refactor: refactor encoding helper again.

- add the convertion between yycc_char8_t and system char type because we decide use our char8_t in the whole library.
- make a clear boundary between yycc char8_t declarations and related assist functions. the declarations present in internal header and assist functions are written in encoding helper.
- use std::basic_string_view instead of std::basic_string to provide more abilities to encoding convertion functions and reduce the redundant memory occupation at the same time.

src/EncodingHelper.cpp

@@ -4,88 +4,224 @@
 
 namespace YYCC::EncodingHelper {
 
+#pragma region UTF8 Native Convertion
+	
+	const yycc_char8_t* ToUTF8(const char* src) {
+		return reinterpret_cast<const yycc_char8_t*>(src);
+	}
+	yycc_char8_t* ToUTF8(char* src) {
+		return reinterpret_cast<yycc_char8_t*>(src);
+	}
+	yycc_u8string ToUTF8(const std::string_view& src) {
+		return yycc_u8string(reinterpret_cast<const yycc_char8_t*>(src.data()), src.size());
+	}
+	yycc_u8string_view ToUTF8View(const std::string_view& src) {
+		return yycc_u8string_view(reinterpret_cast<const yycc_char8_t*>(src.data()), src.size());
+	}
+	
+	const char* ToNative(const yycc_char8_t* src) {
+		return reinterpret_cast<const char*>(src);
+	}
+	char* ToNative(yycc_char8_t* src) {
+		return reinterpret_cast<char*>(src);
+	}
+	std::string ToNative(const yycc_u8string_view& src) {
+		return std::string(reinterpret_cast<const char*>(src.data()), src.size());
+	}
+	std::string_view ToNativeView(const yycc_u8string_view& src) {
+		return std::string_view(reinterpret_cast<const char*>(src.data()), src.size());
+	}
+
+#pragma endregion
+
+	/* Define some assistant macros for easy writing. */
+
+#define CONVFCT_TYPE2(fct_name, src_char_type, dst_char_type, ...) if (src == nullptr) return false; \
+std::basic_string_view<src_char_type> cache(src); \
+return fct_name(cache, dst, ##__VA_ARGS__);
+
+#define CONVFCT_TYPE3(fct_name, src_char_type, dst_char_type, ...) std::basic_string<dst_char_type> ret; \
+if (!fct_name(src, ret, ##__VA_ARGS__)) ret.clear(); \
+return ret;
+	
+#define CONVFCT_TYPE4(fct_name, src_char_type, dst_char_type, ...) std::basic_string<dst_char_type> ret; \
+if (!fct_name(src, ret, ##__VA_ARGS__)) ret.clear(); \
+return ret;
+
+
 #if YYCC_OS == YYCC_OS_WINDOWS
 
-	bool WcharToChar(const wchar_t* src, std::string& dest, UINT codepage) {
-		int count, write_result;
+#pragma region WcharToChar
 	
-		//converter to CHAR
-		count = WideCharToMultiByte(codepage, 0, reinterpret_cast<LPCWCH>(src), -1, NULL, 0, NULL, NULL);
-		if (count <= 0) return false;
+	bool WcharToChar(const std::wstring_view& src, std::string& dst, UINT code_page) {
+		// if src is empty, direct output
+		if (src.empty()) {
+			dst.clear();
+			return true;
+		}
 
-		dest.resize(count - 1);
-		write_result = WideCharToMultiByte(codepage, 0, reinterpret_cast<LPCWCH>(src), -1, reinterpret_cast<LPSTR>(dest.data()), count, NULL, NULL);
+		// init WideCharToMultiByte used variables
+		// setup src pointer
+		LPCWCH lpWideCharStr =  reinterpret_cast<LPCWCH>(src.data());
+		// check whether source string is too large.
+		size_t cSrcSize = src.size();
+		if (cSrcSize > std::numeric_limits<int>::max()) return false;
+		int cchWideChar = static_cast<int>(src.size());
+
+		// do convertion
+		// do a dry-run first to fetch desired size.
+		int desired_size = WideCharToMultiByte(code_page, 0, lpWideCharStr, cchWideChar, NULL, 0, NULL, NULL);
+		if (desired_size <= 0) return false;
+		// resize dest for receiving result
+		dst.resize(static_cast<size_t>(desired_size));
+		// do real convertion
+		int write_result = WideCharToMultiByte(code_page, 0, lpWideCharStr, cchWideChar, reinterpret_cast<LPSTR>(dst.data()), desired_size, NULL, NULL);
 		if (write_result <= 0) return false;
 
