Cannot use std::chrono::parse even with -std=c++2a and g++-11

Question

When trying to compile the following example:

std::chrono::sys_time<std::chrono::microseconds> timestamp; std::stringstream ss = foo(); ss >> std::chrono::parse("%Y-%m-%d %T", timestamp);

I get:

error: ‘parse’ is not a member of ‘std::chrono’ 15 | ss >> std::chrono::parse("%Y-%m-%d %T", timestamp); | ^~~~~

I was not expecting this, as I'm using the latest g++ I could find.

More info:

$ g++-11 --version g++-11 (Ubuntu 11.1.0-1ubuntu1~18.04.1) 11.1.0 $ g++-11 -v Using built-in specs. COLLECT_GCC=g++-11 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: (...) Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~18.04.1)

I'm compiling with:

g++-11 -std=c++2a -o test time.cc

Is this just not supported in g++-11.1.0?

Does GCC advertise support for this in its standard library? — Qaz
– Qaz, Commented Aug 12, 2021 at 11:40
Possibly a duplicate question of stackoverflow.com/questions/67906096/… ? — Yun
– Yun, Commented Aug 12, 2021 at 11:51
see en.cppreference.com/w/cpp/compiler_support, only visual studio has a complete implementation (search for "Calendar and timezone") — Alan Birtles
– Alan Birtles, Commented Aug 12, 2021 at 13:18
Dammit. I find it so frustrating that there's no default way in C or C++ to parse a timestamp with microsecond precision. I ended up rolling my own with sscanf writing into a struct tm for all fields except for ts_sec, which I set to zero. Then I use timegm to get the timestamp in seconds, and add things up with a float that I parse in scanf for number of seconds (taking in to account the units ofc). — amsterdam
– amsterdam, Commented Aug 12, 2021 at 13:21

Howard Hinnant · Accepted Answer · 2021-08-12 15:02:55Z

9

Until your favorite C++ vendor ships std::chrono::parse, there exists a free, open-source preview of this part of C++20.

std::chrono::sys_time<std::chrono::microseconds> timestamp; std::stringstream ss = foo(); ss >> date::parse("%Y-%m-%d %T", timestamp);

answered Aug 12, 2021 at 15:02

Howard Hinnant

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2 Comments

doraemon Over a year ago

which part corresponds to the support of this in en.cppreference.com/w/cpp/compiler_support? will it be supported in gcc13?

Howard Hinnant Over a year ago

Search for "Calendar" at that link.

margothequeen · Accepted Answer · 2024-02-13 22:58:04Z

0

well i have a g++ 13.2.0 and this is a part of its chrono

#if __cplusplus >= 202002L // TODO formatting and parsing // # undef __cpp_lib_chrono // # define __cpp_lib_chrono 201907L #endif

answered Feb 13, 2024 at 22:58

margothequeen

1

5 Comments

Howard Hinnant Over a year ago

g++ 14 will ship with full C++20 chrono support. One can experiment with it today at wandbox.org.

Alvov1 Jun 14 at 8:43

g++ 14.3 does not contain chrono::parse, and even 15.1 does not. Can't believe it's been 5 years already, and still there is no release version for this??

Howard Hinnant Jun 14 at 13:56

Compiler Explorer appears to indicate that you are mistaken: gcc.godbolt.org/z/cEdj4q6fE

gast128 Nov 21 at 16:49

Perhaps add -std=c++20

Warpstar22 Over a year ago

I would recommend editing this and explaining what that commented code means

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