@programminginc - страница 3895

Abbasi

But how they're faster than std::map? By the way how are the key kept unique?

Vlad

No, C casts can cast away and cast in const and volatile

It's a problem only for references, no?

Vlad

https://godbolt.org/z/GE6E6n7ro

Ludovic 'Archivist'

Your suggestion is to use arrays instead of the std::map?

Yes, std::map is overkill, it is pretty expensive to build, and pretty expensive to look up it. std::map will evict log(n) cache lines when doing your lookup for the value, as well as disrupt the branch predictor, while using an array will literally compile the lookup to one instruction

Vlad

https://godbolt.org/z/GE6E6n7ro

Both c cast and static_cast here remove cv for values

Ludovic 'Archivist'

It's a problem only for references, no?

Yes, I just want them to take good habits in case they work with templates in the future

Ludovic 'Archivist'

Both c cast and static_cast here remove cv for values

Nope, here it does a copy

Vlad

Yes, I just want them to take good habits in case they work with templates in the future

I see, I just find them to be too verbose for usercode value casting tbh

Vlad

Nope, here it does a copy

Where? Asm is identical

Ludovic 'Archivist'

Where? Asm is identical

of course it is, here it does a copy in both case

Ludovic 'Archivist'

Where? Asm is identical

https://godbolt.org/z/YrxnTvbd9

Vlad

Yeah, I'm talking about values though, not references. For references C casts are deadly yeah

Vlad

Not denying that

Ludovic 'Archivist'

Yeah, I'm talking about values though, not references. For references C casts are deadly yeah

Yes, it is a question of not getting bad habits. Basically code hygiene. I write a lot of templates and a wrongly placed C-cast can take quite a few week to debug

Vlad

Yes, it is a question of not getting bad habits. Basically code hygiene. I write a lot of templates and a wrongly placed C-cast can take quite a few week to debug

Thankfully I do not contribute to your code base

Ludovic 'Archivist'

Thankfully I do not contribute to your code base

What a coincidence, I was thinking the same

Pavel

Thankfully I do not contribute to your code base

Is there any benefit of using c-cast apart from it being shorter?

Vlad

Is there any benefit of using c-cast apart from it being shorter?

No, just shortness and readability

Pavel

Readability is controversial. I feel like c-casts are easier to hide in other code

Ludovic 'Archivist'

Readability is controversial. I feel like c-casts are easier to hide in other code

Yeah, very hard to grep for

Pavel

I think in about all projects I worked on c-casts were banned

Pavel

And reinterpret_cast as well

Vlad

seeing code related makes me nauseous a little bit int a = ...; int b = ...; foobar(static_cast<size_t>(a), static_cast<short>(b));

Vlad

Cant help it

Pavel

The code is clearly showing that there is a possibility to lose some data here, which I think is good

Vlad

The code is clearly showing that there is a possibility to lose some data here, which I think is good

So does the C cast

Vlad

But it aint 40 symbols

Ludovic 'Archivist'

So does the C cast

How do you look up C-casts in your code base?

Vlad

How do you look up C-casts in your code base?

If you have a specific type in mind you just literally ctrl+f/grep it. Again why would you look up c casts for values?

Vlad

I get why would you grep reinterpret casts or const casts

Ludovic 'Archivist'

If you have a specific type in mind you just literally ctrl+f/grep it. Again why would you look up c casts for values?

How do you know if your C cast applies to a value for sure if you are in a templated function/class

Cayetano

Guys, I guess that you are mixing C and C++. I'm convinced that C++ is enough optimized to use STL and resolve the issues that you are mention... isn't it?

Vlad

How do you know if your C cast applies to a value for sure if you are in a templated function/class

You don't use it with a template

Vlad

With like a typename

Vlad

Obviously

Ludovic 'Archivist'

Guys, I guess that you are mixing C and C++. I'm convinced that C++ is enough optimized to use STL and resolve the issues that you are mention... isn't it?

The STL will not save you from using the wrong datastructure for the job

Pavel

Guys, I guess that you are mixing C and C++. I'm convinced that C++ is enough optimized to use STL and resolve the issues that you are mention... isn't it?

Are you referring to the std::map conversation?

Cayetano

The STL will not save you from using the wrong datastructure for the job

Of course... that's true

Vlad

Obviously

But static casting ints is just pointless

Cayetano

Are you referring to the std::map conversation?

