You (probably) don't need to learn C
nedbatchelder.com
nedbatchelder.com
The problem with those takes is that it always come from the people that already know it and had a lot of baggage that distorts it’s view that no one else should learn.
Due to several reasons I always worked with high level languages and last year I started to learn C and C++ and how beautiful was to know exactly how are you allocating resources in your application that I felt quite good programming mentally and intellectually.
When you come from a world of resource overprovisioning (CPU, memory) when you start to get your head about those languages that puts performance first, you feel good about it in the first moment but in the second after you feel that your whole experience was subpar due to lack of a thought process.
Of course, as the author implies there's an MMU, register renaming, not to mention a whole OS involved, so how "exactly" are we talking about? As Blake wrote, there's "a world in a grain of sand".
(Of course I'm excited for you and share your pleasure in understanding memory layout and its implications. Computing is really fun the less abstract it is. And that sheer depth means we can plumb those depths -- or heights -- as far as we like).
Along the time I was not exposed to those "low level" languages and it had the effect that I never had that perception. That's why I felt that my experience was subpar: In a point in time, I was living in a complete different epistemic universe even being on the technology.
In this case, Programming in C. Will it make you an expert C programmer? No. But it will absolutely increase your knowledge on how a modern computer works.
Haha. It's true of webdev now, but I irrationally rejected that advice as hard as I could. Made job search more difficult. But, ever since I learned C, I felt that, if I can't "low level" program, I'd rather not program at all. >:]
Inb4 C is a high level programming language.
And it paid off: I now work with like-minded nerds and tech I'm passionate about. (As opposed to anything web-related, which gives me some kind of ineffable dysphoria for a multitude of reasons, some scrutable and some not.)
There is definitely a whole bunch of lower layers, but you cannot really get to them, so I think it's pretty fair to call C "a lowest layer language for userspace after assembly". And probably for kernel programming, too - C gets into implementation-defined behavior when there are MMUs involved, but that's not a big practical problem.
(if you work at Intel and have access to secret microcode definitions than C is not a high level language... but cases like this are super rare)
It's also a fine beginner language, especially in a structured university setting imo.
Yes, you probably don't need to learn it. But it can come in handy. For instance, there's a wealth of useful software out there in C. It's nice to be able to read its source, hack on it, or leverage it from your higher-level language via FFI.
Writing simple programs was fine enough, but the whole matter of linking libraries and writing Make files was a headache.
Build and testing tooling is one thing that younger languages have generally done much better. Rust, Go, Dart and others all have standard build tools integrated with the language that scale to large projects, with standard testing frameworks integrated with those tools. Scripting languages like Python have import features within the language itself. Much lower cognitive overhead.
But if you (1) choose a single OS, (2) have "few" (say under 20) files and (3) rely only on OS-provided libraries, then things are actually pretty simple. For example, you only support Ubuntu 20.04 or Fedora 39. Then your makefiles are nice and easy to read, and you just rely on pkg-config for the libraries.
This is partially why C is a common teaching language. Because you have to build a lot of tools that are easy to take for granted in other languages. Take a Map or Dictionary for example. C doesn't technically speaking provide one, so you learn to implement them pretty quickly and often. Technically speaking C doesn't even have a primative string type, you just create an array of chars, which by the way has to be a pointer. While this is super easy to do once you've seen it once or twice, it teaches you how strings work in almost every other language.
The reason you can trivially loop through a string in python, is because it works the same way, they have just abstracted it a tiny bit from you.
Now to the author's point... does that really make you a better developer to know that? Therefore is it really needed? No probably not needed. But these exercises and experience does help solidify more complex topics later on. So you don't need C, but I still think there's benefit in learning it.
I take issue with the "quickly and often" part, but you do learn to implement them! And that provides valuable insight when it comes to other languages.
I've had senior devs who, like past me, didn't understand why removing an element from a vector or map invalidates iterators or indices on it. I learned precisely why when implementing vectors in C: the usual implementation of those collections shifts everything around to maintain element contiguity in memory, so now your iterator/index is pointing to a different element (which incrementation will skip) or possibly past all the elements!
And when you're presented with these fancy data structures in Java or Python, that feels unintuitive and wrong. "Come on; I should be able to just iterate through this and remove certain elements as I go," like you would remove objects from a shelf. The shelf doesn't rearrange the objects after you take one out! But the reason it feels like an affront to common sense is that you've been trained to take the fancy data collections for granted and not forced to understand the complexity behind them that makes them efficient.
