Arrays with length constantly emerge among C users and libraries. They are just all incompatible because without standardization there is no convergence.
I'd argue that linked list might make a better candidate for inclusions, because I've seen the kernel's list.h or similar implementations in many projects and that's stuff is trickier to get right than stuffing a pointer and a size_t in a struct.
When the language standardization body has not managed to add arrays with length in 48 years, I don't think it should be added at this point. The culture is backward looking and incompatible with modern needs and people involved are old and incompatible with the future (no offense, so am I).
C standardization effort should focus on finishing the language, not developing it to match modern world. I have programmed with C over 20 years, since I was a teenager. It's has long been the system programming language I'm most familiar with. For the last 10 years I have never written an executable. Just short callable functions from other languages. Python, Java, Common Lisp, Matlab, and 'horrors or horrors' C++.
I think Standard C's can live next 50 years in gradual decline as portable assembler called from other languages and compilation target.
If I would propose new extension to C language, I would propose completely new language that can be optionally compiled into C and works side by side with old C code.
There are a few somewhat popular languages that fit that description already, and none of them are suitable replacements for C (as far as I've seen). That's not to say there couldn't be a suitable replacement -- just that nobody in a position to do something about it wants the suitable replacement enough for it to have emerged, apparently.
I suspect the first really suitable complete replacement for C would be something like what Checked C [1] tried to be, but a little more ambitious and willing to include wholly new (but perhaps backward-compatible) features (like some of those you've proposed) implemented in an interestingly new enough way to warrant a whole new compile-to-C implementation. Something like that could greatly improve the use cases where a true C replacement would be most appreciated, and still fit "naturally" into environments where C is already the implementation language of choice via a piecemeal replacement strategy where the first step is just using the new language's compiler as the project compiler front end's drop-in replacement (without having to make any changes to the code at all for this first step).
1: https://www.microsoft.com/en-us/research/project/checked-c/
> > using the new language's compiler as the project compiler front end's drop-in replacement (without having to make any changes to the code at all for this first step)
I'll look into Zig more, though. Maybe I'll like it.
---
I stand corrected, given my phrasing. I should have specified that it needs to also support incrementally adding the new language's features while most of the code is still unaltered C, rather than (for instance) having to suddenly replace all the includes and function prototypes just because you want to add (in the case of Zig) an error "catch" clause.
This might come with huge drawbacks, but it still seems like the only socially acceptable way to fully replace C at this time; make it so you can replace it one line of code at a time in existing projects.
typedef struct {
size_t len;
uint8_t data[];
} ByteBuf;
ByteBuf *b = malloc(sizeof(*b) + sizeof(uint8_t) * array_size);
b->len = array_size;
Thing is, you rarely want to share just a buffer anyway. You probably have additional state, locks, etc. So what I do is embed my ByteBuf directly into another structure, which then owns it completely:
typedef struct {
...
ByteBuf mybuffer;
...
} SomeThing;
Makes it easier to take subranges out of it
typedef struct {uint8_t *data, *dataend} With the length you would need to do data += k; length -= k
Especially if you want to use it as safe iterator, you can do data++ in a loop
How would you safely free(data) afterwards? You'd need to keep an alloc'ed pointer somehow.
A possible tiny advantage for this layout is that a pointer to this struct can be used as a pointer to a pointer-to-bytes, without having to adjust it. Although i'm not sure that's not undefined behaviour.
https://github.com/python/cpython/blob/master/Include/object...
Passing a pair of arguments (pointer and a length) is surely one of the more universal conventions among C programmers?
It has been said that design patterns (not just in the GOF sense of the term) are language design smells, implying that when very common patterns emerge it is a de facto popular-uprising call for reform. That, to me, is a more ideal criterion for updating a language standard, but practiced conservatively to avoid too much movement too fast or too much language growth.
On the other hand, I think you might be close to what they meant by "existing practice". I'm just disappointed to find that seems like the probable case (though I think it might also include some convergent evolutionary library innovations by OS devs as well as language features by compiler devs).
In order to uphold that principle, it's important that the standard consider not just "is this useful" but "is this going to be reasonably straightforward for compiler authors to add". Seeing that people have already implemented a feature helps C to avoid landing in the "useful feature which nobody can use because it's not widely available" trap. (For example, C99 made the mistake of adding floating-point complex types in <complex.h> -- but these ended up not being widely implemented, so C11 backed that out and made them an optional feature.)
1. Have 10% of implementations support the feature one way, and 10% support it in an incompatible fashion.
2. Require that all compiler writers invest the time and necessary to support the feature without regard for whether any of their customers would ever use it.
3. Specify that implementations may either support the feature or report that they don't do so, at their leisure, but that implementations which claim to support the feature must do so in the manner prescribed by the Standard.
When C89 was written, the Committee decided that rather than recognizing different categories of implementation that support different sets of features, it should treat the question of what "popular extensions" to support as a Quality of Implementation which could be better resolved by the marketplace than by the Committee.