I'm referencing that in C++ you can optimize the code in same way what we did with C

Vlad

I'm referencing that in C++ you can optimize the code in same way what we did with C

Yeah but it takes you not being "Ooow, std::map, shiny"

Vlad

And then putting std::vector's into std::map

Cayetano

Well, the only way that I find to solve my situation is that, because, if I implement the solution suggested by @Abbasi_dev, that is (following message)

Cayetano

. . . enum class languages { es_AR,es_BO,es_CL,es_CO,es_CR,es_DO,es_EC,es_ES,es_GT, ... }; const std::map<languages, const char *> languagesNames{ {languages::es_AR, "Spanish (Argentina)"}, {languages::es_BO, "Spanish (Bolivia)"}, {languages::es_CL, "Spanish (Chile)"}, .... }; ```

Vlad

Well, the only way that I find to solve my situation is that, because, if I implement the solution suggested by @Abbasi_dev, that is (following message)

Usually localization is done via resource files that then get embedded into the executable

Cayetano

I get from system a string like "es_ES" or "en_US", and I need to find the match in the enum... How can I do that?

Vlad

Usually localization is done via resource files that then get embedded into the executable

And all of the stuff above it does itself, you only supply it with your locale and string_id of your phrase

Cayetano

Usually localization is done via resource files that then get embedded into the executable

Of course, that part is clear for me...

Abbasi

Well, the only way that I find to solve my situation is that, because, if I implement the solution suggested by @Abbasi_dev, that is (following message)

Whether an array is faster than a std::map depends on many factors, especially for such small maps. Also, using the map you can have the keys unique, as mentioned.

Cayetano

Even if you choose the path to store in a file and load it dinamically... That part I guess that I have clear...

Ludovic 'Archivist'

I get from system a string like "es_ES" or "en_US", and I need to find the match in the enum... How can I do that?

with an extra array for those mappings, using the property of the iso language strings to compress the 5 byte string into a uint32_t and mapping that to the enums

Cayetano

My issue now is, you get from system a string (char*) and you need to find out how to match it to the enum or std::map structures...

Cayetano

Whether an array is faster than a std::map depends on many factors, especially for such small maps. Also, using the map you can have the keys unique, as mentioned.

OK, that is true! And I plan to use std::map...

Cayetano

But the enum part is what I cannot see clear

Vlad

with an extra array for those mappings, using the property of the iso language strings to compress the 5 byte string into a uint32_t and mapping that to the enums

Would work with std::find after that

Abbasi

You can always measure.

Ludovic 'Archivist'

Would work with std::find after that

Yep

Vlad

Which will be totally fine since not like he's gonna have more than 10 languages

Cayetano

with an extra array for those mappings, using the property of the iso language strings to compress the 5 byte string into a uint32_t and mapping that to the enums

So, are you saying to have a map, an array and a enum to keep the same that I have with only one map and a bunch of #defines? 🤔

Ludovic 'Archivist'

So, are you saying to have a map, an array and a enum to keep the same that I have with only one map and a bunch of #defines? 🤔

No map

Ludovic 'Archivist'

why would you use a map

Ludovic 'Archivist'

No defines either

Cayetano

Just a std::map<string, string> to store pairs like {'en_US', 'American English'}?

Ludovic 'Archivist'

just std::array, a reinterpret_cast and enum to int convertions

Ludovic 'Archivist'

Just a std::map<string, string> to store pairs like {'en_US', 'American English'}?

Stop using std::map at all, it is literally deleting your braincells

Cayetano

Sorry I'm a little bit newbie, how can I use a reinterpret_cast and enum? 🤔 Can you show me briefly, please 🙏?

Ludovic 'Archivist'

enum and enum class are stored in memory as integers, size is system dependent but is always less than that of size_t. enum and enum class values start at 0 and go incrementing by one each time. By having an array that is ordered exactly like the enum members, you can take that array and do the_array[static_cast<size_t>(enum_value)] to map an enum to a value without requiring any extra memory fetch

@cayetanohosma I did already

Cayetano

@cayetanohosma I did already

Oh! sorry, let's me see...

Ludovic 'Archivist'

as for the reinterpret cast, look at those language strings and find the character that is so redundant you could remove it

Vlad

So, are you saying to have a map, an array and a enum to keep the same that I have with only one map and a bunch of #defines? 🤔

struct Lang { uint32_t code; char description[28]; }; Lang langs[147]; auto lang = std::find_if(std::begin(langs), std::end(langs), [](auto& l){ return l.code == 0xB00B5: });

Vlad

Although I would go for char[6] instead

Ludovic 'Archivist'

Although I would go for char[6] instead

At least use a char[8], no need to put weird alignment in here

Vlad

At least use a char[8], no need to put weird alignment in here

It's a struct anyway you can add those 2 bytes to the next member

Vlad

Yeah load store would take 2 instructions rather than 1, don't care really

Vlad

It's a language select not a video decoder