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<format>: Reserve some space in result string #1803

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Merged
StephanTLavavej merged 5 commits into from
Apr 22, 2021
Merged

<format>: Reserve some space in result string #1803

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c078286
Reserve space in formatted string
AdamBucior Apr 5, 2021
8ccf924
Make it a member function
AdamBucior Apr 5, 2021
6d0b529
Rename to _Estimate_required_capacity
AdamBucior Apr 6, 2021
bd1ecdb
Eliminate strlen
AdamBucior Apr 7, 2021
7380cbb
Add comments explaining magic numbers.
StephanTLavavej Apr 20, 2021
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22 changes: 22 additions & 0 deletions stl/inc/format
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Original file line number Diff line number Diff line change
Expand Up @@ -1451,6 +1451,24 @@ public:
}
}

_NODISCARD size_t _Estimate_required_capacity() const noexcept {
using _CharT = typename _Context::char_type;
size_t _Result = 0;
const auto _Visitor = [&_Result]<class _ArgTy>(const _ArgTy _Arg) noexcept {
if constexpr (is_same_v<_ArgTy, basic_string_view<_CharT>>) {
_Result += _Arg.size();
} else if constexpr (is_same_v<_ArgTy, const _CharT*>) {
_Result += 32; // estimate for length of null-terminated strings
} else {
_Result += 8; // estimate for length of all other arguments
}
};
for (size_t _Idx = 0; _Idx < _Num_args; ++_Idx) {
_STD visit_format_arg(_Visitor, get(_Idx));
}
return _Result;
}

private:
size_t _Num_args = 0;
const unsigned char* _Storage = nullptr;
Expand Down Expand Up @@ -2637,24 +2655,28 @@ _OutputIt format_to(_OutputIt _Out, const locale& _Loc, const wstring_view _Fmt,

_NODISCARD inline string vformat(const string_view _Fmt, const format_args _Args) {
string _Str;
_Str.reserve(_Fmt.size() + _Args._Estimate_required_capacity());
_STD vformat_to(_STD back_inserter(_Str), _Fmt, _Args);
return _Str;
}

_NODISCARD inline wstring vformat(const wstring_view _Fmt, const wformat_args _Args) {
wstring _Str;
_Str.reserve(_Fmt.size() + _Args._Estimate_required_capacity());
_STD vformat_to(_STD back_inserter(_Str), _Fmt, _Args);
return _Str;
}

_NODISCARD inline string vformat(const locale& _Loc, const string_view _Fmt, const format_args _Args) {
string _Str;
_Str.reserve(_Fmt.size() + _Args._Estimate_required_capacity());
_STD vformat_to(_STD back_inserter(_Str), _Loc, _Fmt, _Args);
return _Str;
}

_NODISCARD inline wstring vformat(const locale& _Loc, const wstring_view _Fmt, const wformat_args _Args) {
wstring _Str;
_Str.reserve(_Fmt.size() + _Args._Estimate_required_capacity());
_STD vformat_to(_STD back_inserter(_Str), _Loc, _Fmt, _Args);
return _Str;
}
Expand Down