Web-Dev-For-Beginners | 24 Lessons , 12 Weeks , Get Started as a Web Developer | Learning library

by microsoft JavaScript Version: Current License: MIT

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kandi X-RAY | Web-Dev-For-Beginners Summary

Web-Dev-For-Beginners is a JavaScript library typically used in Institutions, Learning, Education, Tutorial, Learning applications. Web-Dev-For-Beginners has no bugs, it has no vulnerabilities, it has a Permissive License and it has medium support. You can download it from GitHub.

24 Lessons, 12 Weeks, Get Started as a Web Developer

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Web-Dev-For-Beginners has a medium active ecosystem.
It has 44908 star(s) with 6498 fork(s). There are 2318 watchers for this library.
It had no major release in the last 12 months.
There are 4 open issues and 180 have been closed. On average issues are closed in 41 days. There are 6 open pull requests and 0 closed requests.
It has a neutral sentiment in the developer community.
The latest version of Web-Dev-For-Beginners is current.

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Web-Dev-For-Beginners has 0 bugs and 0 code smells.

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Web-Dev-For-Beginners has no vulnerabilities reported, and its dependent libraries have no vulnerabilities reported.
Web-Dev-For-Beginners code analysis shows 0 unresolved vulnerabilities.
There are 0 security hotspots that need review.

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license License

Web-Dev-For-Beginners is licensed under the MIT License. This license is Permissive.
Permissive licenses have the least restrictions, and you can use them in most projects.

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Web-Dev-For-Beginners releases are not available. You will need to build from source code and install.
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It has 970 lines of code, 0 functions and 49 files.
It has low code complexity. Code complexity directly impacts maintainability of the code.

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Top functions reviewed by kandi - BETA

kandi has reviewed Web-Dev-For-Beginners and discovered the below as its top functions. This is intended to give you an instant insight into Web-Dev-For-Beginners implemented functionality, and help decide if they suit your requirements.

create an element position
check for game state changes
Confirms a transaction
Update a game objects .
Initializes game objects .
Update route .
Run game
Updates the account .
Generate the game objects
Main game loop

Web-Dev-For-Beginners Key Features

24 Lessons, 12 Weeks, Get Started as a Web Developer

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Community Discussions

Trending Discussions on Learning

How do purely functional languages handle index-based algorithms?
How can I fix this : Warning: the fonts "Times" and "Times" are not available for the Java logical font "Serif"
Keras AttributeError: 'Sequential' object has no attribute 'predict_classes'
How do I fix CLIENT_MISSING_INTENTS error?
Getting error 'digital envelope routines', reason: 'unsupported', code: 'ERR_OSSL_EVP_UNSUPPORTED'
Vue 3 passing array warning: Extraneous non-props attributes were passed to component but could not be automatically inherited
TypeError: match.loader.options.plugins is not a function
Group and create three new columns by condition [Low, Hit, High]
What should the result be when assigning a variable to a reference to itself, in-between modified and then returned by a function call?
Flutter (2.5) - A splash screen was provided to Flutter, but this is deprecated

Trending Discussions on Learning

QUESTION

How do purely functional languages handle index-based algorithms?

Asked 2022-Apr-05 at 12:51

I have been trying to learn about functional programming, but I still struggle with thinking like a functional programmer. One such hangup is how one would implement index-heavy operations which rely strongly on loops/order-of-execution.

For example, consider the following Java code:

public class Main {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(1,2,3,4,5,6,7,8,9);
        System.out.println("Nums:\t"+ nums);
        System.out.println("Prefix:\t"+prefixList(nums));
    }
  
    private static List<Integer> prefixList(List<Integer> nums){
      List<Integer> prefix = new ArrayList<>(nums);
      for(int i = 1; i < prefix.size(); ++i)
        prefix.set(i, prefix.get(i) + prefix.get(i-1));
      return prefix;
    }
}
/*
System.out: 
Nums:   [1, 2, 3, 4, 5, 6, 7, 8, 9]
Prefix: [1, 3, 6, 10, 15, 21, 28, 36, 45]
*/

Here, in the prefixList function, the nums list is first cloned, but then there is the iterative operation performed on it, where the value on index i relies on index i-1 (i.e. order of execution is required). Then this value is returned.

What would this look like in a functional language (Haskell, Lisp, etc.)? I have been learning about monads and think they may be relevant here, but my understanding is still not great.

