Important reminder just in the Preface :-)
Takeaway #1: "C and C++ are different: don’t mix them, and don’t mix them up"
replies(8):
This is how I managed to sneak C++ into an embedded C codebase. We even created some templates for data structures that supported static allocation at compile time.
Sooo... yeah... I should definitely change company!
https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-an...
I guess what you're really asking is what are the best or most common ways to do OO in C?
Another big one that I always forget C still doesn't support is function overloading.
Where can I find something about objects being "think of your code as representing the state and interactions of objects" honesty totally new to me.
So no, certainly I'm not asking ways to do OO in C. But it seems to be more definitions of object orientation as I thought...
Yes you can do it less cleanly with macros or inline functions. But you can't do it performantly with struct and function pointers.
C++ imo doesn't offer anything compelling for the embedded usecase. Especially not considering all the footguns and politics it brings.
You can of course be strict and diligent about it but if you are you are pretty much just writing C anyway. Better to do it explicitly.
Allowing the use of the C++ standard library has been one of my biggest regrets (not that it was my decision to make, I fought it).
But why would you do that if you have an instrument that lets you work at the same level as C, but with methods provided as a proper abstraction that maps exactly to what you'd have written yourself anyway?
If you do that, you'll notice that, for example, encapsulation is not a part of that de facto definition, because languages like Python and (until recently) JavaScript lack it, despite being considered OO.
Indeed, the only two things that appear to be consistently present in all OO languages are: 1) some notion of object identity as distinct from object state, and 2) runtime polymorphic dispatch.
But I write ; i++){ and seeing it the other way round throws me off for a minute, because I think, as you put it, why would you use those very particular semantics?
But I guess this is only a semantic argument.
This is not one of those beginner -> journeyman -> expert cycles where coincidentally the way you wrote it as a beginner is identical to how an expert writes it but for a very different reason. I'd expect experts are very comfortable writing either { x = k; k += 1; } or { k += 1; x = k; } depending on which they meant and don't feel an itch to re-write these as { x = k++; } and { x = ++k; } respectively.
I'm slightly surprised none of the joke languages add equally frivolous operators. a%% to set a to the remainder after dividing a by 10, or b** to set b as two to the power b or some other silliness.
If you're asking why people use pre-increment by default instead of post-increment, it's mostly historical. The early C compilers on resource-constrained platforms such as early DOS were not good at optimization; on those, pre-increment would be reliably translated to a simple ADD or INC, whereas code for post-increment might generate an extra copy even if it wasn't actually used.
For C++ this was even worse with iterators, because now it depended on the compiler's ability to inline its implementation of postfix ++, and then prove that all the copies produced by that implementation have no side effects to optimize it to the same degree as prefix ++ could. Depending on the type of the underlying value, this may not even be possible in general.
The other reason is that all other unary operators in C are prefix rather than postfix, and mixing unary prefix with unary postfix in a single expression produces code that is easy to misunderstand. E.g. *p++ is *(p++), not (*p)++, even though the latter feels more natural, reading it left-to-right as usual. OTOH *++p vs ++*p is unambiguous.
> it is hard to say no to you, and I’m sorry to say it. But we have to choose a focus, and our focus is to implement (the standard) and innovate (with extensions like everyone but which we also contribute for potential standardization) in C++.
I mean, yeah if it came from a two member team at a startup, sure focus on C++, understandably. But Microsoft, what happened to "Developers! Developers! Developers!"?
I’m scratching my head how you think this is materially different than what you described in your first para. s/state/data and s/interactions/methods.
If anything though I would say the GP is more aligned with the classic definition as it highlights the focus is more on the messages (interactions) themselves rather than the implementation.
Where "mixing C/C++" is helpful:
- I "mix C in with my C++" projects because "sqlite3.c" and ffmpeg source code is written C. C++ was designed to interoperate with C code. C++ code can seamlessly add #include "sqlite3.h" unchanged.
- For my own code, I take advantage of "C++ being _mostly_ a superset of C" such as using old-style C printf in C++ instead of newer C++ cout.
Where the "C is a totally different language from C++" perspective is helpful:
- knowing that compilers can compile code in "C" or "C++" mode which has ramifications for name mangling which leads to "LINK unresolved symbol" errors.
- knowing that C99 C23 has many exceptions to "C++ is a superset of C" : https://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B...
The difference is that i++ has to keep a copy to the original around as the return value is the pre-increment value, while with ++i that isn't needed as the resulting value is being returned.
In the for loop that shouldn't matter as a) for an integer it is essentially for free (it is just reordering when the relevant register is set) and b) that value is hopefully optimized out anyways by the compiler, however as there are cases where it matters some people prefer the ++i style, some just think it looks better.
The C library headers for libraries I write often include C11/C99 stuff that is invalid in C++.
Even when they are in C89, they are often incorrect to include without the include being in an `extern "C"`.
