Problem:
- gcc-8 gives the following error when compiling this function on all
standards:
test/std-format-test.cc: In member function 'constexpr auto std::formatter<S>::parse(std::format_parse_context&)':
test/std-format-test.cc:112:17: error: call to non-'constexpr' function 'int isdigit(int)'
if (!isdigit(c) || (++iter, get_char()) != '}')
~~~~~~~^~~
Solution:
- Write a `constexpr` version of `isdigit` for use in this function.
Co-authored-by: Jonathan Gopel <jgopel@quantlab.com>
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