Of course, the real answer is to do that with some functional algorithms, like `std::remove_if()`, instead of via iteration. That way, you'll really be in the cloud-scraping ivory tower and never have to think about what's going on below. https://youtu.be/ggijVDI6h_0 :p
They are complex if you are coming from the Python world. To truly know their recursive declaration syntax, you have to see it from a compiler's perspective. Pointer arithmetic isn't something you do often even in C++. It's a crude kind of reference that can be mutated arithmetically and doesn't provide any safety whatsoever. It maps well to the indirection mechanisms and addressing modes provided by the underlying hardware.
Don't mistake the complexity with ease of making mistakes though.
This might just be because C++ broke my brain into assuming:
Object foo = other_object;
It really helps if you understand assembler addressing modes. Then it makes total sense.
(Unless you are talking about x86 real mode segment registers. Luckily, we can leave this behind and never talk about them again :) )
Man, what a bold claim. I could say all kinds of things about the number of books written about C, the size and complexity of its compilers, the failure of even veterans to avoid mistakes, the constant disagreement amongst even experts about the most fundamental things like realloc, but my only argument--indeed the only argument I need--is that the standard [0] is literally hundreds of pages.
> pointers aren't complex
Pointers are so complex they're responsible for the vast majority of security bugs across all of computing history, and they're so powerful and overloaded that they can't be fixed without bonkers hardware interventions like CHERI. You might say, "nah it's buffers" but when you have a pointer, everything is a buffer! You might further say "nah it's random undefined behavior", but it's very, very hard to use a pointer without invoking undefined behavior. Here's a quick thing I googled:
int func(int **a)
{
*a = NULL;
return 1234;
}
int main()
{
int x = 0, *ptr = &x;
*ptr = func(&ptr); // <-???
printf("%d\n", x); // print '1234'
printf("%p\n", ptr); // print 'nil'
return 0;
}
Look I love C, but it's deeply complex and a lot of that is pointers.
[0]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3054.pdf
But all of those problems that C++, Rust or Zig solve - these all are discussed in terms of C. Toolchains, OSes, concepts of static and dynamic linkage are all defined in terms of whatever few abstractions C provides.
And sometimes all you have is a good old C compiler. Because C is everywhere.
It is not necessary to know the language but it sure is useful to see beneath and beyond.
C is a high level language that maps very straightforwardly to what the hardware does and programming on a microcontroller without an OS let's you eliminate a ton of abstractions that otherwise take years to comprehend.
If someone wants to understand what's going on "behind the scenes" then it's going to be very useful for the to know C before trying to learn how the Cpython interpretor or JVM work.
If you want to understand "how a computer works" - well sure C has gone from low-level to a high-level language. But the model of "how a computer works" - from Python or Ruby or JavaScript - that's very often expressed in C: kernels and libraries, in multiple layers. There's so much rich information in C code bases on why something behaves like it does. Whole histories of computing are expressed in C - types and APIs that tell you why something might work on one computer and not on another.
So sure, don't learn C if you don't need to, but it's not hard to understand if you're motivated. And it really does expose you to how a computer works in ways you won't find in higher-level languages.
Lots of people certainly can survive without knowing any C, I'm just saying that it is not an irrelevant thing and if you have the time to invest in learning a bit more than the basics, it is not a waste of time.
I think we're just violently agreeing. You posted a few reasons people may feel compelled to use as reasons to learn C that are misleading. I'm just adding to that from my personal experience that learning C, even if you are not going to use it every day, also has a collateral advantage to help when talking to people who "think in C" as an abstraction.
Peace.
The semantics of C really fit how what I think about what computers do: that we move around things between boxes of memory and between registers. That computers is largely logistics between "places". Edit: It's a bit like a factory as in factorio
I didn't write it in Rust because I find the semantics of C++, Rust, Haskell and other functional languages to be much more abstract and harder than this simple idea of stateful movement.
The nand2tetris course is a pretty good one; you'll design the hardware itself in the first part and in the second you'll build a compiler/VM/etc for it.
And then you'll gain an appreciation for how C works and why it's useful.
And also why higher-level languages are useful.
I don't think you need to learn C any more than you need to learn separation logic or category theory though.
Update The problem with "learning C" is that it has a ton of warts and you might injure yourself in the effort to master it. The language is coupled tightly to libc, the specification is small as far as modern ISO standards go but it still leaves a lot to the imagination (and the implementors). It's really quite a complex language to learn well due to all of the sharp edges.
