C++ string_view类代码示例

void
write_buffer(DynamicBuffer& b, string_view s)
{
    b.commit(boost::asio::buffer_copy(
        b.prepare(s.size()), boost::asio::buffer(
            s.data(), s.size())));
}

int main()
{
    using string_view    = std::experimental::string_view;
    using u16string_view = std::experimental::u16string_view;
    using u32string_view = std::experimental::u32string_view;
    using wstring_view   = std::experimental::wstring_view;

    test(string_view   {});
    test(string_view   { "123"});
    test(u16string_view{});
    test(u16string_view{u"123"});
    test(u32string_view{});
    test(u32string_view{U"123"});
    test(wstring_view  {});
    test(wstring_view  {L"123"});

    {
    constexpr string_view       sv { "123", 3 };
    constexpr u16string_view u16sv {u"123", 3 };
    constexpr u32string_view u32sv {U"123", 3 };
    constexpr wstring_view     wsv {L"123", 3 };
    
    static_assert (    sv.begin() !=    sv.end(), "" );
    static_assert ( u16sv.begin() != u16sv.end(), "" );
    static_assert ( u32sv.begin() != u32sv.end(), "" );
    static_assert (   wsv.begin() !=   wsv.end(), "" );

    static_assert (    sv.begin() !=    sv.cend(), "" );
    static_assert ( u16sv.begin() != u16sv.cend(), "" );
    static_assert ( u32sv.begin() != u32sv.cend(), "" );
    static_assert (   wsv.begin() !=   wsv.cend(), "" );
    }
}

	bdecode_node bdecode_node::dict_find(string_view key) const
	{
		TORRENT_ASSERT(type() == dict_t);

		bdecode_token const* tokens = m_root_tokens;

		// this is the first item
		int token = m_token_idx + 1;

		while (tokens[token].type != bdecode_token::end)
		{
			bdecode_token const& t = tokens[token];
			TORRENT_ASSERT(t.type == bdecode_token::string);
			int const size = m_root_tokens[token + 1].offset - t.offset - t.start_offset();
			if (int(key.size()) == size
				&& std::equal(key.data(), key.data() + size, m_buffer
					+ t.offset + t.start_offset()))
			{
				// skip key
				token += t.next_item;
				TORRENT_ASSERT(tokens[token].type != bdecode_token::end);

				return bdecode_node(tokens, m_buffer, m_buffer_size, token);
			}

			// skip key
			token += t.next_item;
			TORRENT_ASSERT(tokens[token].type != bdecode_token::end);

			// skip value
			token += tokens[token].next_item;
		}

		return bdecode_node();
	}

/// Deconstruct a "URI" string into the "fllename" part (returned) and turn
/// the "query" part into a series of pairs of id and value. For example,
///     deconstruct_uri("foo.tif?bar=1&blah=\"hello world\"", args) 
/// would be expected to return "foo.tif" and *args would contain two
/// pairs: ("foo","1") and ("bar","\"hello world\"").
static string_view
deconstruct_uri (string_view uri,
                 std::vector<std::pair<string_view,string_view> > *args=NULL)
{
    if (args)
        args->clear ();
    size_t arg_start = uri.find ('?');
    if (arg_start == string_view::npos)
        return uri;
    string_view argstring = uri.substr (arg_start+1);
    string_view filename = uri.substr (0, arg_start);
    if (! args)
        return filename;
    while (! argstring.empty()) {
        string_view id = Strutil::parse_until (argstring, "=&");
        string_view value;
        if (! id.size())
            break;
        if (! Strutil::parse_char (argstring, '=') || argstring.empty())
            break;
        if (argstring[0] == '\"')
            Strutil::parse_string (argstring, value, true, Strutil::KeepQuotes);
        else
            value = Strutil::parse_until (argstring, "&\t\r\n");
        args->push_back (std::make_pair(id, value));
        Strutil::parse_char (argstring, '&');
    }
    return filename;
}

