Hi Sebastian

You've got me converted to std::format !

I like what you said that it formats by default with {} so no duplicate
of me needing to match %s or such to particular parameters. Also I like
that it is reversible.

I imagine the compiler will be able to check the variadic parameters
match what is expected, eg like at present for the conventional approach.

std::string str_fmt(const char * const format, ...) __attribute__
((format (printf,1,2)));

Jonny

On 20/07/2019 23:17, Sebastian Büttner via Std-Proposals wrote:
> Hi again Jonny,
>
> just to come back to your original example and to clearify things:
> std::format is supposed to replace not only your missing
> "to_string(bool)" but to process the entire formatting in your example.
> So you example might become:
>
> std::string fmt(const std::string header, bool b)
> {
> return std::format("{} {} set", header, b);
> }
>
> Cheers,
> Sebastian
>
> On 2019-07-21 00:03, Sebastian Büttner via Std-Proposals wrote:
>> Hi Jonny,
>>
>> std::format origins from libfmt (https://github.com/fmtlib/fmt/). The
>> syntax is related to other format libraries that have prooven useful
>> like pythons string.format for example.
>>
>> The main goal is to get the typesafety from iostreams but the
>> convenient format strings of printf like approaches.
>>
>> Booleans are by default formatted with their textual representation
>> (true|false), so the following is sufficient:
>>
>> std::string s = std::format("{}", true);
>>
>> which is kinda neat :) (you do not need type information within the
>> formatting string which is great for typesafety!)
>>
>> Cheers,
>> Sebastian
>>
>> On 2019-07-20 23:51, Jonny Grant via Std-Proposals wrote:
>>
>>> Hi Garrett
>>>
>>> Many thanks for the reply with link.
>>>
>>> std::format could be good good, I hadn't heard. Currently I had
>>> always needed to use my own variadic std::string str_sprintf().
>>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r9.html#Syntax
>>>
>>>
>>> Saw this
>>> std::string s = std::format("{:s}", true);
>>>
>>> It looks like different syntax to printf % style is being used.
>>> Don't think that is ideal...
>>> But at least bool is in..
>>>
>>> Cheers, Jonny
>>>
>>> On 20/07/2019 22:24, Garrett May via Std-Proposals wrote:
>>>
>>> Hi Jonny,
>>>
>>> With respect to std::to_string, please see a reference to it here:
>>> https://en.cppreference.com/w/cpp/string/basic_string/to_string
>>>
>>> std::to_string appears to be defined specifically for primitive
>>> numeric types that match up to using sprintf and a format specifier.
>>> I don't think that std::to_string(bool) would be suitable, as it
>>> does not have a format specifier like the others. And there is also
>>> the possibility that when converting a bool to a string that the
>>> user genuinely want '0' or '1' to be produced, as they may be trying
>>> to handle the result as data.
>>>
>>> As Jake said, there is a format library coming out for C++20. That
>>> sounds like a more desirable way to handle this problem, as like I
>>> mentioned, choosing how one wants a bool to be represented textually
>>> is similar to how one would want a float or a double represented
>>> textually.
>>>
>>> Regards,
>>>
>>> Garrett
>>>
>>> On Sat, 20 Jul 2019, 21:39 Jonny Grant via Std-Proposals,
>>> <std-proposals_at_[hidden]> wrote:
>>> Hi Garrett
>>>
>>> Many thanks for your reply.
>>>
>>> Yes, I see std::boolalpha sets an I/O flag.. but seems a bit of a
>>> long way to get it into a string, I'd need to use in conjunction
>>> with std::istringstream to get a string...
>>>
>>> I wanted to do something like this example:
>>>
>>> IDEA
>>> std::string fmt(const std::string header, bool b)
>>> {
>>> return header + " " + std::to_string(b) + " set";
>>> }
>>>
>>> HOW I WOULD DO NOW
>>> As his doesn't work, I'd have it at present as:
>>> std::string fmt(const std::string header, bool b)
>>> {
>>> return header + " " + b?"true":"false" + " set";
>>> }
>>>
>>> Regards, Jonny
>>>
>>> On 20/07/2019 21:21, Garrett May via Std-Proposals wrote:
>>>
>>> std::boolalpha is already available:
>>>
>>> int main(){
>>> bool const a = true;
>>> std::cout << std::boolalpha << a << std::endl;
>>> }
>>>
>>> My gut instinct here is that one is supposed to control how one
>>> wants data to be printed out, in the same way as how float/double
>>> precision is done.
>>>
>>> On Sat, 20 Jul 2019, 21:16 Jonny Grant via Std-Proposals,
>>> <std-proposals_at_[hidden]> wrote: Hello
>>>
>>> Could std::string to_string(bool value); be added? Currently it
>>> outputs
>>> as a number due to the implicit conversion to int?
>>> Feel it would have been more appropriate as "true" or "false".
>>>
>>> http://www.cplusplus.com/reference/string/to_string/
>>>
>>> $ g++-8 -Wall -o to_string to_string.cpp
>>> $ ./to_string
>>> 1
>>>
>>> // g++-8 -Wall -o to_string to_string.cpp
>>> #include <string>
>>> #include <iostream>
>>> int main()
>>> {
>>> const bool a = true;
>>> const std::string b(std::to_string(a));
>>> std::cout << b << std::endl;
>>> }
>>>
>>> Cheers, Jonny
>>>
>>> .
>>>
>>> --
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>>> http://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
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