And of course, C isn't the royal road. There are lots of other models for thinking about programs that aren't based on imperative procedures. It's just a language.
If you want to think about programming and PLT... there are a lot more sophisticated tools.
"you should learn a systems language, if you want to be a 'complete'/'well-rounded' SWE"
C was never the point (it was just the common low level language), the point was that just learning PHP/Python/JavaScript/Ruby wasn't enough to get a full grasp of everything that's going on, since they hide a lot of the warts from you.
I, personally, still believe this. That being said, you can definitely make a career out of doing nothing but JavaScript/TypeScript/React, PHP/Laravel, RoR, etc.
So we aim for well-rounded. That's the best we can maintain.
Careful: In C, memory isn't a huge array of bytes.
In other words, location 0x0000ffff in your application does not map to system location 0x0000ffff, but instead a translated portion of said block. In addition, there are no guarantees as to how that memory will be ordered/allocated/segmented outside of specific requests for a contiguous block of memory via something like malloc. You can assume your array (static and dynamic) is contiguous, but that's the only assumption you can make.
If you were to write freestanding C code, this certainly changes. At which point the memory model becomes "what you decide to provide".
That doesn't make sense; the OS itself is written in C.
> If you were to write freestanding C code, this certainly changes. At which point the memory model becomes "what you decide to provide".
Okay, so we're back to, C doesn't impose anything on you, though the OS may.
Please point to a non-userspace memory allocation library/implementation that does not rely on lower level logic to function.
> Okay, so we're back to, C doesn't impose anything on you, though the OS may.
You're just reversing the original statement.
The statement was "you can't assume anything about memory in C" (paraphrasing). They then asked "why not?"
The explanation is that:
What you think is 'memory' in C isn't, and certainly doesn't map to what most people assume about memory; because C doesn't impose a memory model, it relies on the underlying OS/environment to do so. The only "memory model" is thus: a requested allocation (whether on the stack or heap), if provided to you, will match your request; all other assumptions are invalid.
If you want to move goalposts, argue about logical boundaries, etc, have at it. Or if that answer doesn't satisfy you, I don't know what to tell you; but simply rephrasing the original problem does even less.
[0] https://wiki.osdev.org/Global_Descriptor_Table
[1] https://wiki.osdev.org/GDT_Tutorial#Telling_the_CPU_Where_th...
> In addition, there are no guarantees as to how that memory will be ordered/allocated/segmented outside of specific requests for a contiguous block of memory via something like malloc. You can assume your array (static and dynamic) is contiguous...
The standard can only be referring to the abstract machine. In truth, your OS might give you 1,000,000 elements on 1 page, and 1,000,000 elements on a different page, which exist nowhere near each other in RAM (or have been swapped to disk, etc. etc.), or are being CoW'd into existence, and so on.
This is empirically true--from the days when programs like Chromium would try and malloc all the memory in a machine. The pointer that malloc returned could not have referred to a contiguous memory block. You can try it on your machine by malloc'ing more memory than you have and then reading from the blob.
[0]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3054.pdf#s...
This is where the "model" portion of the statement comes into play and why OPs point is even more cogent. The memory will be virtually contiguous, even if it's physically disparate.
I don't really understand the value of extolling the fact that like, you can incrementally iterate through an array in C. The days of systems with segmented memory are long behind us, and even then it wasn't like you'd have an array that spanned segments--you couldn't! Honestly what language/platform exists that doesn't have this property and what would that even look like? Like you'd somehow have to know that elements 100-200 in an array are "no good" and you have to skip them?
People keep trying to put meat on the very basic bones you've got here, but you keep insisting that, yep, 2 comes after 1 and 717 comes after 716. Great! We know! And we say stuff about how trying to index off the end of an array leads to UB, or how the array may not actually be contiguous in physical memory, or it might be in various caches, or how sometimes your array goes from 1024 members to 1025 members and your FPS drops from 300 to 30 because you fell out of cache, and you're like, "sure but you still access arrays with consecutive indexes". Well, yeah! It's kind of the point of using C that you have access to or some control over these kinds of things. They're useful to the conversation. Continually bringing us back to indexing... I don't think is.
> This is where the "model" portion of the statement comes into play and why OPs point is even more cogent.