The modern fmt-inspired std::print and std::println etc. are much nicer, preserving all the type checking but losing terrible ideas like stored format state, and localisation by default. The biggest problem is that today C++ doesn't have a way to implement this for your own types easily, Barry illustrates a comfortable way this could work in C++ 26 via reflection which on that issue closes the gap with Rust's #[derive(Debug)].
There's an effort to extract the good parts and make it work for embedded use cases or even bring them into C. Khalil Estelle on WG21 has been working on an experimental, deterministic runtime for exception handling, to give one example. Constexpr is an example of the latter that's now showing up in C23.
It takes a little bit of an effort to make a header work on C and C++. A lot less effort than making a single Python file work with Python 2 and 3.
One of the most compelling things C++ offers to embedded use case is moving runtime initialization to compile-time initialization by liberally using constexpr functions. You literally ask the compiler to do work that would otherwise be done at runtime.
Almost seamlessly. You have to do
extern “C” {
#include "sqlite3.h"
}
for(auto it = begin(v); it != end(v); ++it)
Indeed, and yet here we are with C23
> The change of heart was the new management, and the whole Microsoft <3 FOSS.
Yeah, agree. To me the turning point was when they created WSL.
But without exceptions it is mostly syntactic sugar anyway.
If compile time initialization is the most compelling usecase I'll rest my case. Good feature, yes! Hardly worth switching language for.
cin >> a;
Then the program goes berserk as soon as the first non-number is read out of standard input. All the other "cin >> integer" lines are immediately skipped.
Yes, I know about error checking, clearing error condition, discarding characters. But it's a whole lot of stuff you need to do after every single "cin>>" line. It makes the simplicity of cin not worth it.
It's telling that every compiler toolchain that compiles C++ also compiles C (for some definition of "C"). With compiler flags, GCC extensions, and libraries that are kinda-sorta compatible with both languages, there's no being strict about it.
_My_ code might be strict about it, but what about tinyusb? Eventually you'll have to work with a library that chokes on `--pedantic`, because much (most?) code is not written to a strict C or C++ standard, but is "C/C++" and various extensions.
I’m not sure about the stdlib version, but with fmtlib you can easily implement formatters for your own types. https://fmt.dev/11.0/api/#formatting-user-defined-types
You check error for the whole batch.
* Performance
* Support for localization (as the format string and positions of values to format differ between languages).
* Code reuse & dogfooding - the data structures used in iostreams are not used elsewhere, and vice-versa
* C and OS interoperability - as you can't wrap a stream around a FILE* / file descritor
* bunch of other stuff...
iostreams work, but are rather crappy.
The less C the merrier.
If you care about correct use of localisation, standard C and C++ libraries aren't really what you're looking for, or even C and C++ to start with.
Hindsight is 20/20, remember that. Streams are not that bad of an idea and have been working fine for decades. You haven't named a problem with it other than the fact the operators are used for other stuff in other contexts. But operator overloading is a feature of C++ so most operators, even the comma operator, can be something other than what you expect.
>The biggest problem is that today C++ doesn't have a way to implement this for your own types easily, Barry illustrates a comfortable way this could work in C++ 26 via reflection which on that issue closes the gap with Rust's #[derive(Debug)].
You can trivially implement input and output for your own types with streams.
You appear to be a Rust guy whose motive is to throw shade on C++ for things that are utterly banal and subjective issues.
The only reason why iostreams are slow is because of its incompatible buffering scheme, and the fact that C and C++ need to stay in sync when linked together. And that brand of slow is still faster than other languages, except sometimes those that delegate i/o to pure C implementations.
But having the "class" keyword is nice. Having built in support for member functions is nice.
Sometimes a person just wants the simplicity of C++ 2003.
(In reality I was working on a project where our compiler only supported C++ 2003 and we had a UI library written in C++ 2003 and honestly pure C UI libraries kind of suck compared to just sprinkling in a bit of C++ sugar.)
I agree. It's lunacy. just be explicit and use functions or equivalent like literally every other language.
void remove_char(char *s, char c) {
size_t i, j;
for (i = j = 0; s[i] != '\0'; i++)
if (s[i] != c)
s[j++] = c;
s[j] = '\0';
}
There are also idioms for stack manipulation using them: "stack[sp++] = pushed" and "popped = stack[--sp]".
C code does a lot of incrementing and decrementing by one, and so having dedicated syntax for it is convenient.
> If you care about correct use of localisation, standard C and C++ libraries aren't really what you're looking for, or even C and C++ to start with.
> You can do anything in C that you want to.
fscanf (STDIN, "%d", &a);
in both cases, you need error checking (which you "know about").
struct Foo {
int a;
float b;
std::string c;
};
Foo foo;
std::cout << foo;
I believe Rust has adopted similar idioms. I’ve heard the overall idea referred to as Railway-oriented programming.
In C++ you could implement it with exceptions, though they bring in a bunch of their own baggage that you don’t have to deal with when using monads.
while(*d++ = *s++)
;
loop: move.b (a0)+,d0
move.b d0,(a1)+
bne loop
loop: mov al,[rsi]
mov [rdi],al
inc rsi ; extra instruction!
inc rdi ; extra instruction!
cmp al,0
jne loop
This disn't stop with <iostream>, they keep doing it - the latest example I can think of is std::ranges operations being "piped" with |.
