[SamReidHughes]

What.

What good programs are written in C that don't have well-structured memory management the way C++ does it with RAII?

Edit:

"But in reality, why C is still the best programming language for large projects (IMO) is exactly that the programmer is allowed to choose a suitable structure, such that the program can fulfill the technical requirements. Other languages force the project into a structure that somehow never fits after a couple thousand LOC."

Yeah, this doesn't make any sense. The reason is, C++ doesn't impose anything on your program structure that C doesn't, while C, with the limitations it has, imposes a tax on all sorts of ways of structuring your program.

For example, you can't practically write a program using a futures library (such as the Seastar framework) in C. And every program you write in sensibly written C can be translated to C++. The exception might be really really small-scale embedded stuff that doesn't allocate memory.

[pjc50]

> What good programs are written in C that don't have well-structured memory management the way C++ does it with RAII?

MISRA C standards, popular in embedded projects especially automotive, ban the use of memory management altogether.

The whole point of RAII is that the compiler manages it for you as far as it can. This is impossible in C because you have to do it manually. You might end up writing malloc() at the top and free() at the bottom of functions but that's the opposite of RAII.

[jschwartzi]

Note that they ban the use of dynamic allocation at run-time except via the stack, but that you are still allowed to allocate from the heap as long as that heap allocation is static for the life of the system. This avoids a whole host of problems related to heap exhaustion that result from allocation timing causing heap fragmentation.

[AnimalMuppet]

It also eliminates a whole lot of uncertainty in the timing.

If you're running in an automotive environment, you're probably real time; that is, you have to finish your processing before, for example, the next cylinder comes into firing position. You have to hit that, for every cylinder of every rotation of the engine, for any rotation rate that the engine is capable of reaching. You can't be late even once.

Now in the processing you have a malloc call. How long will the call take? Depends on the state of the heap. And what is that state? Depends on the exact sequence of other calls to the heap since boot time. That's really hard to analyze.

Yes, you can get a memory allocator that has a bounded-worst-case response time, but you also need one that absolutely guaranteed always returns you a valid block. And the same on calls to free: there must be a guaranteed hard upper bound on how long it takes, and it must always leave the heap in a state where future allocations are guaranteed to work and guaranteed to have bounded time.

And, after all of that, you still have a bunch of embedded engineers scratching their heads, and asking "explain to me again how allocating memory at all is making my life easier?"

So embedded systems that care about meeting their timings often allocate the buffers they need at startup, and never after startup. Instead, the just re-use their buffers.

[jstimpfle]

RAII is a disaster. Piecemeal allocation and wild jumping across the project to do all these little steps (to the point where the programmer cannot predict anymore what will happen) is not the way to go.

Then all the implications like exceptions and needing to implement copy constructors, move constructors, etc. in each little structure.

As to what C project doesn't just emulate RAII: Take any large C project and you will likely find diverse memory management strategies other than the object-oriented, scope-based one. Also, other interfacing strategies than the "each little thing carries their own vtable" approach. The linux kernel is one obvious example, of course.

But I also want to reference my own current project since it's probably written in a slightly unusual style (almost no pointers except a few global arrays. Very relational approach). https://github.com/jstimpfle/language. Show me a compiler written in RAII style C++ that can compile millions of lines of code per second and we can meet for a beer.

> The reason is, C++ doesn't impose anything on your program structure that C doesn't

Of course you can write C in C++ (minus designated initializers and maybe a few other little things). What point does this prove, though?

[SamReidHughes]

I guess you're the yin to my yang, because I've got a compiler written in C that doesn't use any global variables at all: https://github.com/srh/kit/tree/master/phase1

It wasn't really implemented for performance, and maybe the language is more complicated -- no doubt it's a lot slower. On the other hand, I can look at any function and see what its inputs and outputs are.

[jstimpfle]

My compiler isn't optimized for performance, either! I didn't do much other than expanding a linear symbol search into a few more lines doing binary symbol search. And I've got string interning (hashing).

I've mostly optimized for clean "mathematical" data structures - basically a bunch of global arrays. This approach is grounded on the realization that arrays are just materialized functions, and in fact they are often the better, clearer, and more maintainable functions. If you can represent the domain as consecutive integer values, of course. So I've designed my datastructures around that. It's great for modularity as well, since you can use multiple parallel arrays to associate diverse types of data.

But anyway, your language looks impressive I must say.

[aswanson]

What are your thoughts on D or Rust as they compare to C++?

[SamReidHughes]

Rust makes intuitive sense to anybody that knows C++ and Haskell (deeply enough to have seen the ST type constructor). There are some natural, healthy memory management decisions you might make in C++ that you can't do in Rust, but that's life. The obvious example would be if you want one struct member to point into another. I like Rust traits or Go style interfaces over classes. cppreference is far far better than any Rust documentation, which aside from Rust by Example, is an unnavigable mess. Oh, and it would be nice if C++ had discriminated unions.

I don't know enough about D to really comment on it (I read the black book on it 9 years ago, and the examples crashed the compiler), but... it has better compile times, right? There's a module system? I'd have to look at the D-with-no-GC story, figure out how hard it is to interop with C++ API's. I think I'd have better feelings about D (or C++) if it didn't have class-based OOP.