undefined | 易学教程

static ints, compilation units and the ternary operator

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问题 // SomeCls.h class SomeCls { static const int PERIOD_ALARM_NORMAL = 5; static const int PERIOD_ALARM_THRESH = 1; void method() { bool b = true; const int d = b ? PERIOD_ALARM_THRESH : PERIOD_ALARM_NORMAL; } } obj; It is going to build ok. Now take out the method() implementation and place it in a cpp file: //SomeCls.cpp #include "SomeCls.h" void SomeCls::method() { bool b = true; const int d = b ? PERIOD_ALARM_THRESH : PERIOD_ALARM_NORMAL; } Why does mr. linker say undefined reference to

Nuxtjs with scrollmagic gives me “window is not defined”

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问题 I want to use scrollmagic with nuxtjs. I installed scrollmagic via npm. npm install scrollmagic In my nuxt.config.js file i added build: { vendor: ['scrollmagic'] }, And in my pages/index.vue file i simply imported it. import ScrollMagic from 'scrollmagic' But this results only in this error [vue-router] Failed to resolve async component default: ReferenceError: window is not defined [vue-router] uncaught error during route navigation: ReferenceError: window is not defined at C:\pathto\node

Is there a functional equivalent to mysqli_fetch_all in PHP 5.2?

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问题 So, I am a total n00b at PHP (and back-end programming in general), but I never the less decided I wanted to build a functioning database that users could search client-side as th final project for my first web dev class. Anyway, I made my site and database on a localhost, and though it took a while, I got everything functioning perfectly. When I tried to move it to my webhost, however, everything started breaking because, previously unbeknownst to me, the webhost is using PHP 5.2. I've been

Why does DrJava return a Static Error?

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问题 I use dr java for linux to run my code. I've been running into a bunch of errors recently while running this simple program. The code compiles fine but whenever I run the java file, I get the error; Static Error: Undefined name here's my code; (I've got two files, Square.java and SquareD.java) Here's Square.java public class Square{ private String name; private int y; private int x; public Square(String st,int x2,int y2){ name=st; x=x2; y=y2; } public int square(){ return x*x+y*y; } double a1

JSON object properties are undefined

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问题 I'm getting a JSON object back from an AJAX call and logging the result like this: console.log(response); And this is the response logged in the console: {"filename":"new.jpg","orientation":"vertical"} However, when I console.log(response.orientation); I get a response that it is undefined. Most of the answers I've read indicate that an array was returned instead of an object and that response[0].orientation should work, but that is not the case here. When I assign the same array to another

Error building OpenCV 2.4.x “Undefined reference to av_opt_set@LIBAVUTIL_51”

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问题 I have tried building all versions of 2.4, and they all fail when "Linking CXX executable ../../bin/opencv_test_core" with: /usr/local/lib/libavcodec.so.54: undefined reference to `av_opt_set@LIBAVUTIL_51' /usr/local/lib/libavformat.so.54: undefined reference to `av_strcasecmp@LIBAVUTIL_51' /usr/local/lib/libavcodec.so.54: undefined reference to `av_bprint_finalize@LIBAVUTIL_51' /usr/local/lib/libavformat.so.54: undefined reference to `av_timecode_make_smpte_tc_string@LIBAVUTIL_51' /usr/local

Undefined method `+@' for false:FalseClass (NoMethodError) ruby

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问题 def next_prime_number (last_known_prime) while true last_known_prime++ found_factor = false # ERROR for i in 1...last_known_prime if last_known_prime % i == 0 found_factor = true break end end if !found_factor puts "new prime: #{last_known_prime}" Kernel.exit end end end in `next_prime_number': undefined method `+@' for false:FalseClass (NoMethodError) I'm getting the above error and am totally stumped. Any ideas (no, this is not homework, I am trying to teach myself Ruby through the Euler

Highcharts: Cannot read property 'parts/Globals.js' of undefined

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问题 I am using certain libraries from Highcharts and I get the following error: Uncaught TypeError: Cannot read property 'parts/Globals.js' of undefined at map.src.js:31 at map.src.js:22 at map.src.js:11 How can I fix this? I am using: <script src="https://code.highcharts.com/maps/modules/map.js"></script> 回答1: Faced the same issue. Highcharts released a new version 7.1.0 two days back. They have fixed an issue(10232) which is causing this error. You can use https://code.highcharts.com/5.0.14

Undefined variable $loop in Laravel Blade loop

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问题 according to the latest laravel blade documentation (https://laravel.com/docs/5.3/blade see "loops") I can "[...] use the loop variable to gain valuable information about the loop[...]". My laravel version is up to date but inside my foreach loop I can't access the $loop variable. It says "undefined variable $loop". Example: @foreach( $values["rating"] as $rating ) @if( $loop->iteration == 3 ) -- do something -- @endif @endforeach Does anyone know a solution for this? Thank you so much! 回答1:

js null,undefined判断

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var exp = null ; if (! exp ) 如果 exp 为 undefined，或数字零，或 false，也会得到与 null 相同的结果，虽然 null 和二者不一样。注意：要同时判断 null、undefined、数字零、false 时可使用本法。 var exp = null ; if (! exp && typeof exp != "undefined" && exp != 0) { alert ( "is null" ); } typeof exp != "undefined" 排除了 undefined； exp != 0 排除了数字零和 false。更简单的正确的方法： var exp = null ; if ( exp === null ) { alert ( "is null" ); } 尽管如此，我们在 DOM 应用中，一般只需要用 (!exp) 来判断就可以了，因为 DOM 应用中，可能返回 null，可能返回 undefined，如果具体判断 null 还是 undefined 会使程序过于复杂。来源： https://www.cnblogs.com/henw/archive/2011/05/12/2044166.html