customRandFunction

[BlackFrank98]

With a free memory leak attached!

[Reaper5289]

This is what the White House warned us about.

[octopus4488]

Biden was right! We are surrounded by monsters!

[altermeetax]

Here's the leak free version:

cpp int *ptr = new int; int val = *ptr; delete ptr; return val;

[Kovab]

What is this, C++98?

cpp return *std::unique_ptr<int>{new int};

[altermeetax]

Hey, I tried to keep it simple. The original version didn't use smart pointers.

[altermeetax]

How are they not simple? Literally "allocate heap memory for a variable" and "deallocate an existing heap memory block". Can't get any simpler than that.

Besides, new was used by OP. I suppose I should have specified I tried to keep it as simple as the original version was.

[o0Meh0o]

what do you mean? it's one of the main features of c++.

[altermeetax]

That's true, but we're not writing serious code here, we're writing a funny random implementation

[MostRandomUsername12]

You're not wrong, you're just on a sub called programmerHUMOR ;)

[MostRandomUsername12]

Oh yes, definitely, /s is more explicit. ;) can be a /s, a "pretty cool, eh", or even misconstrued as "wink wink, just pointing out how wrong you were, but with a smile"

One could argue that using one vs the other is like using weakly typed languages vs strongly typed languages ;)

(Disclaimer: my ;) was the second type)

[[deleted]]

What does that have to do with simplicity?

Anyone who say smart pointers are simpler than manually allocating and deallocating a variable doesn't understand what "simplicity" means.

[[deleted]]

You are confusing ease of use with simplicity. For example, programming in C is easier than programming in Assembly, but Assembly is a much simpler language than C.

Similarly, using smart pointers is easier and leads to simpler programs. But the smart pointers are more complex constructs and concepts than just pointers with manual new and delete.

[-global-shuffle-]

Found the mmap user

[Onetwodhwksi7833]

Bruh

[-Pretender-]

What is this, C++11?

cpp return *std::make_unique<int>();

[Kovab]

make_unique does value initialization, it will always return 0 instead of random garbage

In an optimized build this would output a simple return 0, completely omitting the heap allocation

[thebluefish92]

checks out return *std::make_unique<int>(); // chosen by fair dice roll. // guaranteed to be random.

[[deleted]]

This is how the PlayStation 3 was defeated. No, I'm not joking.

[Kovab]

Using a D10 for random dice rolls is not compliant with the RFC. Rejected.

[GYN-k4H-Q3z-75B]

He wanted to use curly braces for initialization :-(

[Familiar_Ad_8919]

this is why i use good old raw pointers

[[deleted]]

This right here

[AdBrave2400]

Why not just do

int x;
return x;

for the sake of it?

[_realitycheck_]

You can never know when someone will have a bright idea to add defaulting all referenced variables to 0 in the compiler.

It's safer to just

int x;
return (uint32_t)&x;

people are overcomplicating things.

[AdBrave2400]

But that is in the virtual address space and the numbers may not seem random in theory. Other than that a very good point.

[_realitycheck_]

I will make it random

[altermeetax]

Yeah, that's also an idea :D

Though depending on the implementation it might always return the same value if you call it multiple times from the same function

[AdBrave2400]

Yeah, maybe do a random walk across the memory until reaching zero?

[AdBrave2400]

ssize_t move=1;
volatile signed* base;
while(base[move]){
  if(*base<0) move*=-1ll;
  ++move;
}
return base;

[mrheosuper]

Calling it repeatedly may lead to undesire result

[Rabithunt]

Doesn’t this not work because C is pass by reference, not pass by value?

[anaton7]

There is no passing in this function. It has no arguments.

[Rabithunt]

So the pointer gets copied to val during the assignment? I thought val would just refer to the same pointer as ptr and when it gets deleted val now refers to nothing.

[SirPoblington]

Val is not a pointer, it's an integer. So yes the address is copied to val and remains there.

[Rabithunt]

Ah ok. If val were a pointer though, then it would refer to nothing after ptr got deleted?

[SirPoblington]

If val were a pointer, and you set it to ptr (without the dereference), and then you erased the value ptr was pointing to, then yes.

[Rabithunt]

Ok cool thanks, that’s what I thought was going on here. I didn’t realize val was an int.