Eh, "memory model" is a specific phrase referring to how memory is defined to work in a threaded environment [0]. The original "Help us understand: what is the model of memory in C?" prompt is referring to the fact that unless you prolifically use the API in stdatomic.h (which very few things do), you just have undefined behavior all over the place if you ever dare to use anything related to threads. Also, it was only defined in C11--not a lot of things have updated, even now.
---
Overall I want to emphasize that this whole thread is doing a real good job of proving Ned Batchelder's point: even people who think they know or understand C don't (to be clear, I do not think I understand C), and things are generally alright. There's--clearly, reading through everything--a culture of "You need to be an expert in some low-level, 'real' language/platform before you can write meaningful software", but you don't, and my evidence is Facebook, maybe the most influential software ever written.
But I think the OP’s point is more about how when you allocate memory, you get an array of bytes to play with. And all higher level languages build on top of that and abstract it away as much as they can.
Will I get arrested? No.
Will the compiler stop me? Also no.
Will the program crash? Maybe. Almost certainly if I do it often, or without understanding.
You aren't guaranteed to be safe if you access memory or addresses outside of allocations you've made (with stack and static memory counting as "allocations you've made).
But on embedded systems with memory-mapped I/O, I have done things like
*(unsigned long *)0xFFFE1404 = 0x00011472;
But of course an implementation is free to define additional behaviors beyond the C specification. That’s done all the time. But that’s really a “flavor” of C and not pure “vanilla” C.
An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.
Any pointer type may be converted to an integer type. Except as previously specified, the result is implementation-defined. If the result cannot be represented in the integer type, the behavior is undefined. The result need not be in the range of values of any integer type.
Also, the C standard merely codified existing practices and common extensions. Actual use of C has converted integers to pointers for a long time. If converting integer literals into pointers were undefined behavior, it would just show that the C standard isn't being practically useful in one area (since it's commonly done in practice).
Quite probably since the first C-based implementation of Unix on a PDP-11. So it's been known to be "a thing that C does" for quite a bit longer than the standard existed.
Say I'm doing my original example, working on an embedded system. My code isn't going to port to anything that doesn't have the same hardware, so architecture isn't an issue. Any compiler supporting that architecture for an embedded application is going to do the right thing with that kind of C statement, so that isn't an issue either.
So, implementation-defined means that you can't count on compilers doing the same thing. But there are some things that are implementation-defined where you can pretty much count on any compiler doing the same thing. And, as trealira said, compilers are supposed to clearly state what they do in such cases, so you can read the compiler's statement and see if there are any surprises.
This is less true if you're writing library code. There, you have to support all compilers, or at least all conforming ones, and you have to make fewer assumptions.
https://en.wikipedia.org/wiki/Far_pointer
https://en.wikipedia.org/wiki/X86_memory_models
However, this is not standard C.
If you want something constructive, what was the point of the post if you're wrapping it up with "learning C can be useful"? I love C, it's fantastic and it has taught me a lot about how and why some things are as they are. Just compiling with a simple lib helped me understand headers and the -devel packages some distros provide. The difficulties doing so efficiently shows why newer languages have package managers. Another point could be that the entire world runs on C, and knowing it can help either porting software safely or maintaining projects.
Basically what I get from it is: "you (probably) don't need a drivers license, unless you want to drive, then get one". Sometimes the journey can be extremely beneficial even if there's no direct use. Would you claim learning C hindered you in any way?
The point of the post is that abstractions are inevitable and you choose your own level. And: you can be a great programmer without knowing C.
Absolutely, but I get the feeling you're taking the common statement "learning C can be a great experience" and bastardazing it into a straw-man "you NEED to learn C" that you then argue against.
I just think it's an obvious statement and it reads like you're being nagged by people to learn, but you don't want to learn C and defend your position. For me nothing has taught me so much about development than a weekend hacking in C and stepping through the code with Valgrind or reading the binary output did. And I recommend all my peers do the same, most don't and that's okay. But I think it's a shame that people in general don't seem to care that much outside of work.
I did enjoy the read though, even if clickbaity.
Why C as opposed to other languages? It's portable and very simple on the surface, there's not much to it but difficult enough to be a teachable opportunity.
The physical memory isn't necessarily contiguous, but the model of memory is. Which is the entire point. arr[0] and arr[999] are 1000 virtually contiguous blocks.
You can confirm that in the spec here: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
> it'll also give you something random should you go out of bounds.
Out-of-bounds array accesses are UB
> it'll also give you something random should you go out of bounds.
Are you just taking umbrage with the word I used? "random" clearly is meant to imply that the language makes no guarantees.