ANSWER

Answered 2022-Mar-07 at 21:17

This is not an index-heavy operation, in fact you can do this with a one-liner with scanl1 :: (a -> a -> a) -> [a] -> [a]:

prefixList = scanl1 (+)

indeed, for the list of Nums, we get:

Prelude> prefixList [1 .. 9]
[1,3,6,10,15,21,28,36,45]

scanl1 takes the first item of the original list as initial value for the accumulator, and yields that. Then each time it takes the accumulator and the next item of the given list, and sums these up as new accumulator, and yields the new accumulator value.

Often one does not need indexing, but enumerating over the list is sufficient. Imperative programming languages often work with for loops with indexes, but in many cases these can be replaced by foreach loops that thus do not take the index into account. In Haskell this also often helps to make algorithms more lazy.

If you really need random access lookups, you can work with data structures such as defined in the array and vector packages.

Source https://stackoverflow.com/questions/71387267

QUESTION

Keras AttributeError: 'Sequential' object has no attribute 'predict_classes'

Asked 2022-Mar-23 at 04:30

Im attempting to find model performance metrics (F1 score, accuracy, recall) following this guide https://machinelearningmastery.com/how-to-calculate-precision-recall-f1-and-more-for-deep-learning-models/

This exact code was working a few months ago but now returning all sorts of errors, very confusing since i havent changed one character of this code. Maybe a package update has changed things?

I fit the sequential model with model.fit, then used model.evaluate to find test accuracy. Now i am attempting to use model.predict_classes to make class predictions (model is a multi-class classifier). Code shown below:

model = Sequential()
model.add(Dense(24, input_dim=13, activation='relu'))
model.add(Dense(18, activation='relu'))
model.add(Dense(6, activation='softmax'))
model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])

-

history = model.fit(X_train, y_train, batch_size = 256, epochs = 10, verbose = 2, validation_split = 0.2)

-

score, acc = model.evaluate(X_test, y_test,verbose=2, batch_size= 256)
print('test accuracy:', acc)

-

yhat_classes = model.predict_classes(X_test)

last line returns error "AttributeError: 'Sequential' object has no attribute 'predict_classes'"

This exact code was working not long ago so struggling a bit, thanks for any help

ANSWER

Answered 2021-Aug-19 at 03:49

This function were removed in TensorFlow version 2.6. According to the keras in rstudio reference

update to

predict_x=model.predict(X_test) 
classes_x=np.argmax(predict_x,axis=1)

Or use TensorFlow 2.5 or later.

If you are using TensorFlow version 2.5, you will receive the following warning:

tensorflow\python\keras\engine\sequential.py:455: UserWarning: model.predict_classes() is deprecated and will be removed after 2021-01-01. Please use instead:* np.argmax(model.predict(x), axis=-1), if your model does multi-class classification (e.g. if it uses a softmax last-layer activation).* (model.predict(x) > 0.5).astype("int32"), if your model does binary classification (e.g. if it uses a sigmoid last-layer activation).

Source https://stackoverflow.com/questions/68836551

QUESTION

Getting error 'digital envelope routines', reason: 'unsupported', code: 'ERR_OSSL_EVP_UNSUPPORTED'

Asked 2022-Mar-05 at 09:54

I got this error when learning Next.js, using npx create-next-app command according to site documentation here https://nextjs.org/docs/api-reference/create-next-app. Everything works until I start the server,

Error stack:

$ npm run dev

> devto-clone@0.1.0 dev
> next dev

ready - started server on 0.0.0.0:3000, url: http://localhost:3000
info  - Using webpack 5. Reason: Enabled by default https://nextjs.org/docs/messages/webpack5
Error: error:0308010C:digital envelope routines::unsupported
    at new Hash (node:internal/crypto/hash:67:19)
    at Object.createHash (node:crypto:130:10)
    at BulkUpdateDecorator.hashFactory (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:138971:18)
    at BulkUpdateDecorator.update (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:138872:50)
    at OriginalSource.updateHash (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack-sources3\index.js:1:10264)
    at NormalModule._initBuildHash (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68468:17)
    at handleParseResult (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68534:10)
    at C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68628:4
    at processResult (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68343:11)
    at C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68407:5
Error: error:0308010C:digital envelope routines::unsupported
    at new Hash (node:internal/crypto/hash:67:19)
    at Object.createHash (node:crypto:130:10)
    at BulkUpdateDecorator.hashFactory (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:138971:18)
    at BulkUpdateDecorator.update (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:138872:50)
    at OriginalSource.updateHash (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack-sources3\index.js:1:10264)
    at NormalModule._initBuildHash (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68468:17)
    at handleParseResult (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68534:10)
    at C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68628:4
    at processResult (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68343:11)
    at C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68407:5
node:internal/crypto/hash:67
  this[kHandle] = new _Hash(algorithm, xofLen);
                  ^

