I supposed to use instead, a goto? A:First, remember why it is that break and continue exist at all--they are, in effect, ``structured gotos'' used in preference to goto (and accepted as alternativ... 2015-01-30, 1613👍, 0💬

I am including the right header file for the library function I am using, but the linker keeps saying its undefined.
I am including the right header file for the library function I am using, but the linker keeps saying its undefined. In the general case of calling code in an external library, using #include to pull in the right header file(s) is only half of the story; you also have to tell the linker to search th... 2016-02-10, 1612👍, 0💬

I dont understand why I cant use const values in initializers ....
I don't understand why I can't use const values in initializers and array dimensions, as in const int n = 5; int a[n]; The const qualifier really means ``read-only''; an object so qualified is a run-time object which cannot (normally) be assigned to. The value of a const-qualified object is therefor... 2016-01-08, 1605👍, 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