Type punning is real fun to mess around with.

Remember that coffee intro? :P

I finally understood better what was done in that Quake video

But Carmack said "SIMD is not a useful thing", and now we use glm instead of bitwise magic. :D

Carmack is a genius

​@@magellan124 carmack didn't invent it, he found out about it from someone else

@@softed who?

He didn't mention undefined behavior in this video. A lot of code here has undefined behavior. You need to walk on a thin line if you want to write code like this and avoid undefined behavior. I have read Joe Zbiciak's answers and comments on Quora about what is defined and what is undefined (at least for C, usually what is true for C is also true for C++ but here we are on a thin ice territory). If you don't know by heart what is and what isn't undefined behavior when it comes to things like this you can't guess it.

I do this regularly and I know exactly what you mean!

This is my favourite comment. If someone asks me if I have seen a good comment before, I'm going to refer them here.

​@@jakub7321 This is my favorite sub-comment, which points to the favorite comment. If anyone asks me about why C++ is so wonderful, I'll tell them about pointers and point to this sub-comment, which sill refer to the parent comment.

@@mykolatetiuk6661 I really don't want to prove something but here is a C# equivalent code. Maybe someone doesn't even know that you could do that in C# too ;-) using System; class Program { struct Entity { public int x, y; } unsafe static void Main() { Entity e = new Entity{x = 5, y = 8}; int* position = (int*)&e; int y = *(int*)((byte*)&e + 4); Console.WriteLine(position[0] + ", " + position[1]); Console.WriteLine(y); Console.ReadLine(); } }

In programming you have to construct everything yourself, I thought I knew that... Unless of course there's a preconstructed library.

Variables can have multiple "meanings" depending on the datatypes they are cast to. Puns, you see?

I think you mean, utterly "disappointered" ;) Sorry...

idk why everyone thinks that "beginners" just go around type punning shit for no reason. what do you think they're doing? you think static typing is so difficult a concept to grasp that, instead of just using the type system like they're supposed to, novice programmers just think it's a good idea to store all their scalars as an int64 and fucking type pun into them? two year old comment nigga ass.

wrggg

@@loli42 Maybe someone who doesn't even know what a type pun is (like me) would try to use % on a double by first using a long long then casting that way too big long long into a double without losing a bunch of data. As far as I know, cpp doesn't give warnings for bad or unnecessary casting.

@@puppergump4117 that's not type punning, it's casting, and c++ compilers most certainly do emit warnings for implicit narrowing conversions because msvc won't shut the fuck up about it

@@loli42 I obviously know that. Which is why I explicitly said 'casting'. After casting loses double data, I try type punning. And from MY experience, there were no warnings.

all the examples are UB

Both are not legal ways to type pun in C or C++. So. They are at least similar in that way.

You refer to it like its some popular joke not some random line of code burried within a game's source code... I love it XD

@@SandFoxling it is a popular joke, what do you mean? The quake 3 fast inverse square root code is legendary. (For the comments more than the actual code)

​@@totallynuts7595 I figured, I guess I'm not old enough... I have read 'masters of doom' but that's about the extent of my knowledge on the early days of ID and their legendary feats. I guess you still would have to call that joke within a specific circle to actually cast it into a popular type.

@@SandFoxling i'm not that old either, compared to the games. I just like Doom and Quake

I should of asked for her namespace because now i have a STD

Jp Silver epic 😂😂

Type puns here

@Jp Silver , I *c* what you did there. 😁

xD xD

The whole experience of programming in C can be summarized as undefined behaviour. As far as I remember alignment isn't really an issue, of course it would be if you wrote the code that was demonstrated, but there are easy ways to deal with alignment if you actually want to dive into this unique flavour of BDSM.

@@OFfic3R1K The best way to legally type pun in C++ is to use memcpy (which is legal since a new object is created. This means the strict aliasing rules aren't violated). We do get std::bit_cast though which will allow for type punning casts and it can be used in constexpr situations.

​@@lincolnsand5127 @OFfic3RiK Great discussion! As a newbie I have a question. If our code is absolutely free of alignment and Endian problems, could type punning still cause unexpected errors? I saw a stack overflow example claiming that, when compiler optimization is in place, under strict aliasing rule, the compiler might assume two pointers of different types point to different places, and thus decide the writes via the 1st pointer do not affect the 2nd pointer and its pointed value, so it generates machine code which may not register-load the 2nd pointed value in time, and thus lead to catastrophe. However some other people were saying the post was wrong. Do you think this as an legitimate issue?

