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Why does C have the best file API

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Re: Why does C have the best file API

#101

Post by ddtaylor »

josefx wrote: post #99
johannes1234321 wrote: post #95

Earlier quoted context omitted.

That is not C, but a non-standard extension and thus not portable.

> non-standard extension and thus not portable Modern versions of standard C aren't very portable either, unless you plan to stick to the original version of K&R C you have to pick and choose which implementations you plan to support.

I disagree. Modern C with C17 and C23 make this less of an issue. Sure, some vendors suck and some people take shortcuts with embedded systems, but the standard is there and adopted by GCC, Clang and even MSVC has shaped up a bit.

Re: Why does C have the best file API

#102

Post by josefx »

lifthrasiir wrote: post #60
Negitivefrags wrote: post #58

Earlier quoted context omitted.

Why is it such a terrible idea? No need to add complexity, dependancies and reduced performance by using these libraries.

No defined binary encoding, no guarantee about concurrent modifications, performance trade-offs (mmap is NOT always faster than sequential reads!) and more.

Doesn't that just describe low level file IO in general?

Re: Why does C have the best file API

#103

Post by josefx »

ddtaylor wrote: post #101
josefx wrote: post #99

Earlier quoted context omitted.

> non-standard extension and thus not portable Modern versions of standard C aren't very portable either, unless you plan to stick to the original version of K&R C you have to pick and choose which implementations you plan to support.

I disagree. Modern C with C17 and C23 make this less of an issue. Sure, some vendors suck and some people take shortcuts with embedded systems, but the standard is there and adopted by GCC, Clang and even MSVC has shaped up a bit.

> GCC, Clang and even MSVC

Well, if that is the standard for portability then may_alias might as well be standard. GCC and Clang support it and MSVC doesn't implement the affected optimization as far as I can find.

Re: Why does C have the best file API

#104

Post by karel-3d »

In go, you can do mmap with some help of external library :) you can mmap a file - https://github.com/edsrzf/mmap-go - and then unsafe-retype that to slice of objects, and then read/write to it. It's very handy sometimes!

It's unsafe though.

You also need to be careful to not have any pointers in the struct (so also no slices, maps); or if you have pointers, the must be nil. Once you start unsafe-retyping random bytes to pointers, thing explode very quickly.

So maybe this article has a point.

Re: Why does C have the best file API

#105

Post by lelanthran »

dataflow wrote: post #48
dekhn wrote: post #33

Earlier quoted context omitted.

Address space size and RAM are two different things.

What they said is correct regardless of that though?

> What they said is correct regardless of that though?

I don't think so.

Their post is basically:

>> It still works if the file doesn't fit in RAM

> No it doesn't.

Which is incorrect: it actually does work for files that don't fit in RAM. It doesn't work only for files that don't fit in the address space, which is not what the author claimed.

Re: Why does C have the best file API

#106

Post by ddtaylor »

josefx wrote: post #103
ddtaylor wrote: post #101

Earlier quoted context omitted.

I disagree. Modern C with C17 and C23 make this less of an issue. Sure, some vendors suck and some people take shortcuts with embedded systems, but the standard is there and adopted by GCC, Clang and even MSVC has shaped up a bit.

> GCC, Clang and even MSVC Well, if that is the standard for portability then may_alias might as well be standard. GCC and Clang support it and MSVC doesn't implement the affected optimization as far as I can find.

What do you think the standard is for standardization?

Re: Why does C have the best file API

#107

Post by lionkor »

Negitivefrags wrote: post #66
amluto wrote: post #61

Earlier quoted context omitted.

Lots of reasons: The code is not portable between architectures. You can’t actually define your data structure. You can pretend with your compiler’s version of “pack” with regrettable results. You probably have multiple kinds of undefined behavior. Dealing with compatibility between versions of your software is awkward at best. You might not even get amazing performance. mmap is not a panacea. Page faults and TLB flu…

I've written a lot of code using that method, and never had any portability issues. You use types with number of bits in them. Hell, I've slung C structs across the network between 3 CPU architectures. And I didn't even use htons! Maybe it's not portable to some ancient architecture, but none that I have experienced. If there is undefined behavior, it's certainly never been a problem either. And I've seen a lot of ta…

That seems highly unlikely. Let's assume that all compilers use the exact same padding in C structs, that all architectures use the same alignment, and that endianness is made up, that types are the same size across 64 and 32 bit platforms, and also pretend that pointers inside a struct will work fine when sent across the network; the question remains still: Why? Is THIS your bottleneck? Will a couple memcpy() operations that are likely no-op if your structs happen to line up kill your perf?

Re: Why does C have the best file API

#109

Post by t-3 »

ajross wrote: post #20
seba_dos1 wrote: post #3

mmap is not a C feature, but POSIX. There are C platforms that don't provide mmap, and on those that do you can use mmap from other languages (there's mmap module in the Python's standard library, for example).

I think this is sort of missing the point, though. Yes, mmap() is in POSIX[1] in the sense of "where is it specified". But mmap() was implemented in C because C is the natural language for exposing Unix system calls and mmap() is a syscall provided by the OS. And this is true up and down the stack. Best language for integrating with low level kernel networking (sockopts, routing, etc...)? C. Best language for async I…

>> Best language for SIMD integration? C

Uh, no. C intrinsics are so much worse than just writing assembly that it's not even comparable.

Re: Why does C have the best file API

#110

Post by zombot »

gopalv wrote: post #64
amluto wrote: post #55

I can’t entirely tell what the article’s point is. It seems to be trying to say that many languages can mmap bytes , but: > (as far as I'm aware) C is the only language that lets you specify a binary format and just use it. I assume they mean: struct foo { fields; }; foo *data = mmap(…); And yes, C is one of relatively few languages that let you do this without complaint, because it’s a terrible idea . And C doesn’t…

> correspond to a binary format in accordance with the C ABI on your particular system. We're so deep in this hole that people are fixing this on a CPU with silicon. The Graviton team made a little-endian version of ARM just to allow lazy code like this to migrate away from Intel chips without having to rewrite struct unpacking (& also IBM with the ppc64le). Early in my career, I spent a lot of my time reading Java b…

Fuck, the stupidity of humans really is infinite.
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