IMHO, the Committee should recognize categories of Safely Conforming Implementation and Selectively Conforming Program such that if an SCI accepts an SCP, and the translation and execution environments satisfy all documented requirements of the SCI and SCP, the program will behave as described by the Standard, or report in Implementation-Defined fashion an inability to do so, period. Any other behavior would make an implementation non-conforming. No "translation limit" loopholes.
Historically, if there was some action or construct that different implementations would process in different ways that were well suited to their target platforms and purposes, but were incompatible with each other, the Standard would simply regard such an action as invoking Undefined Behavior, so as to avoid requiring that any implementations change in a way that would break existing code. This worked fine in an era where people were used to examining upon precedent to know how implementations intended for certain kinds of platforms and purposes should be expected to process certain constructs. Such an approach is becoming increasingly untenable, however.
If instead the Standard were to specify directives and say that if a program starts with directive X, implementations may either process integer overflow with precise wrapping semantics or refuse to process it altogether, if it starts with directive Y, implementations may either process it treating "long" as a 32-bit type or refuse to process it altogether, etc. this would make it much more practical to write portable programs. Not all programs would run on all implementations, but if many users of an implementation that targets a 64-bit platform need to use code that was designed around traditional microcomputer integer types, a directive demanding that "long" be 32 bits would provide a clear path for the implementation to meet its customers' needs.
That's a good question. I'm not sure I know. I could hazard a guess at what would be "best", but I'm not particularly confident in my thoughts on the matter at this time. As long as how that is handled is thoughtful, practical, consistent, and well-established, though, I think we're much more than halfway to the right answer.
> Historically, if there was some action or construct that different implementations would process in different ways that were well suited to their target platforms and purposes, but were incompatible with each other, the Standard would simply regard such an action as invoking Undefined Behavior, so as to avoid requiring that any implementations change in a way that would break existing code.
If I understand correctly, that would actually be "implementation-defined", not "undefined".
> a directive demanding that "long" be 32 bits would provide a clear path for the implementation to meet its customers' needs
There are size-specific integer types specified in the C99 standard (e.g. `uint32_t`). I use those, except in the most trivial cases (e.g. `int main()`), and limit myself to those size-specific integer types that are "guaranteed" by the standard.
That is an extremely common myth. From the point of view of the Standard, the difference between Implementation Defined behavior and Undefined Behavior is that implementations are supposed to document some kind of behavioral guarantee with regard to the former, even in cases where it would be impractical for a particular implementation to guarantee anything at all, and nothing that implementation could guarantee in those cases would be useful.
The published Rationale makes explicit an intention that Undefined Behavior, among other things, "identifies areas of conforming language extension".
> There are size-specific integer types specified in the C99 standard (e.g. `uint32_t`). I use those, except in the most trivial cases (e.g. `int main()`), and limit myself to those size-specific integer types that are "guaranteed" by the standard.
A major problem with the fixed-sized types is that their semantics are required to vary among implementations. For example, given
int test(uint16_t a, uint16_t b, uint16_t c) { return a-b > c }
Further, if one has a piece of code which is written for a machine with particular integer types, and a compiler which targets a newer architecture but can be configured to support the old set of types, all one would need to do to port the code to the new platform would be to add a directive specifying the required integer types, with no need to rework the code to use the "fixed-sized" types whose semantics vary among implementations anyway.
I think when you get down to the level of C you're looking at the latter much more than the former. C is really more of a platform-agnostic assembler. It's not a design smell to have conventions within the group of language users that are de-facto language rules. For reference, see all the PEP rules about whitespace around different language constructs. These are not enforced.
The whole point of writing a C program is to be close to the addressable resources of the platform, so you'd probably want to expose those low-level constructs unless there's a compelling reason not to. Eliminating an argument from a function by hiding it in a data structure is not that compelling to me since I can just do that on my own. And then I can also pass other information such as the platforms mutex or semaphore representation in the same data structure if I need to.
By the way, that convenient length+pointer array requires new language constructs for looping that are effectively syntactic sugar around the for loop. Or you need a way to access the members of the structure. And syntactic sugar constrains how you can use the construct. So I'm not sure that it adds anything to the language that isn't already there. And the fact that length+pointer is such a common construct indicates that most people don't have any issues with it at all once they learn the language.
Given the prevalence of buffer overflow bugs in computing, I'd say that there are quite a few programmers who have quite a few issues with this concept in practice.
The rest of your arguments are quite sound, but I have to disagree with that one.
In that particular statement at the beginning of my preceding comment, I meant portability across compiler implementations.
> Eliminating an argument from a function by hiding it in a data structure is not that compelling to me since I can just do that on my own.
I meant to refer more to the idea that, when doing it on your own in a particular way, the compiler could support applying a (set of) constraint(s) to prevent overflows (as an example), such that any constraint couldn't be bypassed except by very obviously intentional means. Just automating the creation of the very, very simply constructed "plus a numeric field" struct seems obviously not worth including as a new feature of the standardized language.
