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Declare the namespace-scope constants in to_chars.hpp inline - #5776
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MSVC warns with C5260 that kAlpha and kGamma have internal linkage when the header is used as a header unit or through a module. JSON_INLINE_VARIABLE makes them inline variables from C++17 on. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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added this pull request to stack #5778
October 7, 2026 07:02
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MSVC reports warning C5260 ("the constant variable … has internal linkage in an included header file context, but external linkage in imported header unit context") for
to_chars.hppwhen the library is used as a header unit or through a module, see #4826.The warning comes from
kAlphaandkGamma, the onlyconstexprvariables at namespace scope in that file. The other constants there are function-local or static members. This declares the two constantsJSON_INLINE_VARIABLE constexpr, which the library already uses forstatic_const. It expands toinlinefrom C++17 on and to nothing before, so C++11 and C++14 are unchanged.Not verified on MSVC locally. Checked with Apple Clang at C++11, C++17, and C++20 for both headers (
-Wall -Wextra -Werror, dumping floating-point numbers).API impact
No breaking changes. The two constants are in
nlohmann::detail::dtoa_impland keep their values.Written by Claude Code.
🤖 Generated with Claude Code