std::format can't format std::chrono::time_point

[tardy dagger]

So I have this piece of code:

auto time_now = std::chrono::system_clock::now();
auto time_delta = duration->to_seconds();
auto future = time_now + time_delta;
auto future_str = std::format("{}", future);

However, in the last line, I get the following error:

In template: call to deleted constructor of 'typename format_context::formatter_type<time_point<system_clock, duration<long long, ratio<1, 1000000>>>>' (aka 'formatter<std::chrono::time_point<std::chrono::system_clock, std::chrono::duration<long long, std::ratio<1, 1000000>>>, char>') error occurred here while substituting into a lambda expression here in instantiation of function template specialization 'std::basic_format_arg<std::format_context>::handle::handle<std::chrono::time_point<std::chrono::system_clock>>' requested here in instantiation of function template specialization 'std::basic_format_arg<std::format_context>::basic_format_arg<std::chrono::time_point<std::chrono::system_clock>>' requested here in instantiation of function template specialization 'std::make_format_args<std::format_context, std::chrono::time_point<std::chrono::system_clock>>' requested here in instantiation of function template specialization 'std::format<std::chrono::time_point<std::chrono::system_clock>>' requested here 'formatter' has been explicitly marked deleted here

I'm aware that I have to set a time format for it (per this SO post and this one), however doing any of those (i.e std::format("{:%Y-%m-%d %X}", future);) doesn't make the error disappear.

[queen flower]

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[left crown]

https://en.cppreference.com/w/cpp/utility/format/formatter#Standard_specializations_for_library_types I don't see timepoint there

I think you need to convert it to another type first

https://en.cppreference.com/w/cpp/chrono/time_point/time_since_epoch can get it as a duration (which is formattable)

actually wait

no should work

hmmm

https://en.cppreference.com/w/cpp/chrono/system_clock/formatter it does have one

[tardy dagger]

Isn't it weird?

It also didn't have this issue with fmt

that to_seconds type is std::chrono::seconds

fyi

[lean horizon]

;compile -std=c++23 ```cpp
#include <chrono>
#include <format>
#include <iostream>

std::string foo(std::chrono::seconds time_delta) {
auto time_now = std::chrono::system_clock::now();
auto future = time_now + time_delta;
return std::format("{}", future);
}

int main() {
using namespace std::literals;
std::cout << foo(123s);
}

[pallid nacelle]

Program Output

2024-01-02 10:10:07.959272101

wreien | 122ms | c++ | x86-64 gcc 13.2 | godbolt.org

[lean horizon]

seems to work fine, what compiler/version?

[tardy dagger]

Clangd 18

It's clangd that's giving me this error

[lean horizon]

Clang with libstdc++, libc++, or MSVC STL?

(checking with libstdc++ and libc++ both work for me)

[tardy dagger]

It's not MSVC STL

I'm on linux

[lean horizon]

If you're on linux and you haven't specified explicitly to use libc++, then it's probably using whatever version of libstdc++ you have installed

Which you can check with g++ --version

(there are macros it defines too otherwise)

But in that case it's quite likely that the version is too old

(though that would surprise me I think? GCC13 was the first with text formatting at all...)

Perhaps it's clangd doing something weird and falling over

[tardy dagger]

Weirdly enough I'm using the clang compiler with I believe libsc++ lib
Cause apparently libstdc++ is very behind when it comes to C++20

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++20 -stdlib=libc++  -fexperimental-library -v")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -std=c++20 -stdlib=libc++ -fexperimental-library -lc++-abi")

I got this in my CMake Lists

[lean horizon]

I'm pretty sure libstdc++ is further ahead than libc++

But OK, yes, looks like you're using libc++ (whichever version you have installed, I assume trunk by '18'?)

[tardy dagger]

Should I switch back to libstdc++?

[tardy dagger]

My compiler version is 17 (tho a compiled version from the clang 16 days)
My clangd version is 18 (shipped with CLion)

[tardy dagger]

I probably should switch back to libstdc++ cause it's what most linux C(++) libs are compiled with