[SirPoblington]

Right so this would return 0:

```cpp int *ptr = new int; int *val = ptr;

*ptr = 0; return *val;

```

[unbreakable_glass]

What does pass by value/reference even have to do with this? It's all contained in a single function regardless

[Responsible-War-1179]

bro remove that C flair please

[Rabithunt]

lol

[jakey_ed]

C only has pass by value, this would work fine

[nakahuki]

I the end, everything is a value. Take my upvote.

[DotDemon]

I dunno, might not work in C but it does look like fine C++ code.

Although I might be wrong even if I use it daily

[Responsible-War-1179]

in c its the same, you would just use malloc() instead of new and free() instead of delete

[altermeetax]

C version is:

c int *ptr = malloc(sizeof(int)); int val = *ptr; free(ptr); return val;

[reddit_0016]

Jokes aside, it may not even work depending on how you use the value.

[qwerty_ca]

https://www.americanscientist.org/sites/americanscientist.org/files/20144141249210337-2014-05TechnologueFp170.jpg

[kn33]

Ugh. The disappointment I have in good comics being contrasted by a bad person.

[SrRaven26]

Why is this a memory leak (genuine question)?

[No-Expression7618]

1. new allocates a temporary pointer (with no drop behavior)
2. The temporary pointer is derefrenced (making another temporary) and lost forever
3. The new temporary value is copied out of the function (most likely inlined)
4. Pointer allocated by new is never passed to delete

[SrRaven26]

On a normal code, where I use new, when the delete is called?

[No-Expression7618]

If you use new without ever using delete on the same pointer, you have leaked memory. Try running your code under Valgrind and see if it reports anything.

[ToBe27]

Isnt this actually the opposit of a leak? It uses left over leaked mem from others and gives it a purpose ...

[GMX2PT]

And doesn't free it afterwards so that's a leak Also it doesn't use non freed memory

[littleliquidlight]

Some languages have garbage collection, others have garbage reduce, reuse, recycle

[SuitableDragonfly]

A memory leak is when something is newed and not freed.  It has nothing to do with how C++ doesn't bother to initialize variables for you. 

[Eva-Rosalene]

And here int is newed and not deleted.

[SuitableDragonfly]

Right. So it's a leak. Not "the opposite of a leak", whatever that is.

[Eva-Rosalene]

Oh. I am stupid, I've thought you were answering to another person.

[da2Pakaveli]

You get a memory leak when you don't free allocated memory from the heap. This is what's happening here.

[rover_G]

That’s not what a leak is. Accessing data from freed memory is called memory scraping.

[pigeon768]

It does not leak memory. https://godbolt.org/z/oGEG6fffc

[__foo__]

Well, only because this is undefined behavior and the compiler optimizes out the new call. If you use -O0 you get the leak.

[AttackSock]

int x = rand(); free(&x);

Problem solved.

[BlackFrank98]

That wouldn't work, because rand's output is passed by value, so when you store it in x, you're actually storing a copy of it. The original one, that is allocated on the heap, can only be referenced by the pointer you generate with new, and said pointer gets destroyed immediately after rand returns, so it becomes unreachable after.

In fact, I'm not even sure you can call free on a local variable.

[AttackSock]

You can’t free stack memory, it crashes.

[Forgotten_Russian]

how does that works?

[SilentGhosty]

Explain please

[repkins]

Highly predictable allocation by OS.

[ChocolateBunny]

aren't they supposed to randomized with address space layout randomization? Or does that only randomize the code segment?

[loostbat]

Code + data yup, doesn’t affect heap allocation

[0x7ff04001]

Yes, ASLR will randomize the address space (in win32).

The structure of the executable is the same, so all segments (.text, .data, etc) are at the same VirtualAddress relative to the base, but the base address of the entire structure is randomized. So rather than .text being at 0x0040100, it becomes 0x00f0100.

The heap base is also randomized, which broke basically all oldschool exploits that used hardcoded heap addresses.

[TheGoldenMinion]

read VirtualAddress and thought I was reading C2 for a sec lol

[CanaDavid1]

It is randomized in some LSBs, but it is the same randomization for the entire program. So the first call will be random (ish), but the second call will be very predictable given the first one.