Uninitialized memory/data isn't "random", it's specifically null. Random could be something uninitialized, or it could be the kernel entrypoint or it could be a pixel data byte from some BMP.
Ooh that's very untrue [0].
Although, I guess I should make sure we're talking about the same thing. I'm saying this is undefined (the little program I've linked below):
#include <stdio.h>
int main() {
int a[4] = {0, 1, 2, 3};
int b = a[1000]; /* undefined behavior! */
printf("%d\n", b);
}
Suffice to say, my original statement clearly matches what you seem to be getting at; whether you like the choice of words or not.
But, maybe I've been too much of a jerk here! Maybe I jumped too hard into "someone's wrong on the internet!" mode. It's OK to be wrong, cool and rock and roll even. Lord knows I've been wrong and will be wrong again. If this is true then I've embarrassed myself and I apologize. Let's go forward and be excellent to each other.
But C lets you treat memory like a huge array of bytes. You can do things like:
char *p = (char*)0;
char value = p[address];
Of course it is; the platform you are used to might have additional constraints, but that is outside of C itself.
On your platform (hardware/OS combination) it may not not be an array of bytes, but rest assured that conforming C compilers exist on platforms, such as embedded ones, where you can literally get a pointer to address zero, and use all the RAM as a huge array of bytes.
Long ago, a friend of mine - a brilliant developer, who nevertheless never dug any lower than basic C++, once tried to write a simple C program that printed out some text. His first attempt went something like:
void greet(char *name) {
char *text = "Hello, ";
text += name;
text += "\n";
printf(text);
}
Being able to follow along in the PostgreSQL source code has been helpful when we see production behavior we don't expect.
The article points out that:
`C is far removed from modern computer architectures: there have been 50 years of innovation since it was created in the 1970’s.`
Is there a C-like language that uses abstractions based on current ARM or x86 processors? i.e. something above assembly that learning would help us understand how these modern processors actually work?
You can write fast software today in assembly, C, C++, Rust, and languages like that. You don't need to go to the microcode level. The reason we have trouble with slow, bloated software today is because people don't do that, and instead use slower languages, like Python or JavaScript, using inefficient algorithms, with lots of potentially unnecessary dependencies that optimize for the general case, and not whatever specific problem the programmer wants to solve (which is often less efficient as well).
For me, awk, PHP and JavaScript come to mind, but the list is rather long:
https://en.wikipedia.org/wiki/List_of_C-family_programming_l...
The 40 pages of Chapter 2 in The AWK Programming Language (first edition) is a superb introduction to the syntax and control structures in this family.
https://archive.org/download/pdfy-MgN0H1joIoDVoIC7/The_AWK_P...
Other reasons to use C are speed, control, and systems programming.
Why not just learn the language that you want to learn?
Reading the AWK book is like skipping ahead on a few subjects.
[1] - https://www.amazon.com/Computer-Systems-Programmers-Perspect...
Are there languages where these are visible? Any time I've seen them discussed it's been in terms of writing C/C++/Java that understand how they work, e.g., the disruptor pattern padding variables to a 64-byte cache line.
> C teaches you an abstraction of computers based on the PDP-11.
Hmm, I'd wonder how a C designed today would look based on modern architectures.
https://medium.com/@devyjoneslocker/understanding-pythons-pa...
It's also not a bad idea to learn the correct way to open and read a file into memory using C (a page of code at least, with lots of NULL checks and malloc and free), just to appreciate how much work something like Python (a few lines of code) is doing for you under the hood.
But if you want to get a feel for what the hardware might be doing, as the author says, C is not a good choice, and never really was. If you want to start to understand the hardware, write some assembly code. It's not that hard, but you have to think about the actual hardware model.
The author's other point is also correct (much as it irks me -- I want to know everything): nobody understands the whole vertical stack from quantum mechanics to the latest frameworks, much less its horizontal ramifications (subtleties of TCP implementation or category theory). I could creditably* describe perhaps 60% of how a car works these days but I can no longer do more than simple maintenance. Infuriating, yet surely a good thing.
* creditable, sure, but credibly? Not for me to decide.
I use Python for glue code and for running unit tests and other boring stuff and find it frustrating with too many ways of doing things, too many libraries for achieving the same thing.
It could be I am still bitter because Python3 broke a bunch of my scripts by forcing everything to be a byte array.
PS You dont need to attend school or university. But I bet nearly every parent tells their kids to attend and graduate with good grades.