 		return true;
 	}
-	bool WcharToUTF8(const wchar_t* src, std::string& dest) {
-		return WcharToChar(src, dest, CP_UTF8);
+	bool WcharToChar(const wchar_t* src, std::string& dst, UINT code_page) {
+		CONVFCT_TYPE2(WcharToChar, wchar_t, char, code_page);
 	}
-	std::string WcharToChar(const wchar_t* src, UINT codepage) {
-		std::string ret;
-		if (!WcharToChar(src, ret, codepage)) ret.clear();
-		return ret;
+	std::string WcharToChar(const std::wstring_view& src, UINT code_page) {
+		CONVFCT_TYPE3(WcharToChar, wchar_t, char, code_page);
 	}
-	std::string WcharToUTF8(const wchar_t* src) {
-		return WcharToChar(src, CP_UTF8);
+	std::string WcharToChar(const wchar_t* src, UINT code_page) {
+		CONVFCT_TYPE4(WcharToChar, wchar_t, char, code_page);
 	}
 
-	bool CharToWchar(const char* src, std::wstring& dest, UINT codepage) {
-		int wcount, write_result;
+#pragma endregion
 	
-		// convert to WCHAR
-		wcount = MultiByteToWideChar(codepage, 0, reinterpret_cast<LPCCH>(src), -1, NULL, 0);
-		if (wcount <= 0) return false;
+#pragma region CharToWchar
 
-		dest.resize(wcount - 1);
-		write_result = MultiByteToWideChar(codepage, 0, reinterpret_cast<LPCCH>(src), -1, reinterpret_cast<LPWSTR>(dest.data()), wcount);
+	bool CharToWchar(const std::string_view& src, std::wstring& dst, UINT code_page) {
+		// if src is empty, direct output
+		if (src.empty()) {
+			dst.clear();
+			return true;
+		}
+
+		// init WideCharToMultiByte used variables
+		// setup src pointer
+		LPCCH lpMultiByteStr = reinterpret_cast<LPCCH>(src.data());
+		// check whether source string is too large.
+		size_t cSrcSize = src.size();
+		if (cSrcSize > std::numeric_limits<int>::max()) return false;
+		int cbMultiByte = static_cast<int>(src.size());
+		
+		// do convertion
+		// do a dry-run first to fetch desired size.
+		int desired_size = MultiByteToWideChar(code_page, 0, lpMultiByteStr, cbMultiByte, NULL, 0);
+		if (desired_size <= 0) return false;
+		// resize dest for receiving result
+		dst.resize(static_cast<size_t>(desired_size));
+		// do real convertion
+		int write_result = MultiByteToWideChar(code_page, 0, lpMultiByteStr, cbMultiByte, reinterpret_cast<LPWSTR>(dst.data()), desired_size);
 		if (write_result <= 0) return false;
 
 		return true;
 	}
-	bool UTF8ToWchar(const char* src, std::wstring& dest) {
-		return CharToWchar(src, dest, CP_UTF8);
+	bool CharToWchar(const char* src, std::wstring& dst, UINT code_page) {
+		CONVFCT_TYPE2(CharToWchar, char, wchar_t, code_page);
 	}
-	std::wstring CharToWchar(const char* src, UINT codepage) {
-		std::wstring ret;
-		if (!CharToWchar(src, ret, codepage)) ret.clear();
-		return ret;
+	std::wstring CharToWchar(const std::string_view& src, UINT code_page) {
+		CONVFCT_TYPE3(CharToWchar, char, wchar_t, code_page);
 	}
-	std::wstring UTF8ToWchar(const char* src) {
-		return CharToWchar(src, CP_UTF8);
+	std::wstring CharToWchar(const char* src, UINT code_page) {
+		CONVFCT_TYPE4(CharToWchar, char, wchar_t, code_page);
 	}
 