> the fact that length+pointer is such a common construct indicates that most people don't have any issues with it
I think you're measuring the wrong kind of problem. Even C programmers with a high level of expertise may have problems with this approach, because it's when programmer error causes a problem not caught by code review or the compiler via buffer overflows (for instance) that we see a need for more.
One alternative to adding types is to allow enforcing consistency in some structs with the trailing array:
struct my_obj {
const size_t n;
//other variables
char text[n];
};
struct my_obj b = {.n = 5};
void * vmalloc(size_t base, size_t var, size_t cnt) {
void *ret = malloc(base + var * cnt);
if (!ret) return ret;
* (size_t *) ret = cnt;
return ret;
}You can't reassign the length variable since it's marked `const`. You should see something like "warning: assignment discards `const` qualifier from pointer target type" if you pass it to `realloc`, which tells you that you're breaking consistency (I guess this might be UB). You could write `vrealloc` to allow resizing such structs, which would probably be called like:
my_obj *tmp = vrealloc(obj, sizeof(obj), sizeof(obj->text), obj->n, newsize);Recognizing common behavioral characteristics would actually improve the usability of arcane hardware platforms if there were ways of explicitly requesting the commonplace semantics when required. For example, if the Standard defined an intrinsic which, given a pointer that is four-byte aligned, would store a 32-bit value with 8 bits per byte little-endian format, leaving the any bits beyond the eighth (if any) in a state which would be compatible with using "fwrite" to an octet-based stream, an octet-based big-endian platform could easily process that intrinsic as a byte-swap instruction followed by a 32-bit store, while a compiler for a 36-bit system could use a combination of addition and masking operations to spread out the bits.
unsigned int x = in[0] + 512*in[1] + 512*512*in[2] + 512*512*512*in[3];
/* aka x = *(int*)in */
out[0] = x & 255; x>>=8;
out[1] = x & 255; x>>=8;
out[2] = x & 255; x>>=8;
out[3] = x & 255;
/* *not* aka *(int*)out = x */Although the Standard defines the behavior of signed-to-unsigned conversion in a way that would yield the same bit pattern as a two's-complement signed number, some compilers will issue warnings if a signed value is implicitly coerced to unsigned. Adding the extra 18 forms would generally require nothing more than defining an extra 24 macros, which seems like a reasonable way to prevent such issues.
Far less bloat than would be needed for a compiler to recognize and optimize any meaningful fraction of the ways people might write code to work around the lack of portably-specified library functions.
Would this involve further specification of bitfields? Feel implementation defined nature of bitfields limits potential
One thing that I'd really like to see would be some new categories of compliance. At present, the definition of "conforming C program" makes it possible to accomplish any task that could be done in any language with a "conforming C program", since the only thing necessary for something to be a conforming C program would be for there to exist some conforming implementation in the universe that accepts it. Unfortunately, the Standard says absolutely nothing useful about the effect of attempting to use an arbitrary conforming C program with an arbitrary conforming C implementation. It also fails to define a set of programs where it even attempts to say much of anything useful about the behavior of a freestanding implementation (since the only possible observable behavior of a strictly conforming program on a freestanding implementation would be `while(1);`).
I would propose defining the terms "Safely Conforming Implementation" and "Selectively Conforming Program" such that feeding any SCP to any SCI, in circumstances where the translation and execution environments satisfy all requirements documented for the program and implementation, would be required not to do anything other than behave as specified, or indicate in documented fashion a refusal to do so. An implementation that does anything else when given a Selectively-Conforming Program would not be Safely Conforming, and a program which a Safely Conforming Implementation could accept without its behavior being defined thereon would not be a Selectively Conforming Program.
While it might seem awkward to have many implementations support different sets of features, determining whether a Safely Conforming Implementation supports all the features needed for a Selectively Conforming Program would be trivially easy: feed the program to the implementation and see if it accepts it.
I think there's a lot of opposition to "optional" features because of a perception that features that are only narrowly supported are failures. I would argue the opposite. If 20% of compilers are used by people who would find a feature useful, having the feature supported by that 20% of compilers, while the maintainers of the other 80% direct their effort toward things other than support for the feature, should be seen as a superior outcome to mandating that compiler writers waste time on features that won't benefit their customers.
Realistically speaking, it would be impossible to define a non-trivial set of programs that all implementations must process in useful fashion. Instead of doing that, I'd say that the question of whether an implementation can usefully process any program is a Quality of Implementation issue, provided that implementations reject all programs that they can't otherwise process in any other conforming fashion.
There are efforts to define the behavior in cases where implementations have converged or died out (e.g., twos complement, shifting into the sign bit).
There have been no proposals to add new array types and it doesn't seem likely at the core language level. C's charter is to standardize existing practice (as opposed to invent new features), and no such feature has emerged in practice. Same for modules. (C++ takes a very different approach.)