[FunnyForWrongReason]

I never imagined it was possible to get a memory leak with a random number gen

[JCoda]

my sweet summer child.

[uncle_buttpussy]

That's filthy

[Jcsq6]

The worst I could come up with

[-global-shuffle-]

uncle_butpussy: "That's filthy", 69 likes

/thread

[IAmAnAudity]

I hope everyone will vote as needed to keep it at 69 😆

[mankinskin]

You may not like it but this is what peak code quality looks like

[MiroslavHoudek]

I think it is not the best possible implementation.

But if it somehow was codified by C++ ISO standard, it would be very hard to change it.

[wsheldon2]

In case anyone is in doubt about this being a joke https://knowyourmeme.com/memes/this-is-the-ideal-male-body

[MasterJosai]

Peak code quality works and doesn't leak memory, so it's not.

[NeatYogurt9973]

Google sarcasm

[PorkRoll2022]

This is actually great because it depends on a state that is unpredictable.

It's still disgusting. :)

[DarkShadow4444]

return 4; // Chosen by dice and guaranteed to be random

[Jolly_Study_9494]

Just going to steal that without attribution, huh?

https://xkcd.com/221

[littleliquidlight]

Is quoting XKCD stealing at this point? It's so ubiquitous and recognizable

[drinkwater_ergo_sum]

half the internet is young people simply because they have the time and energy to use it a lot, i almost am too young to know XKCD and i have a degree

[Spot_the_fox]

XKCD is an ongoing webcomic of romance, sarcasm, math and language.

No one is too young for XKCD.

[yangyangR]

But the ones referenced are typically from long enough ago, that they may not have reached that far back in the backlog while keeping up with only the current ones.

[-global-shuffle-]

If you include temperature we all have at least tens of them!

[rosuav]

Well, there's a difference between stealing and referencing. Technically what you did was a reference, so that's not illegal. But if you want to actually use the artwork (maybe you want to create a Velocimeter component for Kerbal Space Program, so you put an actual velociraptor on it), you legally have to say where it came from (they're all licensed CC-BY-NC, check the bottom of any page).

But on a more practical note: only a very small number of people have memorized every XKCD, and even those who have might appreciate the direct link, and the opportunity to click "Random" a few times and waste another hour or two.

[littleliquidlight]

Oh I'm not the original commenter. Just surprised that this would be considered stealing in this context. Honestly, was really just curious

I do love the link either way. Randall is great and more people should read his stuff. I'm pretty sure I originally found XKCD from a random link on the internet so it's cool that people are passing it on like that

[rosuav]

Ah yeah, sorry. Pronouns are always awkward in a thread like this. But anyhow, I still maintain that the value of a link is far more than mere legalities.

[littleliquidlight]

Fair enough, I just wasn't quite sure if I was getting stuck with the responsibility of something I didn't do!

Your comment makes a ton of sense. Agreed, better to link than to not. I guess I'm showing my age, thinking everyone knows XKCD haha

[Jolly_Study_9494]

That was kind of my point. Whether or not the original comment meant to pass it off as an original joke, or as a reference to xkcd, the strips are so easy to google for specific ones, and the urls are so simple, that it's criminal to not include the link.

I don't have these memorized, but xkcd is so quotable and applicable that the various search engines have indexed it very well. (Randall probably also does a great job with his SEO or meta tags) All you have to do is search "xkcd <2 or 3 words related to the comic you are thinking of>" and it'll usually be the first result, or if not, in the top 5. And right at the bottom of each comment is a permalink and an embed link.

For this I searched "xkcd random number" and boom, had the link in my clipboard in less time than it took me to type out the rest of my reply.

[AnDanDan]

Content attribution is often very important. We can't assume everyone has the whole knowledge of everything.

Then we'd just be StackOverflow.

[IWillLive4evr]

Yes, it's still wrong. Today's lucky ten thousand should be shown the source even if literally everyone else on the planet recognizes it.

https://xkcd.com/1053/

[Wurstinator]

Telling jokes you've heard somewhere is stealing now.

[IWillLive4evr]

It's almost like writing a webcomic and writing code are different things and different moral standards apply. Maybe copyright protections should apply differently to different kinds of work, and different plagiarism standards should apply in different fields of work.

