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Appending a space to guarantee non-empty strftime() result. (#2244)

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yumeyao 2021-04-19 10:13:51 +08:00 committed by GitHub
parent 6271406233
commit c5d4fcb119
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1 changed files with 6 additions and 8 deletions
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14
include/fmt/chrono.h
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@ -434,6 +434,10 @@ template <typename Char> struct formatter<std::tm, Char> {
-> decltype(ctx.out()) {
basic_memory_buffer<Char> tm_format;
tm_format.append(specs.begin(), specs.end());
// By appending an extra space we can distinguish an empty result that
// indicates insufficient buffer size from a guaranteed non-empty result
// https://github.com/fmtlib/fmt/issues/2238
tm_format.push_back(' ');
tm_format.push_back('\0');
basic_memory_buffer<Char> buf;
size_t start = buf.size();
@ -444,17 +448,11 @@ template <typename Char> struct formatter<std::tm, Char> {
buf.resize(start + count);
break;
}
if (size >= tm_format.size() * 256) {
// If the buffer is 256 times larger than the format string, assume
// that `strftime` gives an empty result. There doesn't seem to be a
// better way to distinguish the two cases:
// https://github.com/fmtlib/fmt/issues/367
break;
}
const size_t MIN_GROWTH = 10;
buf.reserve(buf.capacity() + (size > MIN_GROWTH ? size : MIN_GROWTH));
}
return std::copy(buf.begin(), buf.end(), ctx.out());
// Remove the extra space.
return std::copy(buf.begin(), buf.end() - 1, ctx.out());
}
basic_string_view<Char> specs;