string_view | A string_view implementation that can remember
kandi X-RAY | string_view Summary
kandi X-RAY | string_view Summary
A string_view implementation that can remember if it was a c-string once
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QUESTION
In RAII(Resource Acquisition Is Initialization), an object obtain piece of resource is the procedure of initialization itself, and resource will be held as life cycle of object, but resource in string_view only includes char * and size, which means the address could be free to invalidation and object couldn't be conscious about it. And does it make the object never closure?
...ANSWER
Answered 2021-Jun-15 at 08:05std::string_view doesn't Acquire Resource, it is not a RAII object.
QUESTION
#include
#include
#include
using namespace std::literals;
int main()
{
auto fn_is_l = [](auto const c) { return c == 'l'; };
{
auto v = "hello"sv | std::views::filter(fn_is_l);
std::cout << *v.begin() << std::endl; // ok
}
{
auto const v = "hello"sv | std::views::filter(fn_is_l);
std::cout << *v.begin() << std::endl; // error
}
}
ANSWER
Answered 2021-May-24 at 06:17In order to provide the amortized constant time complexity required by range, filter_view::begin caches the result in *this. This modifies the internal state of *this and thus cannot be done in a const member function.
QUESTION
I'd like to implement a non-copy data trim_left function, but would like to not allow it to accept temporary parameters to make the returned string_view is valid (the data is still alive). I started accepting string_view as parameter, but I cannot get the way how to guarantee the data is valid.
So I make this:
...ANSWER
Answered 2021-May-23 at 21:33Well... given that trim_left() doesn't change data, I suppose that you can write the main trim_left() receiving a T const &
QUESTION
I have this constexpr class:
...ANSWER
Answered 2021-May-20 at 23:08This is nothing to do with lambdas. The actual error message from clang - just compiling your class, without even trying to instantiate it - is:
'function' is not literal because it is not an aggregate and has no constexpr constructors other than copy or move constructors
which is pretty much self-explanatory.
You can work around this if it's OK for onValue to be a plain-old function pointer. The following code compiles correctly (but would not work with a capturing lambda):
QUESTION
How to write the following so-called mini-reproducable example in which the begin iterator may be constract either on the base of std::string_view or std::string.
So, let's say that we have the following programme:
...ANSWER
Answered 2021-May-17 at 16:30You're thinking way too deeply. You don't need the template parameters; the type you're trying to test against is the same type as it. So just use that:
QUESTION
I'm struggling to get boost's stack trace library to interoperate with fmt, the trouble seems to be that I can't quite specialize a boost::stacktrace::basic_stacktrace. Anybody know what the underlying issue is?
...ANSWER
Answered 2021-May-14 at 19:28Just three small things:
Missing/wrong headers. You need to include
fmt/ranges.hin order to support formatting ranges.Wrong overload. The function for formatting into an iterator is
fmt::format_to, notfmt::format.These:
QUESTION
I have a question because it is not clear to me when function arguments get destroyed. Therefore, is the concatenation of the following doSomething function error-prone or not?
I’m asking because "it is the programmer's responsibility to ensure that std::string_view does not outlive the pointed-to character array". Can that be guaranteed in that specific case or not?
...ANSWER
Answered 2021-May-13 at 14:48The anonymous temporary passed to the (const reference) parameter const std::string_view& str_view survives the function call.
Since there are nested functions, the anonymous temporaries are not destroyed until, conceptually, the closing semicolon of
QUESTION
Is there a way to create index tuple with compile-time known size like
...ANSWER
Answered 2021-May-10 at 20:58pass a sequence of ints 0, 1, 2, 3, ..., 99 to [function arguments]
You don't need tuples. Do this:
QUESTION
#include
#include
#include
using namespace std::literals;
int main()
{
auto v1 = std::set>{"abc"s};
v1.contains("abc"s); // ok
v1.contains("abc"sv); // ok
auto v2 = std::set{"abc"s};
v2.contains("abc"s); // ok
v2.contains("abc"sv); // error
}
ANSWER
Answered 2021-May-09 at 10:03My guess is because they thought it wasn't so great improvement to break backward compatibility.
Another reason is because std::set with std::less existed even before C++11 (starting from C++03 I guess) and std::less<> appeared only in C++14. So if they move to std::set with std::less<> then you have to force C++14 when using set, or you have to make two kinds of sets - one for C++03 and one for C++14.
Also if you start from C++14 making set being std::less<>-based then your pre-C++14 code will start to behave differently sometimes. For example your code relied on calling Key's constructor for some reason when adding to set, then suddenly if you add option -std=c++14 your old code starts doing other things.
Usually STD people make such changes that switching from C++11 to C++14 doesn't break code's behaviour. Only downswitching from C++14 to C++11 can break something(usually non-compiling). In other words it is backward compatibility breaking change to use std::less<>. Such changes are usually only done by introducing new class name for such specializations.
QUESTION
I try to compile a personal project on Visual Studio 2019 (using MSVC 19.28 compiler) and I came accross a compilation error in the std::visit which I don't understand:
ANSWER
Answered 2021-May-08 at 21:38It seems MSVC is having difficulty synthesizing a lambda with a pointer-to-member argument in a template context.
I tried to simplify it to a MCVE, hopefully it captures the essence of the issue:
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