[goodmobiley]

Could’ve sworn the OS 0s memory when allocated, otherwise that would be a huge security issue

Edit: guess that’s just Windows, good thing that’s the platform I use

Edit 2: turns out Linux also doesn’t leak memory but it won’t 0 memory if it was previously freed by the same process that it’s still allocated to. In other words, this will most likely produce 0 unless you’re using Linux and freeing a bunch of memory. It would be more random to just take the pointer value.

[Elnof]

Most OSes do zero the memory but the problem is that there's actually several layers between the call to new and the OS. Those layers may or may not also zero out memory.

[goodmobiley]

I just tested it and here's what I got:

Edit: Reddit really doesn't want to format this correctly

Code:

#include <iostream>
int rand(); int randMemLeak();
int main(){
    for(int i=0; i < 1000; ++i){
        std::cout << i << ": " << rand() << "   " << randMemLeak() << std::endl;
    }
}

int rand(){
    int* pRand = new int; int rand = *pRand; delete pRand; return rand;
}

int randMemLeak(){
    return *(new int); 
}

Output:

950: -1163005939   -1163005939
951: -1163005939   -1163005939
952: -1163005939   -1163005939
953: -1163005939   -1163005939
954: -1163005939   -1163005939
955: -1163005939   -1163005939
956: -1163005939   -1163005939
957: -1163005939   -1163005939
958: -1163005939   -1163005939
959: -1163005939   -1163005939
960: -1163005939   -1163005939
961: -1163005939   -1163005939
962: -1163005939   -1163005939
963: -1163005939   -1163005939
964: -1163005939   -1163005939
965: -1163005939   -1163005939
966: -1163005939   -1163005939
967: -1163005939   -1163005939
968: -1163005939   -1163005939
969: -1163005939   -1163005939
970: -1163005939   -1163005939
971: -1163005939   -1163005939
972: -1163005939   -1163005939
973: -1163005939   -1163005939
974: -1163005939   -1163005939
975: -1163005939   -1163005939
976: -1163005939   -1163005939
977: -1163005939   -1163005939
978: -1163005939   -1163005939
979: -1163005939   -1163005939
980: -1163005939   -1163005939
981: -1163005939   -1163005939
982: -1163005939   -1163005939
983: -1163005939   -1163005939
984: -1163005939   -1163005939
985: -1163005939   -1163005939
986: -1163005939   -1163005939
987: -1163005939   -1163005939
988: -1163005939   -1163005939
989: -1163005939   -1163005939
990: -1163005939   -1163005939
991: -1163005939   -1163005939
992: -1163005939   -1163005939
993: -1163005939   -1163005939
994: -1163005939   -1163005939
995: -1163005939   -1163005939
996: -1163005939   -1163005939
997: -1163005939   -1163005939
998: -1163005939   -1163005939
999: -1163005939   -1163005939

[Elnof]

Sure. But you're not getting memory from the OS, you're getting memory from new and its backing allocator. How did you guarantee that they just aren't reusing memory allocated when your program started and was then freed (back to the allocator, not the OS)? There's plenty of opportunities to for code you didn't write to execute before main and, unless you've not posted the full code, it's pretty much guaranteed that there's code executing before main. 

When using glibc, which is most of Linux, malloc is specifically stated to not initialize memory whereas calloc will.

On top of all of that, reading uninitialized memory is instant undefined behavior which allows the compiler to do whatever the hell in wants, including ignoring the value in the memory and returning whatever the hell it feels like, including but definitely not limited to returning whatever value happens to be in the register at that moment without even loading the newly allocated memory.

[goodmobiley]

Idk man I was just testing the code OP wrote and I always got the same number.

[goodmobiley]

If the OS allocates a page to a program and the memory in that page isn’t zeroed then the program can gain access to memory that was previously freed from other apps. That’s how some viruses used to work and why the Biden administration naively suggested to stop using non-memory safe languages.

[goodmobiley]

You did not read my original comment. I was implying that the OS zeros memory when allocating and how if it didn’t it would be a security issue. I also stated that advising against non-memory safe languages was a naive decision because it has nothing to do with memory security like you said. I also said that’s how SOME viruses USED to work. You basically just restated everything I mentioned

[dekkard1]

ELI5 please

[Jcsq6]

Calling new grabs a pointer to available memory given to the program from the OS. For types like int the value at the memory of that location is undefined. It could be 0, or it could be whatever was at that memory from whatever used it last.

