void

问题 Is void a data type in the C programming language? If so, what type of values can it store? If we have int , float , char , etc., to store values, why is void needed? And what is the range of void? 回答1: Void is considered a data type (for organizational purposes), but it is basically a keyword to use as a placeholder where you would put a data type, to represent "no data". Hence, you can declare a routine which does not return a value as: void MyRoutine(); But, you cannot declare a variable

问题 I'm looking at a path finding tutorial and I noticed a return statement inside a void method (class PathTest , line 126): if ((x < 0) || (y < 0) || (x >= map.getWidthInTiles()) || (y >= map.getHeightInTiles())) { return; } I'm a novice at Java. Can anyone tell me why it's there? As far as I knew, return inside a void method isn't allowed. 回答1: It just exits the method at that point. Once return is executed, the rest of the code won't be executed. eg. public void test(int n) { if (n == 1) {

问题 What does it mean to convert an integer value to a void* or viceversa from a memory point of view? My understanding is void* is an address to a block of memory of unspecified length. This seems to be something like comparing apple with oranges. int myval = 5; void* ptr = (void*)myval; printf("%d",(int)ptr); I realized that I should have given the exact context where this is used. int main(int argc, char* argv[]) { long thread; /* Use long in case of a 64-bit system */ pthread_t* thread

问题 An often used statement like (void)x; allows to suppress warnings about unused variable x . But if I try compiling the following, I get some results I don't quite understand: int main() { int x; (short)x; (void)x; (int)x; } Compiling this with g++, I get the following warnings: $ g++ test.cpp -Wall -Wextra -o test test.cpp: In function ‘int main()’: test.cpp:4:13: warning: statement has no effect [-Wunused-value] (short)x; ^ test.cpp:6:11: warning: statement has no effect [-Wunused-value]

问题 I've seen some people using void operator in their code. I have also seen this in href attributes: javascript:void(0) which doesn't seem any better than javascript:; So, what is the justification of using the void operator? 回答1: The JavaScript, the void operator is used to explicitly return undefined. Its a unary operator, meaning only one operand can be used with it. You can use it like shown below — standalone or with a parenthesis. void expression; void(expression); Lets see some examples

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 9 months ago . Let's say you have a method or a cmdlet that returns something, but you don't want to use it and you don't want to output it. I found these two ways: Add-Item > $null [void]Add-Item Add-Item | Out-Null What do you use? Which is the better/cleaner approach? Why? 回答1: I just

问题 So, I found a similar question here, but the answers are more about style and whether or not you are able to do it. My question is, what actually happens when you call a non-void function that returns an object, but you never assign or use said returned object? So, less about whether or not you can, because I absolutely know you can and understand the other question linked above... what does the compiler/runtime environment do? This is not a language specific question, but if you answer,

问题 I have got this error on the line where the void is it says undeclared identifier for sliderDidChange can some one please help me with this i can;t find any answers. h. file // // LightViewController.h // Flash Light // // Created by John Whitney on 12-07-27. // Copyright (c) 2012 Perfect Programs. All rights reserved. // #import <UIKit/UIKit.h> #import <AVFoundation/AVFoundation.h> @interface LightViewController : UIViewController { IBOutlet UISlider *slider; IBOutlet UISlider *theslider;

问题 I have a theoretical question: but every method and IbAction must be declared in .h??? Because if I write a method (void) in .m and not in .h the project not has problem. 回答1: If you wanna access a function from another class you're gonna import that .h header file to make your compiler understand where to find those functions and how to translate them. 回答2: It is a guideline for how to implement your classes. Think of it in "C" terms. You define your prototypes in the .h (header) file and do

问题 In my answer I mention that dereferencing a void pointer is a bad idea. However, what happens when I do this? #include <stdlib.h> int main (void) { void* c = malloc(4); *c; &c[0]; } Compilation: gcc prog.c -Wall -Wextra prog.c: In function 'main': prog.c:4:2: warning: dereferencing 'void *' pointer *c; ^~ prog.c:5:4: warning: dereferencing 'void *' pointer &c[0]; ^ prog.c:5:2: warning: statement with no effect [-Wunused-value] &c[0]; ^ Here is an image from Wandbox for those who say it didn't