Error: error:0308010C:digital envelope routines::unsupported
    at new Hash (node:internal/crypto/hash:67:19)
    at Object.createHash (node:crypto:130:10)
    at BulkUpdateDecorator.hashFactory (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:138971:18)
    at BulkUpdateDecorator.update (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:138872:50)
    at OriginalSource.updateHash (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack-sources3\index.js:1:10264)
    at NormalModule._initBuildHash (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68468:17)
    at handleParseResult (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68534:10)
    at C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68628:4
    at processResult (C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68343:11)
    at C:\xampp\htdocs\devto-clone\node_modules\next\dist\compiled\webpack\bundle5.js:68407:5 {
  opensslErrorStack: [ 'error:03000086:digital envelope routines::initialization error' ],
  library: 'digital envelope routines',
  reason: 'unsupported',
  code: 'ERR_OSSL_EVP_UNSUPPORTED'
}

Node.js v17.0.1

package.json :

{
  "name": "devto-clone",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  },
  "dependencies": {
    "next": "11.1.2",
    "react": "17.0.2",
    "react-dom": "17.0.2"
  },
  "devDependencies": {
    "eslint": "7.32.0",
    "eslint-config-next": "11.1.2"
  }
}

ANSWER

Answered 2021-Nov-24 at 21:38

I found this solution https://github.com/webpack/webpack/issues/14532

if using bash just run NODE_OPTIONS=--openssl-legacy-provider before any command
adding NODE_OPTIONS=--openssl-legacy-provider to package.json

"scripts": {
   "start": "SET NODE_OPTIONS=--openssl-legacy-provider && react-scripts start",
   "build": "SET NODE_OPTIONS=--openssl-legacy-provider && react-scripts build"
 },

Edit

In my case, I'm using Nodejs 17.0.1 version and causing this error.

Firstly I'm using this command export NODE_OPTIONS=--openssl-legacy-provider before any command in GitBash Windows to fix this issue.

But, I think it's not an efficient way, so what I do is :

Uninstall Nodejs 17.0.1
Install it again Nodejs 16.13.0 version
I'm facing error another error when I start the server using "yarn serve" (another of my exiting Vuejs project), I don't remember what is this, but after I run "yarn" and "yarn serve", everything works now as I accept

Source https://stackoverflow.com/questions/69719601

QUESTION

Vue 3 passing array warning: Extraneous non-props attributes were passed to component but could not be automatically inherited

Asked 2022-Feb-26 at 21:48

please, I'm learning a VueJS 3 and I have probably begineer problem. I have warn in browser developer console like this one:

The Message is:

[Vue warn]: Extraneous non-props attributes (class) were passed to component but could not be automatically inherited because component renders fragment or text root nodes.

I'm passing array of objects to the child Component. In my parent views/Home.vue compoment I have this implemenation:

<template>
  <div class="wrapper">
    <section v-for="(item, index) in items" :key="index" class="box">
      <ItemProperties class="infobox-item-properties" :info="item.properties" />
    </section>
  </div>
</template>
<script>
import { ref } from 'vue'
import { data } from '@/data.js'
import ItemProperties from '@/components/ItemProperties.vue'

export default {
  components: {
    ItemDescription,
  },
  setup() {
    const items = ref(data)

    return {
      items,
    }
  },
</script>

In child compoment components/ItemProperties.vue I have this code:

<template>
  <div class="infobox-item-property" v-for="(object, index) in info" :key="index">
    <span class="infobox-item-title">{{ object.name }}:</span>
    <span v-if="object.type === 'rating'">
      <span v-for="(v, k) in object.value" :key="k">{{ object.icon }}</span>
    </span>
    <span v-else>
      <span>{{ object.value }}</span>
    </span>
  </div>
</template>

<script>
export default {
  props: {
    info: {
      type: Array,
      required: false,
      default: () => [
        {
          name: '',
          value: '',
          type: 'string',
          icon: '',
        },
      ],
    },
  },
}
</script>

It doesn't matter if I have default() function or not. Also doesn't matter if I have v-if condition or not. If I have cycle in the Array, I got this warning

Data are in data.js file. The part of file is here:

export const data = [
  {
    title: 'White shirt',
    properties: [
      { name: 'Material', value: 'Cotton', type: 'string', icon: '' },
      { name: 'Size', value: 'M', type: 'string', icon: '' },
      { name: 'Count', value: 4, type: 'number', icon: '' },
      { name: 'Absorption', value: 4, type: 'rating', icon: '💧' },
      { name: 'Rating', value: 2, type: 'rating', icon: '⭐️' },
      { name: 'Confort', value: 2, type: 'rating', icon: '🛏' },
      { name: 'Sleeves', value: 'Short', type: 'string', icon: '' },
      { name: 'Color', value: 'White', type: 'string', icon: '' },
    ],
  },
]

PS: Application works but I'm afraid about that warning. What can I do please like right way?

