Pratique du Shadowing: you will never ask about pointers again after watching this video - Apprendre l'anglais à l'oral avec la vidéo
Création de la leçon...
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One of the hardest things for new programmers to learn is pointers.
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Whether it's pointers by themselves, pointers that point to arrays, or pointers that point to pointers, Something about this concept just drives people crazy.
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And if you're a new programmer, well, you're not alone.
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I was one of those people when I learned C back in the day, and like you, I was eager to understand.
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In this video, I'll show you what a pointer is so you can fully understand how they work, the syntax of pointers so you can easily read them,
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and finally, why everyone cares so much about pointers and what they're used for.
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Before we start, if you're new here, hit that subscribe button and while you're at it leave a like.
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I put out videos demystifying topics like this and much more on a weekly basis.
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What is a pointer?
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The question that's been asked since the beginning of time.
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well, maybe not that long, but computer science students have been asking this question for a while.
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Pointers are not that complicated, and let me show you why.
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To understand what a pointer is, we need to first understand how memory works.
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So here I've laid out an example of memory.
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Memory in our example has two features: an address, and a value.
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The address is the location of the memory, meaning where that memory lives.
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And the value of that memory is the data stored at that location, meaning what memory lives there.
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So for example, if I put a four here, What does that mean?
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All that means is that the value 4 lives at location hex 1000.
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Easy.
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And the notation in C, for example, may be int x equals four, which gets allocated to that memory on the stack, and now that number lives there.
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So what happens now if at another location I put the number hex 1000 at address hex 1004?
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I've just created a pointer.
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You may be thinking, low level learning, how is this possible?
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That's just a number at a location.
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Well guys, that's the secret.
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A pointer is just a value that happens to be an address.
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Mind blown.
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By setting the value of one variable equal to the address of another, that variable now points to the other.
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For new programmers, though, most of the time, that isn't as easy as it seems.
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One of the most common issues new programmers have with pointers is the syntax used to create them.
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The combination of stars and ampersands and arrows and more stars creates a lot of confusion, so let's break this down using our previous example.
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In our last example, we made an integer x whose value was 4 at location hex 1000.
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After that, we made a pointer that lived at address hex 1004, whose value was $1000.
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So how do we do that in C?
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We can do that using two lines of code, and I'll break them down part by part.
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The first line is int x equals four.
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This line is pretty straightforward.
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The first part, integer, is the type of the variable, which is 4 bytes wide, and this will matter later in the video.
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The second part is the name.
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Nothing special here, just the variable name x.
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And then after that, we put an equal sign, which when describing C, we can verbalize the equal sign to is C set to.
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Finally, the value 4.
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So the final sentence we've come up with is, Integer whose name is X is set to the value 4.
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Okay.
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Easy part over, next is the hard part.
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To make a pointer to x like we did in our example, I would say the following line of C: int *px is equal to ampersand x.
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Now I know that sounds pretty crazy, a little scary, Let's break it down piece by piece.
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From left to right, we can see the type again, starting with int.
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But next we see the dreaded Asterisk.
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What does that mean?
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When an asterisk is placed next to a type, it modifies the type, meaning that our variable is now a pointer to an integer.
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So our variable here points to a four byte value.
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Next, the variable's name which is Px or pointer to x, You can name it whatever you want, but this is a good habit using "P" to denote that it's a pointer.
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and then after that are equal sign, which again means is set to.
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Ah, and then the next dreaded character, the Ampersand.
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Whenever you see an ampersand just think in your head the address of.
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So this means the address of x.
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Our final sentence here is, Int pointer.
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P X is set to the address of X.
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So, what does this do for us?
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Well now by using the pointer, we have a way of accessing x by reference instead of by value.
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So for example, if we wanted to copy the value of x to a new variable using that pointer, we could do that pretty easily with this new bit of code.
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We'll say that int y equals *px.
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Now what is this code doing?
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Let's break it down.
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Again, y, just like x, is a normal integer, so no pointers yet.
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We say that Y is set to, using that equal sign, uh oh, the asterisk again.
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Remember how last time I said when we see an asterisk, it's used to modify a type if a type is near it?
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Well, here there is no type.
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When it's used alone this way, the asterisk is referred to as a "d" reference.
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The dereference means go to the address pointed to by the pointer and grab that value.
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So, because px points to x, The dereference will go and grab that value and it will set Y equal to x.
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So when reverbalizing C, when you see an asterisk by itself, you can say "the thing pointed to by."
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This would mean that the final verbalization of this line of C is
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integer y is set to the thing pointed to by p x.
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By doing this, we can pass around X by reference instead of value.
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And why that matters, I'll explain in the next part of the video.
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The final concept that could use people the most when learning about pointers is why does anyone use them?
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The syntax is confusing, my programs crash all the time when I use them, why does anyone bother?
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Well, the answer is because we have to.