-	bool CharToChar(const char* src, std::string& dest, UINT src_codepage, UINT dest_codepage) {
+#pragma endregion
+
+#pragma region CharToChar
+	
+	bool CharToChar(const std::string_view& src, std::string& dst, UINT src_code_page, UINT dst_code_page) {
 		std::wstring intermediary;
-		if (!CharToWchar(src, intermediary, src_codepage)) return false;
-		if (!WcharToChar(intermediary.c_str(), dest, dest_codepage)) return false;
+		if (!CharToWchar(src, intermediary, src_code_page)) return false;
+		if (!WcharToChar(intermediary, dst, dst_code_page)) return false;
 		return true;
 	}
-	std::string CharToChar(const char* src, UINT src_codepage, UINT dest_codepage) {
-		std::string ret;
-		if (!CharToChar(src, ret, src_codepage, dest_codepage)) ret.clear();
+	bool CharToChar(const char* src, std::string& dst, UINT src_code_page, UINT dst_code_page) {
+		CONVFCT_TYPE2(CharToChar, char, char, src_code_page, dst_code_page);
+	}
+	std::string CharToChar(const std::string_view& src, UINT src_code_page, UINT dst_code_page) {
+		CONVFCT_TYPE3(CharToChar, char, char, src_code_page, dst_code_page);
+	}
+	std::string CharToChar(const char* src, UINT src_code_page, UINT dst_code_page) {
+		CONVFCT_TYPE4(CharToChar, char, char, src_code_page, dst_code_page);
+	}
+
+#pragma endregion
+
+#pragma region WcharToUTF8
+	
+	bool WcharToUTF8(const std::wstring_view& src, yycc_u8string& dst) {
+		std::string adapted_dst;
+		bool ret = WcharToChar(src, adapted_dst, CP_UTF8);
+		if (ret) dst = ToUTF8(adapted_dst);
 		return ret;
 	}
+	bool WcharToUTF8(const wchar_t* src, yycc_u8string& dst) {
+		CONVFCT_TYPE2(WcharToUTF8, wchar_t, yycc_char8_t);
+	}
+	yycc_u8string WcharToUTF8(const std::wstring_view& src) {
+		CONVFCT_TYPE3(WcharToUTF8, wchar_t, yycc_char8_t);
+	}
+	yycc_u8string WcharToUTF8(const wchar_t* src) {
+		CONVFCT_TYPE4(WcharToUTF8, wchar_t, yycc_char8_t);
+	}
+
+#pragma endregion
+
+#pragma region UTF8ToWchar
+	
+	bool UTF8ToWchar(const yycc_u8string_view& src, std::wstring& dst) {
+		std::string_view adapted_src(ToNativeView(src));
+		return CharToWchar(adapted_src, dst, CP_UTF8);
+	}
+	bool UTF8ToWchar(const yycc_char8_t* src, std::wstring& dst) {
+		CONVFCT_TYPE2(UTF8ToWchar, yycc_char8_t, wchar_t);
+	}
+	std::wstring UTF8ToWchar(const yycc_u8string_view& src) {
+		CONVFCT_TYPE3(UTF8ToWchar, yycc_char8_t, wchar_t);
+	}
+	std::wstring UTF8ToWchar(const yycc_char8_t* src) {
+		CONVFCT_TYPE4(UTF8ToWchar, yycc_char8_t, wchar_t);
+	}
+
+#pragma endregion
 	