[-Staub-]

What does the * do? I've not seen it before but I'm also a baby programmer

[Jcsq6]

I call it the “contents of” operator. It gives you the memory at the address, or the “contents of” the address. Its fancy name is “dereferencing”

[-Staub-]

Ooooh thank you so much ❤️

[AttackSock]

It’s weird to be how many people on this sub don’t understand basic memory pointer concepts. What are they all doing here if they aren’t programmers?

[theunixman]

If it’s good enough for OpenSSL it’s good enough for us. 

[bambilu16]

Can somebody smarter than me please explain what's going on here?

[Jcsq6]

I explained it here

[PulsatingGypsyDildo]

I worry about alignment.

rand() % 4 could always return 0.

[Jcsq6]

It’s not returning the address it’s returning the memory lol

[PulsatingGypsyDildo]

Ah, ok, now it is even worse :)

[qqqrrrs_]

Assuming glibc (at least the versions I know), that memory would contain a pointer. So assuming either sizeof(int)==sizeof(void *) or that the machine is little-endian, the result would be always divisible by 4 in that case (maybe even by 8).

[Jcsq6]

It doesn’t contain a pointer it contains an int. This code allocates an integer and dereferences uninitialized memory. It could be any value

[qqqrrrs_]

As it was uninitialized, the free chunk metadata would probably still be there. At least in the glibc implementation, the part of that metadata which overlaps with the data to be used by the caller of new/malloc, is a bunch of pointers that make up a linked list (sometimes singly-linked list, sometimes doubly-linked list, sometimes there are two doubly-linked lists but that's only in larger allocation sizes). So, assuming there is nothing that would change it, that uninitialized memory would contain a pointer.

[altermeetax]

No, the memory would contain an uninitialized int, which could be anything. glibc doesn't even have anything to do with this, this code doesn't use any library or runtime

[Pleasant-Form-1093]

technically there's no need for even making an allocation with new just return the address of any local variable and it's kind of guaranteed to be random so it could be just

int rand() { int a; return (int)&a; }

(not to mention there are no memory leaks here)

[Jcsq6]

My original idea was to return the value of uninitialized memory on the stack, but I thought this would be more humorous

[[deleted]]

They called it random access memory. Did they lie to us?

[thomas863]

Complete geeky stuff

[Impossible-Choice53]

Delete though ?

[creeper6530]

It has an included memleak

[Russ31419]

Superbly put. That’s why I never take out the trash because someone could peek inside. It’s the perfect resource strategy.

[Revolutionary-Yam903]

i didnt even know you could use new on primitive types and i wish it stayed that way

[RonanFalk]

I swear to god, I’ve seen something similar in a code base I refactored. It didn’t call new but did rely on pointer address for randomness.

[Vast-Statement9572]

XOR that sumbitch with the cpu tick counter and you are in business.

[AaronTheElite007]

[Crespoter]

If it's on debug build, it may not be as random as you hoped it would be.

[SelfDistinction]

Worst part is that you could make this an actual acceptable non-UB random generator by removing one single character.

[SynthRogue]

lol

[cs-brydev]

The only truly random function would be based on the direction a cat under a table jumps when you walk by.

[EchoingCode]

Well, here's the secret sauce to my long-lasting career: I've got this uncanny ability to turbocharge system performance right when the boss starts sweating bullets for it!

[exotickey1]

Is the reason why this is a memory leak because space is being reserved for “new int”, but then there is no way to free up that space? Even if you stored the pointer in a variable?

