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Massive speedup to file_equal and file_to_string #1584

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Massive speedup to file_equal and file_to_string #1584

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a794682
Massive speedup to file_equal and file_to_string
DefaultRyan May 22, 2026
e637371
Properly cast the result of tellg() and handle filesystem errors more…
DefaultRyan May 22, 2026
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31 changes: 23 additions & 8 deletions cppwinrt/text_writer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -13,8 +13,26 @@ namespace cppwinrt
{
inline std::string file_to_string(std::string const& filename)
{
std::ifstream file(filename, std::ios::binary);
return static_cast<std::stringstream const&>(std::stringstream() << file.rdbuf()).str();
std::ifstream file(filename, std::ios::binary | std::ios::ate);
if (!file) { return{}; }

const auto stream_size = file.tellg();
if (stream_size == std::ifstream::pos_type(-1))
{
return {};
}

file.seekg(0);

auto size = static_cast<std::size_t>(stream_size);
std::string result(size, '\0');
file.read(result.data(), size);
if (!file)
{
result.resize(static_cast<std::size_t>(file.gcount()));
}

return result;
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}

template <typename T>
Expand Down Expand Up @@ -218,18 +236,15 @@ namespace cppwinrt

bool file_equal(std::string const& filename) const
{
if (!std::filesystem::exists(filename))
// Non-throwing file_size returns uintmax_t(-1) on errors, which shouldn't ever be the size of m_first or m_second
std::error_code ec;
if (std::filesystem::file_size(filename, ec) != m_first.size() + m_second.size())
{
return false;
}

auto file = file_to_string(filename);

if (file.size() != m_first.size() + m_second.size())
{
return false;
}

if (!std::equal(m_first.begin(), m_first.end(), file.begin(), file.begin() + m_first.size()))
{
return false;
Expand Down
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