 #endif
 
+	
+#pragma region UTF8 UTF16 UTF32 Help Funcs
+
+	/*
+	According to the documentation introduced in CppReference.
+	The standard library is guaranteed to provide several specific specializations of \c std::codecvt.
+	The UTF8 char type in UTF8 related specializations of \c std::codecvt is different.
+	It is also independend from we defined \c yycc_char8_t.
+	So it is essential define a type which can correctly trigger specific specializations of \c std::codecv in there.
+	*/
 #if defined(__cpp_char8_t)
 	using CodecvtUTF8Char_t = char8_t;
 #else
 	using CodecvtUTF8Char_t = char;
 #endif
+
 	template<typename _TChar, std::enable_if_t<std::is_same_v<_TChar, char16_t> || std::is_same_v<_TChar, char32_t>, int> = 0>
 	using CodecvtFacet_t = std::codecvt<_TChar, CodecvtUTF8Char_t, std::mbstate_t>;
 
 	template<typename _TChar, std::enable_if_t<std::is_same_v<_TChar, char16_t> || std::is_same_v<_TChar, char32_t>, int> = 0>
-	static bool UTF8ToUTFOther(const char* _src, std::basic_string<_TChar>& dest) {
+	static bool UTF8ToUTFOther(const yycc_u8string_view& src, std::basic_string<_TChar>& dst) {
 		// Reference:
 		// https://zh.cppreference.com/w/cpp/locale/codecvt/in
 		
-		// init src string
-		if (_src == nullptr) return false;
-		std::string src(_src);
+		// if src is empty, return directly
+		if (src.empty()) {
+			dst.clear();
+			return true;
+		}
 
 		// init locale and get codecvt facet
 		// same reason in UTFOtherToUTF8 to keeping reference to locale
@@ -94,12 +230,12 @@ namespace YYCC::EncodingHelper {
 		
 		// convertion preparation
 		std::mbstate_t mb{};
-		dest.resize(src.size());
-		const CodecvtUTF8Char_t* intern_from = reinterpret_cast<const CodecvtUTF8Char_t*>(src.c_str()),
-			*intern_from_end = reinterpret_cast<const CodecvtUTF8Char_t*>(src.c_str() + src.size()),
+		dst.resize(src.size());
+		const CodecvtUTF8Char_t* intern_from = reinterpret_cast<const CodecvtUTF8Char_t*>(src.data()),
+			*intern_from_end = reinterpret_cast<const CodecvtUTF8Char_t*>(src.data() + src.size()),
 			*intern_from_next = nullptr;
-		_TChar* extern_to = dest.data(),
-			*extern_to_end = dest.data() + dest.size(),
+		_TChar* extern_to = dst.data(),
+			*extern_to_end = dst.data() + dst.size(),
 			*extern_to_next = nullptr;
 		// do convertion
 		auto result = this_codecvt.in(
@@ -112,35 +248,20 @@ namespace YYCC::EncodingHelper {
 		if (result != CodecvtFacet_t<_TChar>::ok)
 			return false;
 		// resize result and return
-		dest.resize(extern_to_next - dest.data());
+		dst.resize(extern_to_next - dst.data());
 		return true;
 	}
 
-	bool UTF8ToUTF16(const char* src, std::u16string& dest) {
-		return UTF8ToUTFOther<char16_t>(src, dest);
-	}
-	std::u16string UTF8ToUTF16(const char* src) {
-		std::u16string ret;
-		if (!UTF8ToUTF16(src, ret)) ret.clear();
-		return ret;
-	}
-	bool UTF8ToUTF32(const char* src, std::u32string& dest) {
-		return UTF8ToUTFOther<char32_t>(src, dest);
-	}
-	std::u32string UTF8ToUTF32(const char* src) {
-		std::u32string ret;
-		if (!UTF8ToUTF32(src, ret)) ret.clear();
-		return ret;
-	}
-
 	template<typename _TChar, std::enable_if_t<std::is_same_v<_TChar, char16_t> || std::is_same_v<_TChar, char32_t>, int> = 0>
-	static bool UTFOtherToUTF8(const _TChar* _src, std::string& dest) {
+	static bool UTFOtherToUTF8(const std::basic_string_view<_TChar>& src, yycc_u8string& dst) {
 		// Reference:
 		// https://zh.cppreference.com/w/cpp/locale/codecvt/out
 		
-		// initialize src string
-		if (_src == nullptr) return false;
-		std::basic_string<_TChar> src(_src);
+		// if src is empty, return directly
+		if (src.empty()) {
+			dst.clear();
+			return true;
+		}
 