1. prefix incr/decr precedence: "stack[--sp]"
2. postfix incr/decr precedence: "s[j++]"
3. i have no particular preference for the precedence and am just using a shorthand I inherited from my ancestors whose use cases are no longer relevant to me: "i++" in your for loop
My rank speculation is that C programmers get in a habit of #3 and then forget to consider precedence in an expression where it matters.
In any case, it would be interesting to do a scan of github to see how often prefix and suffix incr/decr had to get switched up in a bugfix patch.
Absolutely true. I generally insist on folks learning C and C++ interoperability before diving in to all the "Modern C or C++" goodness. It helps them in understanding what actually is going on "under the hood" and makes them a better programmer/debugger.
See also the book Advanced C and C++ Compiling by Milan Stevanovic.
Many C++ coders are oblivious to those differences (myself included before I switched from 'mainly C++' to 'mainly C') because they think that the C subset of C++ is compatible with 'proper' C, but any C code that compiles both in a C++ and C compiler is actually also a (heavily outdated) subset of the C language (so for a C coder it takes extra effort to write C++ compatible C code, and it's not great because it's a throwback to the mid-90s, C++ compatible C is potentially less safe and harder to maintain).
For instance in C++ it's illegal to take the address of an 'adhoc-constructed' function argument, like:
sum(&(bla_t){ .a = 1, .b = 2, .c = 3, .d = 4 });
Interestingly, Objective-C leaves its C subset alone, so it is always automatically compatible with the latest C features without requiring a new 'ObjC standard'.
If the pre- or post-increment behaviour isn't actually needed, I prefer `x += 1` though.
The pre-processor original compiler, before the GCC fork, would leave everything else alone, blindly copying into the generated C file.
It's more code, sure, but it buys you a lot of good things. I/O is hard.
Though I've actually seen macro systems that do things akin to destructors, although less automatically.
For example, the primary reason for the sentence seems to be from the text: "Many code examples in this book won't even compile on a c++ compiler, So we should not mix sources of both languages".
It's not at all about the ability to use c libraries in c++ projects or vice versa :S.... c'mon guys!
This is no longer true. On UEFI systems the only thing you have to do normally is fix the boot order. In fact installing Linux first and Windows second tends to be the better dual-boot strategy nowadays.
Fixing the boot order can be done from UEFI setup, and even from Windows command line
bcdedit /enum firmware
bcdedit /set {fwbootmgr} displayorder {yourlinuxuuid} /addfirst
* is it (*s)++ or *(s++)?
* it is not *++s nor ++*s
*(*s)++
It is concise syntax but very confusing.
I think this is a very lazy and somewhat conspiratorial take.
C++'s IO stream library, along with C++'s adoption of std::string, is a response to and improvement over C's standard library support for IO. That alone makes it an invaluable improvement. It's easy and very lazy to look back 30 years ago and badmouth things done back then.
It's also easy to complain about no one proposing changes when literally anyone, including you, can propose changes. The only need to do the legwork and put their money where their mouth is. The funny part is that we see frameworks putting together their own IO infrastructure and it ends up being not good, such as Qt's take on IO.
But talk is cheap and badmouthing doesn't require a pull request.
template<typename R>
constexpr ssize_t
io::ReadFull(R reader, char *buf, size_t len)
{
ssize_t recvd = 0, ret;
do {
ret = read(reader, &buf[recvd], len - recvd);
if (ret > 0)
recvd += ret;
else
break;
} while (recvd < len);
return recvd;
}
1: https://open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3980.h...
One exception to that in my experience: dependencies, although I think that's a bit deceiving as yes, it's easier to get dependencies in Rust but in some areas they're way less mature and can sometimes be a pain to work with (usually when dealing with big C or C++ libraries that have been quickly glued to a Rust interface to be available in Rust).
cin >> a;
But also ...
sscanf (the_buffer, "%d", &a);
And not being competent in C++ is not great. You are going to be much more productive in C. The feedback loop is much faster, that is, feedback from your designs.
Contrast with Rust which is harder to get going but doesn't require nearly as much to be decent.
Although this may seem cryptic at first sight, the notational convenience is considerable, and the idiom should be mastered, because you will see it frequently in C programs.
https://github.com/fmtlib/fmt is what it's based on, for C++11 and up support.
And no, you don't have to put everything in the header with C++, and especially not if you're using it in "C with classes" mode. C++ only needs it for templates - and even then only if you want to use implicit instantiation, with `extern template` available for fine-grained control allowing you to have those specializations separately compiled and implementations kept out of the header file.
I wonder sometimes why we keep insisting on the "OP ARG, ARG" format in general for assembly. Why not something like `MOV X -> Y` that would make it absolutely clear and unambiguous? For that matter, why not `COPY X -> Y`, since that's what it actually does?