<iomanip>: fixes get_time to parse without delimiters

[Arzaghi]

Fixes #944

[Arzaghi]

An irrelevant issue I encountered during fixing this issue. I generally use clang-format extension for Visual Studio and apply the .clang-format file using Tools->Clang Format Document. But this option format these lines as follow:

        const int _Hi_digits = (_Hi <= 9      ? 1
                                : _Hi <= 99   ? 2
                                : _Hi <= 999  ? 3
                                : _Hi <= 9999 ? 4
                                              : static_cast<int>(_STD log10(_STD abs(_Hi))) + 1);

which looks very clear and easy to read.
But the clang-format validation on the sever reject them and expect those lines to be as follow:

STL/stl/inc/xloctime

Lines 542 to 545 in 40f2339

	const int _Hi_digits =
	(_Hi <= 9 ? 1
	: _Hi <= 99 ? 2
	: _Hi <= 999 ? 3 : _Hi <= 9999 ? 4 : static_cast<int>(_STD log10(_STD abs(_Hi))) + 1);

I use the latest version of Clang-Format and the VS extension on my system. I'm wondering about the root of this difference and I'm not sure whether something wrong with a configuration on my system or this happening because of the difference between Clang-Format versions on my system and the server.
By the way, I encountered some other similar minor conflicts on my previous PRs.

[StephanTLavavej]

Different versions of clang-format do change behavior; we are currently using 10.0.0. (Failed clang-format checks will print out the version used; it's the one installed by the VS Preview that we're using.)

In theory, if you're using the same version, and you're using the --style=file option to pick up our .clang-format configuration, the results should be deterministically identical.

[StephanTLavavej]

This looks good to me - I especially like the set of test cases you've crafted. I'll push a change to simplify the _Hi_digits computation and move this forward to Final Review 😸

[CaseyCarter]

Impressively exhaustive tests!

[Arzaghi]

@StephanTLavavej @CaseyCarter
I've added one more tiny (yet important) test case to have better coverage for this scenario.
Excuse me I'm adding this test case at the final stage and after your review and approval.

[StephanTLavavej]

Thanks - both for the additional test case of trailing non-digit characters, and the heads up 😸

[StephanTLavavej]

Thanks again for fixing this widely reported runtime correctness bug! Your fix will ship in VS 2019 16.9 Preview 2. 🐈

[randydu]

The VS 2019 Preview 3 (Visual Studio 2019 Developer Command Prompt v16.9.0-pre.3.0) is installed but the following code cannot parse iso-string properly:

    std::tm tm{0};
    std::istringstream ss(str);
    ss >> std::get_time(&tm, "%Y%m%dT%H%M%S");
    if (ss.fail())
        throw std::invalid_argument("Invalid argument: " + str);

   //str = "19700101T000001"

Expected:

  CHECK(tm.tm_sec == 1); //should be 1 second
  CHECK(tm.tm_min == 0);

Actual:

  CHECK(tm.tm_sec == 0);
  CHECK(tm.tm_min == 1); // 1 min ?

The same test works fine for gcc and clang.