//===========================================================================
bool ConsoleReader::onFileRead(
    size_t * bytesRead,
    string_view data,
    bool more,
    int64_t offset,
    FileHandle f
) {
    *bytesRead = data.size();
    auto bytes = (int) data.size();
    socketWrite(&s_socket, move(m_buffer), bytes);

    // stop reading (return false) so we can get a new buffer
    if (m_input) {
        if (m_isFile) {
            if (!bytes || (size_t) offset == fileSize(f)) {
                fileClose(m_input);
                consoleResetStdin();
                init();
            }
        } else {
            if (!bytes) {
                m_buffer.reset();
                return false;
            }
        }
        if (m_suspended) {
            m_offset = offset;
        } else {
            read(offset);
        }
    } else {
        m_buffer.reset();
    }
    return false;
}

	// returns the unicode codepoint and the number of bytes of the utf8 sequence
	// that was parsed. The codepoint is -1 if it's invalid
	std::pair<std::int32_t, int> parse_utf8_codepoint(string_view str)
	{
		int const sequence_len = trailingBytesForUTF8[static_cast<std::uint8_t>(str[0])] + 1;
		if (sequence_len > int(str.size())) return std::make_pair(-1, static_cast<int>(str.size()));

		if (sequence_len > 4)
		{
			return std::make_pair(-1, sequence_len);
		}

		if (!isLegalUTF8(reinterpret_cast<UTF8 const*>(str.data()), sequence_len))
		{
			return std::make_pair(-1, sequence_len);
		}

		std::uint32_t ch = 0;
		for (int i = 0; i < sequence_len; ++i)
		{
			ch <<= 6;
			ch += static_cast<std::uint8_t>(str[static_cast<std::size_t>(i)]);
		}
		ch -= offsetsFromUTF8[sequence_len-1];

		if (ch > 0x7fffffff)
		{
			return std::make_pair(-1, sequence_len);
		}

		return std::make_pair(static_cast<std::int32_t>(ch), sequence_len);
	}

	static bool shouldConsiderUnaryLiteral(string_view& stream, Location& pos)
	{
		// check the previous token
		bool should = (prevType != TokenType::Invalid && prevID == pos.fileID && (
			prevType != TokenType::RParen &&
			prevType != TokenType::RSquare &&
			prevType != TokenType::Identifier &&
			prevType != TokenType::Number &&
			prevType != TokenType::Dollar &&
			prevType != TokenType::StringLiteral
		));

		if(!should) return false;

		// check if the current char is a + or -
		if(stream.length() == 0) return false;
		if(stream[0] != '+' && stream[0] != '-') return false;

		// check if there's only spaces between this and the number itself
		for(size_t i = 1; i < stream.length(); i++)
		{
			if(isdigit(stream[i])) return true;
			else if(stream[i] != ' ') return false;
		}

		return false;
	}

void test_strview_compare(const string_view& a, const string_view& b) {

    std::string as = a.to_string();
    std::string bs = b.to_string();

    auto sg = [](int x) { return x == 0 ? 0 : (x < 0 ? -1 : 1); };
    int c = as.compare(bs);

    ASSERT_EQ(sg(c), sg(a.compare(b)));
    ASSERT_EQ(sg(c), sg(a.compare(bs.c_str())));

    ASSERT_EQ(c == 0, a == b);
    ASSERT_EQ(c != 0, a != b);
    ASSERT_EQ(c <  0, a <  b);
    ASSERT_EQ(c <= 0, a <= b);
    ASSERT_EQ(c >  0, a >  b);
    ASSERT_EQ(c >= 0, a >= b);

