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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, 1714👍, 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, 1710👍, 0💬

What is a good data structure to use for storing lines of text?
What's a good data structure to use for storing lines of text? I started to use fixed-size arrays of arrays of char, but they're just too restrictive. One good way of doing this is with a pointer (simulating an array) to a set of pointers (each simulating an array) of char. This data structure is so... 2015-02-25, 1708👍, 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, 1702👍, 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, 1702👍, 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, 1698👍, 0💬

Is there a way to have non-constant case labels (i.e. ranges or arbitrary expressions)?
Is there a way to have non-constant case labels (i.e. ranges or arbitrary expressions)? No. The switch statement was originally designed to be quite simple for the compiler to translate, therefore case labels are limited to single, constant, integral expressions. You can attach several case labels t... 2015-02-02, 1697👍, 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, 1696👍, 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, 1695👍, 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, 1695👍, 0💬

Why doesn't sizeof tell me the size of the block of memory pointed to by a pointer?
Why doesn't sizeof tell me the size of the block of memory pointed to by a pointer? sizeof tells you the size of the pointer. There is no portable way to find out the size of a malloc'ed block. (Remember, too, that sizeof operates at compile time 2016-03-21, 1694👍, 0💬

Does C have an equivalent to Pascals with statement?
Does C have an equivalent to Pascals with statement? No. The way in C to get quick and easy access to the fields of a structure is to declare a little local structure pointer variable (which, it must be admitted, is not quite as notationally convenient as a with statement and doesn't save quite as m... 2015-01-14, 1694👍, 0💬

I am starting to think about multinational character sets ....
I'm starting to think about multinational character sets, and I'm worried about the implications of making sizeof(char) be 2 so that 16-bit character sets can be represented. If type char were made 16 bits, sizeof(char) would still be 1, and CHAR_BIT in &lt;limits.h> would be 16, and it would si... 2016-03-02, 1691👍, 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, 1691👍, 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, 1691👍, 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, 1690👍, 0💬

How can I list all of the predefined identifiers?
How can I list all of the predefined identifiers? There's no standard way, although it is a common need. gcc provides a -dM option which works with -E, and other compilers may provide something similar. If the compiler documentation is unhelpful, the most expedient way is probably to extract printab... 2016-01-27, 1689👍, 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, 1688👍, 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, 1688👍, 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, 1686👍, 0💬

Why does the call char scanf work?
Why does the call char s[30]; scanf("%s", s); work? I thought you always needed an & on each variable passed to scanf. You always need a pointer; you don't necessarily need an explicit &amp;. When you pass an array to scanf, you do not need the &, because arrays are always passed to func... 2015-10-30, 1685👍, 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, 1684👍, 0💬

Why is my simple program, which hardly does more than print
Why is my simple program, which hardly does more than print ``Hello, world!'' in a window, compiling to such a huge executable (several hundred K)? Should I #include fewer header files? What you're seeing is the current (poor) state of the ``art'' in library design. As run-time libraries accrete mor... 2015-07-06, 1684👍, 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, 1682👍, 0💬

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