 		// init locale and get codecvt facet
 		// the reference to locale must be preserved until convertion done.
@@ -150,12 +271,12 @@ namespace YYCC::EncodingHelper {
 
 		// do convertion preparation
 		std::mbstate_t mb{};
-		dest.resize(src.size() * this_codecvt.max_length());
-		const _TChar* intern_from = src.c_str(),
-			*intern_from_end = src.c_str() + src.size(),
+		dst.resize(src.size() * this_codecvt.max_length());
+		const _TChar* intern_from = src.data(),
+			*intern_from_end = src.data() + src.size(),
 			*intern_from_next = nullptr;
-		CodecvtUTF8Char_t* extern_to = reinterpret_cast<CodecvtUTF8Char_t*>(dest.data()),
-			*extern_to_end = reinterpret_cast<CodecvtUTF8Char_t*>(dest.data() + dest.size()),
+		CodecvtUTF8Char_t* extern_to = reinterpret_cast<CodecvtUTF8Char_t*>(dst.data()),
+			*extern_to_end = reinterpret_cast<CodecvtUTF8Char_t*>(dst.data() + dst.size()),
 			*extern_to_next = nullptr;
 		// do convertion
 		auto result = this_codecvt.out(
@@ -168,26 +289,83 @@ namespace YYCC::EncodingHelper {
 		if (result != CodecvtFacet_t<_TChar>::ok)
 			return false;
 		// resize result and retuen
-		dest.resize(extern_to_next - reinterpret_cast<CodecvtUTF8Char_t*>(dest.data()));
+		dst.resize(extern_to_next - reinterpret_cast<CodecvtUTF8Char_t*>(dst.data()));
 		return true;
 	}
 
-	bool UTF16ToUTF8(const char16_t* src, std::string& dest) {
-		return UTFOtherToUTF8<char16_t>(src, dest);
+#pragma endregion
+
+#pragma region UTF8ToUTF16
+	
+	bool UTF8ToUTF16(const yycc_u8string_view& src, std::u16string& dst) {
+		return UTF8ToUTFOther<char16_t>(src, dst);
 	}
-	std::string UTF16ToUTF8(const char16_t* src) {
-		std::string ret;
-		if (!UTF16ToUTF8(src, ret)) ret.clear();
-		return ret;
+	bool UTF8ToUTF16(const yycc_char8_t* src, std::u16string& dst) {
+		CONVFCT_TYPE2(UTF8ToUTF16, yycc_char8_t, char16_t);
 	}
-	bool UTF32ToUTF8(const char32_t* src, std::string& dest) {
-		return UTFOtherToUTF8<char32_t>(src, dest);
+	std::u16string UTF8ToUTF16(const yycc_u8string_view& src) {
+		CONVFCT_TYPE3(UTF8ToUTF16, yycc_char8_t, char16_t);
 	}
-	std::string UTF32ToUTF8(const char32_t* src) {
-		std::string ret;
-		if (!UTF32ToUTF8(src, ret)) ret.clear();
-		return ret;
+	std::u16string UTF8ToUTF16(const yycc_char8_t* src) {
+		CONVFCT_TYPE4(UTF8ToUTF16, yycc_char8_t, char16_t);
 	}
 