I will be glad for any advice. Thank you very much.

ANSWER

Answered 2021-Aug-16 at 13:32

The ItemProperties component has multiple root nodes because it renders a list in the root with v-for.

Based on the class name (infobox-item-properties), I think you want the class to be applied to a container element, so a simple solution is to just add that element (e.g., a div) in your component at the root:

// ItemProperties.vue
<template>
  <div>
    <section v-for="(item, index) in items" :key="index" class="box">
    ...
    </section>
  </div>
</template>

demo

Source https://stackoverflow.com/questions/68803137

QUESTION

TypeError: match.loader.options.plugins is not a function

Asked 2022-Feb-24 at 05:03

I am trying to use tailwindCSS in a ReactJS app

These are the scripts commands in package.json file

  "scripts": {
    "start": "craco start",
    "build": "craco build",
    "test": "craco test",
    "eject": "react-scripts eject"
  }

This is my craco.config.js

module.exports = {
    style: {
        postcss: {
            plugins: [
                require('tailwindcss'),
                require('autoprefixer'),
            ],
        },
    },
}

When I am used npm run start command, I am facing this error

TypeError: match.loader.options.plugins is not a function
    at extendsPostcss (C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\style\postcss.js:54:51)
    at overrideLoader (C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\style\postcss.js:97:9)
    at C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\style\postcss.js:118:13
    at Array.forEach (<anonymous>)
    at overridePostcss (C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\style\postcss.js:117:17)
    at overrideStyle (C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\style\style.js:9:25)
    at mergeWebpackConfig (C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\merge-webpack-config.js:77:30)
    at overrideWebpackDev (C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\lib\features\webpack\override.js:11:36)
    at C:\Development\Open Source\Learning Hub\react\node_modules\@craco\craco\scripts\start.js:27:5

Things that I have tried :

Reinstall node_modules

Got this error, when I tried to do that

$ npm i @craco/craco
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: first-react-app@0.1.0
npm ERR! Found: react-scripts@5.0.0
npm ERR! node_modules/react-scripts
npm ERR!   react-scripts@"5.0.0" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer react-scripts@"^4.0.0" from @craco/craco@6.4.3
npm ERR! node_modules/@craco/craco
npm ERR!   @craco/craco@"*" from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.

ANSWER

Answered 2021-Dec-18 at 22:00

It looks like the Tailwind configuration from CRACO is not needed anymore.

https://github.com/facebook/create-react-app/issues/11771#issuecomment-997217680

Look at Tailwind 3.0 install steps: https://tailwindcss.com/docs/guides/create-react-app

Source https://stackoverflow.com/questions/70403417

QUESTION

Group and create three new columns by condition [Low, Hit, High]

Asked 2022-Feb-10 at 16:22

I have a large dataset (~5 Mio rows) with results from a Machine Learning training. Now I want to check to see if the results hit the "target range" or not. Lets say this range contains all values between -0.25 and +0.25. If it's inside this range, it's a Hit, if it's below Low and on the other side High.

I now would create this three columns Hit, Low, High and calculate for each row which condition applies and put a 1 into this col, the other two would become 0. After that I would group the values and sum them up. But I suspect there must be a better and faster way, such as calculate it directly while grouping. I'm happy for any idea.

Data

import pandas as pd

df = pd.DataFrame({"Type":["RF", "RF", "RF", "MLP", "MLP", "MLP"], "Value":[-1.5,-0.1,1.7,0.2,-0.7,-0.6]})

+----+--------+---------+
|    | Type   |   Value |
|----+--------+---------|
|  0 | RF     |    -1.5 | <- Low
|  1 | RF     |    -0.1 | <- Hit
|  2 | RF     |     1.7 | <- High
|  3 | MLP    |     0.2 | <- Hit
|  4 | MLP    |    -0.7 | <- Low
|  5 | MLP    |    -0.6 | <- Low
+----+--------+---------+

Expected Output

pd.DataFrame({"Type":["RF", "MLP"], "Low":[1,2], "Hit":[1,1], "High":[1,0]})

+----+--------+-------+-------+--------+
|    | Type   |   Low |   Hit |   High |
|----+--------+-------+-------+--------|
|  0 | RF     |     1 |     1 |      1 |
|  1 | MLP    |     2 |     1 |      0 |
+----+--------+-------+-------+--------+