@@wusuoliu5431 Well. It depends. gcc and clang have a flag called -fno-strict-aliasing. If you don't use that flag, compiler optimizations might break your code. If you have the flag, *only* hardware-specific things will (e.g. some architectures don't allow unaligned loads).

Try to think that when you cast pointers or a variable adress (&var) you are just saying to the compiler "Hey use this memory adress to read or write and trust me that everything will be fine". You can have 10 different vars/pointers pointing, reading and writting to that same memory space that the compiler doesn't care if you this C-Style casting. But if you do a mistake you'll have undifined behaviour or memory leaks will emerge.

wdym by similar

What are you doing on this video if you're new to C++? Go watch older videos lol

So in your opinion if you watched all of Cherno's videos you are no longer a beginner at C++?

pointers were great, but I've almost never used any pointers since c++11 and STL, because they tend to generate bugs and crash programs (if you don't handle them well). pointer-related garbage collection is such a pain.

garbage collection? i thought that was only a thing in managed languages like c# (i think that is what you call them). I don't see how garbage collection is a Thing in c++ (unless you run that managed, which i think is somehow possible), i mean that is also a big reason why i came to c++ ... so i can manage memory myself, and not worry about constructing any referance type objects (so heap allocated) in any part of my programm that gets run quite often. (so game a loop, in my case that was block placeing) it was just too annoying to deal with EDIT: removed a word "a" which was somewhere it shouldn't have been XD

yeah I think I misused the word 'garbage collection'. I don't mean that C++ has a garbage collector, only that the syntax of C++11 completely (unless you have to deal with some legacy code) makes using C's malloc(), free(), or C++98's 'new' and 'delete' unnecessary. All those works are done in the built-in containers and classes, so it pretty much behaves like a 'garbage collector' from a programmer's perspective. (not a real garbage collector thought, more like an API-level garbage collection that prevents memory leak)

With the same potential of a crash because you might access memory that doesn't exist.

Not always, but usually yes. ;-) Endianness is not an operating system thing, so accessing memory as int pointer to index the int struct elements should work the same on Linux x86 too and on Sparc, MIPS, etc too without worrying these. But this is only true, if you cast elements back to the types they originally was and if you work with the data in the same program only. The problem starts, when these data leave your program in any way. If you serialize an int, send the chars over a network into a different (endianness) machine, then you read it back there and cast back to an int. Then it will be backwards. This is the reason why there are htons() and nthos() functions exists for TCP/IP networking. The network byte order is standardized, and if the system you compile on is in the same byteorder then these functions do nothing, if it is different then they swap the data. Another issue is that sizeof(int) is implementation-defined. It could very probably happen that if you send ints from a PC to a 8-bit microcontroller where int could be just 8-bits then you also have a problem. Theoretically you could even have a problem, when you save data to a file, and open it on the exact same machine and OS, but with a different program, which might be compiled with a different compiler. This is why one should avoid using int, and use fixed size types like uint32_t instead. Another issue is memory alignment and structs. Some architectures, ARM for example doesn't like unaligned memory access, so an 32-bit integer should reside on 4 byte address boundary only. So if you have a struct { char, uint32_t } then you have 8 byte allocated, the first byte is a char, 3 byte padding, then 4 bytes of int. If you serialize this struct by indexing it's memory you may expect that you have 5 bytes of data, but instead you have 8, because of the padding. This is a problem when you want to map a struct to a hardware register or some kind of network data. Some compilers have a possibility to tell them to generate packed-struct to avoid padding. Non-standard, non-portable, of course. attribute((packed)) in GCC, #pragma pack in others, etc... And if the target CPU really can't do unaligned access, then the compiler will generate two aligned reads for that unaligned int then shifts the bits to assemble it for you. Performance issue... All of this can happen and this is why this considered dangerous and you should not do it unless you are develop a low-level system in a specific environment and you know exactly what are you doing.

Yeah, this is not portable!

It Cracks! Godbolt has his own channel, really cool, check him out!

Newbies should get to know it, that's what I meant.

still i agree w/u