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/* Copyright (C) 2025 Wildfire Games.
* This file is part of 0 A.D.
*
* 0 A.D. is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*
* 0 A.D. is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with 0 A.D. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef INCLUDED_PS_STRINGBUILDER
#define INCLUDED_PS_STRINGBUILDER
#include <charconv>
#include <cstdint>
#include <span>
#include <string>
#include <string_view>
#include <type_traits>
#include <version>
#if defined(__cpp_lib_to_chars)
#include <charconv>
#else
#include <fmt/core.h>
#endif
namespace PS
{
/**
* A helper class to build string in-place without additional cost of
* allocations, locales and format parsing. Prefer to use the class with stack
* allocated buffers over standard tools in high-load cases.
* TODO: in case of overflow it might use a heap allocated storage.
*/
class StringBuilder
{
public:
StringBuilder(std::span<char> buffer) noexcept
: m_Buffer{buffer}, m_BufferBegin{buffer.data()}
{
ENSURE(!m_Buffer.empty());
}
template<typename T>
typename std::enable_if<std::is_arithmetic_v<T>>::type Append(const T value) noexcept
{
ENSURE(m_Buffer.size() > 0);
#if defined(__cpp_lib_to_chars)
const std::to_chars_result result{std::to_chars(m_Buffer.data(), m_Buffer.data() + m_Buffer.size() - 1, value)};
ENSURE(result.ec == std::errc());
m_Buffer = m_Buffer.subspan(result.ptr - m_Buffer.data());
// to_chars doesn't write terminating null.
m_Buffer.front() = 0;
#else
// TODO: switch to std::to_chars after minimal libcxx supports it.
const fmt::format_to_n_result result{
fmt::format_to_n(m_Buffer.data(), m_Buffer.size() - 1, "{}", value)};
ENSURE(m_Buffer.data() != result.out);
m_Buffer = m_Buffer.subspan(result.size);
// format_to_n doesn't write terminating null.
m_Buffer.front() = 0;
#endif
}
void Append(const char ch)
{
ENSURE(m_Buffer.size() > 1);
m_Buffer.front() = ch;
m_Buffer = m_Buffer.subspan(1);
m_Buffer.front() = 0;
}
void Append(const std::string_view str) noexcept
{
ENSURE(m_Buffer.size() >= static_cast<size_t>(str.size()) + 1);
std::copy(str.begin(), str.end(), m_Buffer.begin());
m_Buffer = m_Buffer.subspan(str.size());
m_Buffer.front() = 0;
}
/**
* Returns a string_view to a null-terminated string.
*/
std::string_view Str() noexcept
{
return {m_BufferBegin, m_Buffer.data()};
}
private:
std::span<char> m_Buffer;
char* m_BufferBegin;
};
} // namespace PS
#endif // INCLUDED_PS_STRINGBUILDER
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