Re: [PATCH] libstdc++: Fix build failure due to missing <langinfo.h> [PR98374]

[Patrick Palka <ppalka@redhat.com>]

On Fri, Dec 18, 2020 at 11:04 AM Patrick Palka <ppalka@redhat.com> wrote:
>
> This fixes a build failure on Windows which lacks <langinfo.h>.
> (We can't use the more portable localeconv() from <clocale> to obtain
> the radix character of the current locale here because it's not
> thread-safe, unfortunately.)
>
> This change means that on Windows and other such systems, we'll just
> always assume the radix character used by printf is '.' when formatting
> a long double through it.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/98374
>         * src/c++17/floating_to_chars.cc: Guard include of <langinfo.h>
>         with __has_include.
>         (__floating_to_chars_precision) [!defined(RADIXCHAR)]: Don't
>         attempt to obtain the radix character of the current locale,
>         just assume it's '.'.

I went ahead and committed this patch under the "obvious" rule as r11-6259.

> ---
>  libstdc++-v3/src/c++17/floating_to_chars.cc | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/src/c++17/floating_to_chars.cc b/libstdc++-v3/src/c++17/floating_to_chars.cc
> index 474e791e717..6470fbb0b95 100644
> --- a/libstdc++-v3/src/c++17/floating_to_chars.cc
> +++ b/libstdc++-v3/src/c++17/floating_to_chars.cc
> @@ -33,7 +33,9 @@
>  #include <cmath>
>  #include <cstdio>
>  #include <cstring>
> -#include <langinfo.h>
> +#if __has_include(<langinfo.h>)
> +# include <langinfo.h> // for nl_langinfo
> +#endif
>  #include <optional>
>  #include <string_view>
>  #include <type_traits>
> @@ -1113,6 +1115,7 @@ template<typename T>
>         // to handle a radix point that's different from '.'.
>         char radix[6] = {'.', '\0', '\0', '\0', '\0', '\0'};
>         if (effective_precision > 0)
> +#ifdef RADIXCHAR
>           // ???: Can nl_langinfo() ever return null?
>           if (const char* const radix_ptr = nl_langinfo(RADIXCHAR))
>             {
> @@ -1121,6 +1124,7 @@ template<typename T>
>               // UTF-8 character) wide.
>               __glibcxx_assert(radix[4] == '\0');
>             }
> +#endif
>
>         // Compute straightforward upper bounds on the output length.
>         int output_length_upper_bound;
> --
> 2.30.0.rc0
>