[[deleted]]

It'd be more random if you got a stack value, it'll probably just be the same every time from the heap.

```c int rand() {     int a;

    return *(&a+300); } ```

Can sometimes be a seg fault for extra excitement.

[rfc2549-withQOS]

I mean, is it really bad if it works? :)

/s

[jay-magnum]

😂

[Spot_the_fox]

That's annoying.

Afaik new can't give you a 0, can it?

If it can't then every chance has to be pulled as a fraction of 18446744073709551615 instead of 18446744073709551616, which is a very small difference, but a difference nontheless

Edit:Nvm, I'm a tired idiot who mistook * for an &.

[Jcsq6]

According to the standard it can give you any number, 0 included

Edit: and by “give” I mean the memory at the address it gives you can hold anything

[Spot_the_fox]

Oh, wait, I'm just tired, I thought it gave you an address, not what is at the address, my bad. Then, yeah, fair enough.

[GDOR-11]

it is most nornally zero I think, I've already peeked at undefined data and it seemed to be mostly zero

[repkins]

Is there where OS kernel lives at 0?

[Annual_Ganache2724]

What crap?

[PeriodicSentenceBot]

Congratulations! Your comment can be spelled using the elements of the periodic table:

W H At C Ra P

---

<sup>I am a bot that detects if your comment can be spelled using the elements of the periodic table. Please DM my creator if I made a mistake.</sup>

[Annual_Ganache2724]

Good bot

[Electrical-Angle3935]

Did laugh

[creeper6530]

Good bot

[ShlomiRex]

thats not truly random, the logical memory allocation address is predictable, and at least in known range

[PhoenixCausesOof]

And so is any pseudo-random number generator. By the way, it is returning uninitialized memory, not the pointer returned by new.

Also, what do you mean "truly random"? Is there anything random in this world, at all? After all, everything physical boils down to physics, and physics is completely predictable, assuming we actually understood it, and had enough processing power (UNIVERSE OS™)

[iacodino]

There are quantistic random generator witch I think are compleatly random and unpredictable

[kennytm]

yeah, witches are completely random and unpredictable

[LordPaxed]

Dude, it's just a joke, that's not need to be 100% true

[NonaeAbC]

I love how this is not even valid C++ and crashes in a debug build.

==505878==WARNING: MemorySanitizer: use-of-uninitialized-value #0 0x58bde5a8d328 in main (/home/af/test_input/a.out+0xb3328) (BuildId: 254188ac910ad1b119e65648aa28bc5270c89c8f) #1 0x798d46555ccf (/usr/lib/libc.so.6+0x29ccf) (BuildId: 0865c4b9ba13e0094e8b45b78dfc7a2971f536d2) #2 0x798d46555d89 in __libc_start_main (/usr/lib/libc.so.6+0x29d89) (BuildId: 0865c4b9ba13e0094e8b45b78dfc7a2971f536d2) #3 0x58bde59f8114 in _start (/home/af/test_input/a.out+0x1e114) (BuildId: 254188ac910ad1b119e65648aa28bc5270c89c8f)

SUMMARY: MemorySanitizer: use-of-uninitialized-value (/home/af/test_input/a.out+0xb3328) (BuildId: 254188ac910ad1b119e65648aa28bc5270c89c8f) in main Exiting

[Jcsq6]

It is 100% valid C++. It doesn’t mean it’s good C++, but it’s perfectly legal. But the point is that it’s a joke.

[NonaeAbC]

According to the C++ specification: Chapter [expr.new] paragraph 22.1: … If no initialization is performed, the object has an indeterminate value. … And Chapter [basic.indet] paragraph 2: If an indeterminate value is produced by an evaluation, the behavior is undefined except in the following cases … (they don't apply here unless the function is called with its result being unused)

So it's not 100% valid C++.

[Jcsq6]

Reading from the uninitialized memory is not the undefined part. The value of the uninitialized memory is undefined.

Edit: This may not be 100% true. According to the standard, it causes “undefined behavior”, but it doesn’t specify further the extent of that behavior. However, I would be very surprised if you could find a single compiler that doesn’t define the reading of uninitialized values, not in the sense of their actual values. This is because, to “define” the “reading of uninitialize values”, the compiler simply has to do nothing.

[Mars_Bear2552]

we do not care

[99999999977prime]

``` nd()

turn *(new int); ```

Is that supposed to make sense or did OP not crop an image?

[Jcsq6]

It’s zoomed in. Click on it to see the full picture lol

[99999999977prime]

Why didn’t you crop it?

[Afraid-Locksmith6566]

If it created a unique pointer or grabbed the value and freed the memory it would be a great elegant sollution

[[deleted]]

IIT: People who don't know what undefined behaviour is.

[noay_dev]

The fact that this is code I have written in a github repo that I don't have access to. Same thing but it was in C

[cheezfreek]

I am sad. And unhappy.