    ASSERT_EQ((-c) == 0, b == a);
    ASSERT_EQ((-c) != 0, b != a);
    ASSERT_EQ((-c) <  0, b <  a);
    ASSERT_EQ((-c) <= 0, b <= a);
    ASSERT_EQ((-c) >  0, b >  a);
    ASSERT_EQ((-c) >= 0, b >= a);
}

bool
ColorConfig::reset (string_view filename)
{
    bool ok = true;
    delete m_impl;

    m_impl = new ColorConfig::Impl;
#ifdef USE_OCIO
    OCIO::SetLoggingLevel (OCIO::LOGGING_LEVEL_NONE);
    try {
        if (filename.empty()) {
            getImpl()->config_ = OCIO::GetCurrentConfig();
        } else {
            getImpl()->config_ = OCIO::Config::CreateFromFile (filename.c_str());
        }
    }
    catch(OCIO::Exception &e) {
        getImpl()->error_ = e.what();
        ok = false;
    }
    catch(...) {
        getImpl()->error_ = "An unknown error occurred in OpenColorIO creating the config";
        ok = false;
    }
#endif

    getImpl()->inventory ();

    // If we populated our own, remove any errors.
    if (getNumColorSpaces() && !getImpl()->error_.empty())
        getImpl()->error_.clear();

    return ok;
}

vector<int> readIntegerFile(string_view fileName)
{
	ifstream inputStream(fileName.data());
	if (inputStream.fail()) {
		// We failed to open the file: throw an exception
		const string error = "Unable to open file "s + fileName.data();
		throw invalid_argument(error);
	}

	// Read the integers one-by-one and add them to a vector
	vector<int> integers;
	int temp;
	while (inputStream >> temp) {
		integers.push_back(temp);
	}

	if (!inputStream.eof()) {
		// We did not reach the end-of-file.
		// This means that some error occurred while reading the file.
		// Throw an exception.
		const string error = "Unable to read file "s + fileName.data();
		throw runtime_error(error);
	}

	return integers;
}

void stdLogger(int level, string_view msg) noexcept
{
  const auto now = UnixClock::now();
  const auto t = UnixClock::to_time_t(now);
  const auto ms = timeToMs(now);

  struct tm tm;
  localtime_r(&t, &tm);

  // The following format has an upper-bound of 42 characters:
  // "%b %d %H:%M:%S.%03d %-7s [%d]: "
  //
  // Example:
  // Mar 14 00:00:00.000 WARNING [0123456789]: msg...
  // <---------------------------------------->
  char head[42 + 1];
  size_t hlen = strftime(head, sizeof(head), "%b %d %H:%M:%S", &tm);
  hlen += sprintf(head + hlen, ".%03d %-7s [%d]: ", static_cast<int>(ms % 1000), logLabel(level),
                  static_cast<int>(getpid()));
  char tail = '\n';
  iovec iov[] = {
    {head, hlen}, //
    {const_cast<char*>(msg.data()), msg.size()}, //
    {&tail, 1} //
  };

  int fd{level > LogWarning ? STDOUT_FILENO : STDERR_FILENO};
// Best effort given that this is the logger.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
  writev(fd, iov, sizeof(iov) / sizeof(iov[0]));
#pragma GCC diagnostic pop
}

string transcription::to_rna(string_view strand)
{
    string result;
    transform(strand.begin(), strand.end(), back_inserter(result),
        static_cast<char (*)(char)>(to_rna));
    return result;
}

void Request::add_line_to_multiline_header(const string_view& line,
                                           const string_view& header)
{
    auto non_whitespace_pos = line.find_first_not_of("\t ");
    if (non_whitespace_pos != line.end())
        if (!header.empty())
            headers_[header.str()] += line.substr(non_whitespace_pos).str();
}

Exception::Exception(string_view what) noexcept
{
    const auto len = min(what.size(), MaxErrMsg);
    if (len > 0) {
        memcpy(what_, what.data(), len);
    }
    what_[len] = '\0';
}

// Is name the same as suffix, or does it end in ".suffix"?
inline bool
is_or_endswithdot (string_view name, string_view suffix)
{
    return (Strutil::iequals (name, suffix) ||
            (name.size() > suffix.size() &&
             Strutil::iends_with (name, suffix) &&
             name[name.size()-suffix.size()-1] == '.'));
}