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To avoid making code that is impossible to read or unscalable, we break down functions based on the action that they perform,
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So here I have a small snippet of C where I have a function that updates the age of a person structure.
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The problem is that the structure I'm editing is not in scope of the editing function.
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To get around this, we pass the struct by reference so that now the pointer to the structure
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is in scope of update struct and can therefore be edited.
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Using pointers like this keeps our code clean and understandable while reducing the amount of space that we use by not copying.
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Another reason that pointers are inevitable when coding in C is the idea of using static versus dynamic memory allocation.
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static allocation is typically a variable that goes onto the stack, a place that is always in scope for the function that is running it.
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However, when you're using dynamic allocations that come from the heap through malloc or sbreak or other kinds of memory allocators,
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you are going to get a pointer to memory that is out of scope.
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If you ever want to be able to use this kind of memory, you need to know how pointers work.
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The primary difference between dynamic and static allocations is
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that static allocations are things
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that are known to have a fixed size at compile time
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whereas dynamic allocations can be changed in size as the program runs.
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Here you see I allocate a string of 100 bytes to be pulled from the heap
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But that 100 bytes could have come from a user input or something else.
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If you're having a hard time with C, don't be discouraged.
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Pointers do take a minute to master, but once you get them, you'll know it and you'll feel like a real low level wizard when you do.
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Guys, I had a fun time making this video.
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If you enjoyed this, do me a favor, hit like, hit subscribe, and I'll see you next week.
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Take care.
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Vocabulaire et conseils d’expression pour cette leçon
Cette vidéo contient 103 phrases et 1434 mots à répéter en shadowing. La partie parlée dure 7:59. Le locuteur parle vite, environ 180 mots par minute : attendez-vous à des liaisons et à des sons réduits. Seuls 81 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
15 mots moins courants de la vidéo, avec leur prononciation et leur sens :
- pointer /ˈpɔɪn.təɹ/ (nom) — aiguille. One who points.
- variable [ˈvæɹ.i.ə.bl̩] (adjectif) — variable. Able to vary or be varied.
- allocation /ˌæl.əˈkeɪ.ʃən/ (nom) — allocation. The process or procedure for allocating things, especially money or other resources.
- dynamic /daɪˈnæm.ɪk/ (adjectif) — dynamique. Changing; active; in motion.
- scope /skəʊp/ (nom) — portée. The breadth, depth or reach of a subject; the extent of applicability or relevance; a domain, purview or remit.
- static /ˈstæt.ɪk/ (adjectif) — statique. Unchanging; that cannot or does not change.
- programmer /ˈpɹoʊɡɹæmɚ/ (nom) — programmeur, programmeuse. One who writes computer programs.
- edit /ˈɛdɪt/ (verbe) — modifier, corriger. To change a text, or a document.
- syntax /ˈsɪn.tæks/ (nom) — syntaxe. A set of rules that govern how words are combined to form phrases and sentences.
- stack /stæk/ (nom) — pile. A large pile of hay, grain, straw, or the like, larger at the bottom than the top, sometimes covered with thatch.
- subscribe /səbˈskɹaɪb/ (verbe) — abonner, s'abonner. To write (one’s name) at the bottom of a document; to sign (one's name).
- modify /ˈmɑ.dɪˌfaɪ/ (verbe) — modifier. To change part of.
- dread /dɹɛd/ (nom) — crainte. Great fear in view of impending evil; fearful apprehension of danger; anticipatory terror.
- topic /ˈtɑpɪk/ (nom) — sujet, thème. A subject; a theme; a category or general area of interest.
- complicated /ˈkɑm.plɪˌkeɪ.tɪd/ (adjectif) — compliqué, alambiqué. Difficult or convoluted.
Les verbes à particule que vous entendrez
- break down (verbe) — tomber en panne. To stop functioning.
- come up with (verbe) — inventer, imaginer. To manage to produce, deliver, or present (something) by inventing, creating, thinking of, or obtaining it.
- do in (verbe) — tuer, zigouiller. To kill or end; to defeat.
Prononciation à surveiller
Le locuteur utilise 20 contractions et formes réduites, comme you're, I'll, I've. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « sh » et « zh »: allocation /ˌæl.əˈkeɪ.ʃən/, confusion /kənˈfjuːʒən/, notation /noʊˈteɪʃən/
- Mots longs — placez bien l’accent: allocation /ˌæl.əˈkeɪ.ʃən/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, inevitable /ɪˈnɛvɪtəbəl/, allocator /ˈæl.ə.keɪ.tə/, demystify /diːˈmɪstɪfaɪ/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme pointer, variable, allocation.
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | been asked · is set · is placed |
| Present perfect have/has + participe passé — une action passée qui compte encore maintenant | I've laid · I've just created · we've come |
| Propositions relatives who / which + proposition — une précision sur une personne ou une chose | variable, which is · name which is |
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.