void | 易学教程

【转载】在JavaScript中使用操作符void返回undefined

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在JavaScript中使用操作符void返回undefined 技术 maybe yes 发表于 2014-12-30 18:45 原文链接 : http://blog.lmlphp.com/archives/53 来自 : LMLPHP后院在 JavaScript 函数中返回 undefined 的同时执行一个表达式，可以使用 void 关键字。大家比较熟悉的 void 的用法一般都是在链接的 href 属性中，可以屏蔽<a>标签的默认行为。请看下面的代码片段： <script> function(t){ return o?t():void i.push(t) } </script> 在 JavaScript 中使用 void 操作任何一个表达式的返回值都是 undefined。在函数中获得 undefined 也有其他的方式，请看下面的例子，代码片段摘自LMLJS框架： <script> (function(win, doc, undf){ })(window, document); </script> 上面的匿名函数中，在定义参数时多定义了一个，没有传入的参数默认值就是 undefined 。关于在 JavaScript 中如何获取 undefined ？直接使用 undefined 其实是不严谨的，因为 "undefined" 在 JavaScript 中并不是保留字

G++ error: ‘<anonymous>’ has incomplete type

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问题 I am forced to use a third party dongle access library that provides an include file 'sense4.h' with code as follows: #if !defined _WINDOWS_ #define WINAPI #define CONST const typedef unsigned char UCHAR; typedef unsigned short USHORT; typedef unsigned int UINT; typedef unsigned long ULONG; typedef char CHAR; typedef char TCHAR; typedef void VOID; ... #endif /* !defined _WINDOWS */ ... unsigned long WINAPI S4Startup( VOID ); unsigned long WINAPI S4Cleanup( VOID ); ... The problem is that g++

Two function declarations with void and empty argument list

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问题 I'd like to know why the following code: void foo(void); void foo() { } is valid in gcc. In C, there is no such thing as overloading and above declarations (in fact, one of them is a definition) declare two different functions (the first one doesn't take any arguments, the second one could take any number of arguments of any types). However, if we provide a definition for the first function: void foo(void) { } void foo() { } a compilation fails this time due to redefinition. But still , the

void* is literally float, how to cast?

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问题 So I'm using this C library in my C++ app, and one of the functions returns a void*. Now I'm not the sharpest with pure C, but have heard that a void* can be cast to pretty much any other *-type. I also know that I expect a float at the end somewhere from this function. So I cast the void* to a float* and dereference the float*, crash. darn!. I debug the code and in gdb let it evaluate (float)voidPtr and low and behold the value is what I expect and need! But wait, it's impossible to the same

When can “void()” be used and what are the advantages of doing so

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问题 I started learning the C language recently, and have noted the function "void()", however, I would like to know what it does and it's best points of application, also perhaps an alternative to void that is potentially more productive. Thank you. 回答1: There is no function called void , but a function can be declared with a return type of void . This means that the function doesn't return a value. void DoSomething(...) { .... } Update void can also be used to indicate to the compiler that the

How to return data from void function?

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So, around a week ago I asked a question about activex and UDP. Here it is: C# UDP Socket client and server Now, I created two applications, one (the sender) to send pre-defined strings via UDP. The other is activex component that is called from a webpage, and it's thread is working in the background. Once an UDP message arrives, then it's doing it's stuff (writing in database, writing in log.txt, and so on). The last thing i need is to return data (it's yet to be said if it will be string or something else). However, the method in the activex which is called must be a void, because if it's

Use instanceof Void in java

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I want to use the type of void java but I can't. Here is a my code which is an aspect run after to all methods which have @TraceLog annotations @AfterReturning(value = "@annotation(log)", returning = "returnValue", argNames = "joinPoint, log, returnValue" ) public void afterReturning(final JoinPoint joinPoint, final TraceLog log, final Object returnValue) { Class<?> returnType = ((MethodSignature) joinPoint.getSignature()) .getReturnType(); //It works when comperaing with string. But I want to write it with type of if ("void".equals(returnType.getName()) ) { //Do some log } } As a coding rule

Can't compile with void variable in C

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问题 test.c int main () { void a; return 0; } I use gcc to compile but it gives me an error: error: variable or field 'a' declared void From what I read here, I thought I can declare void variable without problem. 回答1: As your link states: A variable that is itself declared void (such as my_variable above) is useless; it cannot be assigned a value, cannot be cast to another type, in fact, cannot be used in any way. This means that although syntactically correct, a void declaration is not useful to

From Java Object class to C++

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I'm relative new to C++ and my background is in Java. I have to port some code from Java to C++ and some doubts came up relative to the Object Java's class. So, if I want to port this: void setInputParameter(String name, Object object) { ..... } I believe I should use void* type or templates right? I don't know what's the "standard" procedure to accomplish it. Thanks It depends what you want to do with object . If you use a template, then any methods you call on object will be bound at compile time to object s type. This is type safe, and preferable, as any invalid use of the object will be

Void vs Int Functions

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What would be the different between void and int functions? When do i use which? Would void be used when just printing out a message or a variable value? like cout << value; Or would it just be text? And is int used when you actually do calculations within it? void is used when you are not required to return anything from the function to the caller of the function. for eg. void no_return_fn() { cout<< "This function will not return anything" << endl; return; // returns nothing or void } int is used when you have to return an integer value from the function to the caller of the function for eg.