ANSWER

Answered 2022-Feb-10 at 16:13

You could use cut to define the groups and pivot_table to reshape:

(df.assign(group=pd.cut(df['Value'],
                        [float('-inf'), -0.25, 0.25, float('inf')],
                        labels=['Low', 'Hit', 'High']))
   .pivot_table(index='Type', columns='group', values='Value', aggfunc='count')
   .reset_index()
   .rename_axis(None, axis=1)
)

Or crosstab:

(pd.crosstab(df['Type'],
             pd.cut(df['Value'],
                    [float('-inf'), -0.25, 0.25, float('inf')],
                    labels=['Low', 'Hit', 'High'])
             )
   .reset_index().rename_axis(None, axis=1)
 )

output:

  Type  Low  Hit  High
0  MLP    2    1     0
1   RF    1    1     1

Source https://stackoverflow.com/questions/71068392

QUESTION

What should the result be when assigning a variable to a reference to itself, in-between modified and then returned by a function call?

Asked 2022-Feb-02 at 00:42

#include <iostream>

int& addOne(int& x)
{
    x += 1;
    return x;
}

int main()
{
    int x {5};
    addOne(x) = x;
    std::cout << x << ' ' << addOne(x);
}

I'm currently in the middle of learning about lvalues and rvalues and was experimenting a bit, and made this which seems to be getting conflicting results. https://godbolt.org/z/KqsGz3Toe produces an out put of "5 6", as does Clion and Visual Studio, however https://www.onlinegdb.com/49mUC7x8U produces a result of "6 7"

I would think that because addOne is calling x as a reference, it would explicitly change the value of x to 6 despite being called as an lvalue. What should the correct result be?

ANSWER

Answered 2022-Feb-02 at 00:42

Since C++17 the order of evaluation is specified such that the operands of = are evaluated right-to-left and those of << are evaluated left-to-right, matching the associativity of these operators. (But this doesn't apply to all operators, e.g. + and other arithmetic operators.)

So in

addOne(x) = x;

first the value of the right-hand side is evaluated, yielding 5. Then the function addOne is called and it doesn't matter what it does with x since it returns a reference to it, to which the right-hand value 5 is assigned.

Formally, evaluating the right-hand side first means that we replace the lvalue x by the (pr)value it holds (lvalue-to-rvalue conversion). Then we call addOne(x) to modify the object that the lvalue x refers to.

So, imagining temporary variables to hold the results of the individual evaluations, the line is equivalent to (except for extra copies introduced by the new variables, which don't matter in the case of int):

int t = x;
int& y = addOne(x);
y = t; // same as x = t, because y will refer to x

Then in the line

std::cout << x << ' ' << addOne(x);

we first evaluate and output x, resulting in 5, and then call addOne, resulting in 6.

So the line is equivalent to (simplified, knowing that operator<< will return std::cout again):

int t1 = x;
std::cout << t1 << ' ';
int t2 = addOne(x);
std::cout << t2;

The output 5 6 is the only correct one since C++17.

Before C++17, the evaluation order of the two sides of the assignment operator was unsequenced.

Having a scalar modification unsequenced with a value computation on the same scalar (on the right-hand side of your assignment) causes undefined behavior normally.

But since you put the increment of x into a function, an additional rule saying that the execution of a function body is merely indeterminately sequenced with other evaluations in the calling context saves this. It means that the line wont have undefined behavior anymore, but the order in which the evaluations of the two sides of the assignment happen could be either left-first or right-first.

This means we won't know whether x is evaluated first and then addOne(x) or the other way around.

Therefore after the line, x may be 5 or 6.

6 would be obtained if the evaluation happened equivalently to

int& y = addOne(x);
int t = x;
y = t;

Then in the line

std::cout << x << ' ' << addOne(x);

pre-C++17 the same issue applied. The evaluations of the arguments to << were indeterminately sequenced, rather than left-to-right and so addOne(x) could be evaluated before the left-hand x, i.e. in addition to the previous order, the evaluation could also be equivalent to

int t2 = addOne(x);
int t1 = x;
std::cout << t1 << ' ' << t2;

In this case x is first incremented and then its new value is printed twice.

Therefore possible program output could be either of the following:

(Technically the int t2 = addOne(x) are two evaluations: One call to addOne returning a reference and then the lvalue-to-rvalue conversion. These could happen interleaved with the other evaluations, but this doesn't give any new program outputs.)

You can specify to use C++17 (or newer versions like C++20) with the -std=c++17 flag to the compiler if you are using GCC or Clang and /std:c++17 if you are using MSVC. Which standard version is chosen by-default depends on the compiler and compiler version.

Source https://stackoverflow.com/questions/70909321

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