declaration | 易学教程

C function declaration within another function

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问题 can anyone explain these lines to me: int xyz( void ) { extern void abc( void ); } a function declaration within a function definition? or am I missunderstanding something? 回答1: Yes, your guess is correct. It's declaring the existence of the function abc() , so it may be referenced within xyz() . Note that the extern is unnecessary, as functions are extern by default. 回答2: The "extern" declaration in C is to indicate the existence of, and the type of, a global variable or function. An extern

Why does Java allow type-unsafe Array assignments?

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Generally, Java can be considered as a type-safe language. I know that there are some flaws with generics, but I recently came across a Problem I never had before. To break it down: Object[] objects = new Integer[10]; objects[0] = "Hello World"; will NOT result in a compile-time error as expected. I would assume that the declaration of an Array of Object will disallow to point to to an array of something else. In Generics I'm not allowed to make such weird things like: ArrayList<Object> objs = new ArrayList<Integer> and if I try to kind of trick Java into doing something with ArrayList<?

Declarations, definitions, initializations in C, C++, C#, Java and Python [closed]

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问题 It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 7 years ago . What do the terms mean in each of the above languages? Why do the languages differ (wherever they do, if at all they do) in this respect? 回答1: C/C++: A declaration is a statement that says "here is the name of

C++/CLI : Advantages over C#

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问题 Is there any major advantage of managed C++/CLI over C#. Definitely not the syntax I suppose as the following code in C++/CLI is real ugly, C++/CLI code: [Out]List<SomeObject^>^% someVariable Compare above with C# Code: out List<SomeObject> someVariable Just out of curiosity, is there an even uglier syntax in C++/CLI as compared to the above. 回答1: It's almost exclusively an interopability language - both for allowing .Net code to access legacy C++ libraries, or for extended existing (native)

Is it possible to create a type alias to a generic class in Delphi

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问题 I would like to define a class type (type alias) for a generic class. I would like to do this so users of unit b can have access to TMyType without using unit a. I have units like this: unit a; interface type TMyNormalObject = class FData: Integer; end; TMyType<T> = class FData: <T>; end; implementation end. unit b; interface type TMyNormalObject = a.TMyNormalObject; // works TMyType<T> = a.TMyType<T>; // E2508 type parameters not allowed on this type implementation end. I already found a

What are the differences between $, @, % in Perl variable declaration? [duplicate]

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This question already has an answer here: What is the difference between `$this`, `@that`, and `%those` in Perl? 5 answers Example: my $some_variable; my @some_variable; my %some_variable; I know, @ seems to be for array, $ for primitive, is it totally right? What is % for? One of the nice things about Perl is that it comes with a built in manual. Type in the following command: perldoc perlintro and take a look at the section Perl variable types . You can also see this on line with the perldoc.perl.org section on Perl variables. A quick overview: $foo is a scalar variable. It can hold a single

What's the benefit for a C source file include its own header file

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问题 I understand that if a source file need to reference functions from other file then it needs to include its header file, but I don't understand why the source file include its own header file. Content in header file is simply being copied and pasted into the source file as function declarations in per-processing time. For source file who include its own header file, such "declaration" doesn't seem necessary to me, in fact, project still compile and link no problem after remove the header from

Variables scope which are defined within a while block in stored procedures - SQl Server

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I've come across a interesting scenario (at least for me) in a stored procedure. Would like to have experts opinion and thoughts on it. DECLARE @loopcounter INT SET @loopcounter=10 WHILE @loopcounter > 0 BEGIN DECLARE @insidevalue int IF (@loopcounter%2 = 0) SET @insidevalue = @loopcounter PRINT 'Value_' + CAST(@insidevalue AS NVARCHAR) + '_' SET @loopcounter = @loopcounter - 1 END I was expecting this block will give the output as below Value_10_ Value_ _ Value_8_ Value_ _ Value_6_ Value_ _ Value_4_ Value_ _ Value_2_ Value_ _ Instead I got output as below: Value_10_ Value_10_ Value_8_ Value_8

How to create an Array, ArrayList, Stack and Queue in Java?

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I was reading a Java article, but found no differences in the declaration and was confused over. Can anyone list me out this? Added the Article http://www.theparticle.com/javadata2.html Anthony Forloney Without more details as to what the question is exactly asking, I am going to answer the title of the question, Create an Array : String[] myArray = new String[2]; int[] intArray = new int[2]; // or can be declared as follows String[] myArray = {"this", "is", "my", "array"}; int[] intArray = {1,2,3,4}; Create an ArrayList : ArrayList<String> myList = new ArrayList<String>(); myList.add("Hello")

When do I define objective-c methods?

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I'm learning Objective-C, and have a C/C++ background. In object-oriented C++, you always need to declare your method before you define (implement) it, even if it is declared in the parent class. In procedural-style C, IIRC, you can get away with just defining a function so long as it is only called from something else in the same compilational unit (ie. the same file) that came later on in the file (well, provided you don't declare it elsewhere with "extern"). Now, in Objective-C, it appears that you only need to declare selectors in the header file if they are going to be used by something