undefined | 易学教程

A question about union in C - store as one type and read as another - is it implementation defined?

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问题 I was reading about union in C from K&R, as far as I understood, a single variable in union can hold any one of the several types and if something is stored as one type and extracted as another the result is purely implementation defined. Now please check this code snippet: #include<stdio.h> int main(void) { union a { int i; char ch[2]; }; union a u; u.ch[0] = 3; u.ch[1] = 2; printf("%d %d %d\n", u.ch[0], u.ch[1], u.i); return 0; } Output: 3 2 515 Here I am assigning values in the u.ch but

How to add “undefined” to a JObject collection - where is JToken/JValue.Undefined?

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问题 When using Json.NET, I am trying to create a JSON structure dynamically using the "JSON to LINQ" support. In the following, jObject is a JObject and JObject.Add takes (string, JToken). However, I cannot find out how to add either an Undefined or a Null token - nor can I find out how to create JValues with the appropriate Null/Undefined type. string value = GetValue(); if (value == "undefined") { jObject.Add(key, /* how to add "Undefined" token? */); } else if (value == "null") { jObject.Add

JS Cannot read property “length” of undefined [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 2 years ago . I'm trying to create an object using a given string where each word has a property stating its length. var strings = {}; function findLongestWord(str) { var splitStr = str.split(" "); for (var i = 0; i <= str.length; i++){ strings[splitStr[i]] = splitStr[i].length; } return strings; } findLongestWord("The quick

Undefined variable, which is actually defined

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问题 I have my $dbConnection variable set at the very top of the page. And I have a contact form included on the same page. The contact form works fine. However, when submitting, it gives me an undefined error; that's weird because I'm 199% sure I have the variable set correctly. The form is going through a script. function ubbreplace($text){ if (strpos($text, "[contact-form]") !== false) { ob_start(); include("contactform.php"); $replace = ob_get_contents(); ob_end_clean(); $text = str_replace("

jQuery uncaught reference error - element is not defined

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问题 I implemented the following plugin in into a drupal website https://github.com/linnett/backgroundVideo following their instructions to the T. I am receiving a jQuery uncaught reference error: element is not defined error. This is my site. 回答1: the variable element is supposed to be a reference to your video element. var element = "#TheVideoElementId"; 回答2: According to the github project and also to the examples which are provided, element is just a placeholder for your <video> wrapper. So if

Rails.env undefined in Rails 2

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问题 I have an older application running Ruby on Rails 2.2, and I'm having trouble getting a gem to work because it can't find the current environment with Rails.env : $ script/console >> Rails.env NoMethodError: undefined method `env' for Rails:Module from (irb):1 The gem is set up to use Rails.env when Rails is defined, and RAILS_ENV when it's not. But I seem to have a Rails object without an env method (even though I read that method was added in Rails 2). Any idea what's going on? 回答1: The

判定类型

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目前最精确的判定方法（不包括自定义类型） //2010.6.1更新 var is = function (obj,type) { return (type === "Null" && obj === null) || (type === "Undefined" && obj === void 0 ) || (type === "Number" && isFinite(obj)) || Object.prototype.toString.call(obj).slice(8,-1) === type; }, 用法如下： //***************示例一，判定数组与函数 var forEach = function(array,fn,bind){ if(is(array,"Array") && is(Array.forEach,"Function")){ array.forEach(fn,bind); }else{ for(var i=0,n=array.length;i<n;i++){ i in array && fn.call(bind,array[i],i,array) } } } //***************示例二，判定null var a = null alert(is(a,"Null")) //***************示例二，判定undefined var

Why is my function returning undefined?

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问题 The function validate() is returning undefined, when I expected it to return false or true. Why is this happening? Now I'm just typing this because stackoverflow won't let me post this question, since it is mostly code. function validate() { var isFormValid = false; var emailValid = false; var inputValid = false; var passValid = true; //VALIDATE EMAIL var emailInput = $("input[type='email']"); $.get("/checkEmail", { email: emailInput.val() }, function(data) { if (data.userExists) { emailInput

Why is my function returning undefined?

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Rails 3: undefined method messages for Folder

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问题 I'm running Rails 3 and like to have a message system. Here is the tutorial for it: http://www.novawave.net/public/rails_messaging_tutorial.html It's for Rails 2 so I was trying to implement it in Rails 3. Everything went fine and i can send messages. But when i like to check my inbox this error shows up: undefined method `messages' for #<Folder:0x0000010419fd48> Mailbox Controller: class MailboxController < ApplicationController def index redirect_to new_session_path and return unless logged