+#pragma endregion
+
+#pragma region UTF16ToUTF8
+	
+	bool UTF16ToUTF8(const std::u16string_view& src, yycc_u8string& dst) {
+		return UTFOtherToUTF8<char16_t>(src, dst);
+	}
+	bool UTF16ToUTF8(const char16_t* src, yycc_u8string& dst) {
+		CONVFCT_TYPE2(UTF16ToUTF8, char16_t, yycc_char8_t);
+	}
+	yycc_u8string UTF16ToUTF8(const std::u16string_view& src) {
+		CONVFCT_TYPE3(UTF16ToUTF8, char16_t, yycc_char8_t);
+	}
+	yycc_u8string UTF16ToUTF8(const char16_t* src) {
+		CONVFCT_TYPE4(UTF16ToUTF8, char16_t, yycc_char8_t);
+	}
+
+#pragma endregion
+	
+#pragma region UTF8ToUTF32
+	
+	bool UTF8ToUTF32(const yycc_u8string_view& src, std::u32string& dst) {
+		return UTF8ToUTFOther<char32_t>(src, dst);
+	}
+	bool UTF8ToUTF32(const yycc_char8_t* src, std::u32string& dst) {
+		CONVFCT_TYPE2(UTF8ToUTF32, yycc_char8_t, char32_t);
+	}
+	std::u32string UTF8ToUTF32(const yycc_u8string_view& src) {
+		CONVFCT_TYPE3(UTF8ToUTF32, yycc_char8_t, char32_t);
+	}
+	std::u32string UTF8ToUTF32(const yycc_char8_t* src) {
+		CONVFCT_TYPE4(UTF8ToUTF32, yycc_char8_t, char32_t);
+	}
+
+#pragma endregion
+
+#pragma region UTF32ToUTF8
+	
+	bool UTF32ToUTF8(const std::u32string_view& src, yycc_u8string& dst) {
+		return UTFOtherToUTF8<char32_t>(src, dst);
+	}
+	bool UTF32ToUTF8(const char32_t* src, yycc_u8string& dst) {
+		CONVFCT_TYPE2(UTF32ToUTF8, char32_t, yycc_char8_t);
+	}
+	yycc_u8string UTF32ToUTF8(const std::u32string_view& src) {
+		CONVFCT_TYPE3(UTF32ToUTF8, char32_t, yycc_char8_t);
+	}
+	yycc_u8string UTF32ToUTF8(const char32_t* src) {
+		CONVFCT_TYPE4(UTF32ToUTF8, char32_t, yycc_char8_t);
+	}
+
+#pragma endregion
+
+#undef CONVFCT_TYPE2
+#undef CONVFCT_TYPE3
+#undef CONVFCT_TYPE4
+
 }
 

src/EncodingHelper.hpp

@@ -50,31 +50,67 @@
 */
 namespace YYCC::EncodingHelper {
 
+#define YYCC_U8(strl) (reinterpret_cast<const yycc_char8_t*>(u8 ## strl))
+
+	const yycc_char8_t* ToUTF8(const char* src);
+	yycc_char8_t* ToUTF8(char* src);
+	yycc_u8string ToUTF8(const std::string_view& src);
+	yycc_u8string_view ToUTF8View(const std::string_view& src);
+
+	const char* ToNative(const yycc_char8_t* src);
+	char* ToNative(yycc_char8_t* src);
+	std::string ToNative(const yycc_u8string_view& src);
+	std::string_view ToNativeView(const yycc_u8string_view& src);
+
 #if YYCC_OS == YYCC_OS_WINDOWS
 
-	bool WcharToChar(const wchar_t* src, std::string& dest, UINT codepage);
-	bool WcharToUTF8(const wchar_t* src, std::string& dest);
-	std::string WcharToChar(const wchar_t* src, UINT codepage);
-	std::string WcharToUTF8(const wchar_t* src);
+	bool WcharToChar(const std::wstring_view& src, std::string& dst, UINT code_page);
+	bool WcharToChar(const wchar_t* src, std::string& dst, UINT code_page);
+	std::string WcharToChar(const std::wstring_view& src, UINT code_page);
+	std::string WcharToChar(const wchar_t* src, UINT code_page);
 
-	bool CharToWchar(const char* src, std::wstring& dest, UINT codepage);
-	bool UTF8ToWchar(const char* src, std::wstring& dest);
-	std::wstring CharToWchar(const char* src, UINT codepage);
-	std::wstring UTF8ToWchar(const char* src);
+	bool CharToWchar(const std::string_view& src, std::wstring& dst, UINT code_page);
+	bool CharToWchar(const char* src, std::wstring& dst, UINT code_page);
+	std::wstring CharToWchar(const std::string_view& src, UINT code_page);
+	std::wstring CharToWchar(const char* src, UINT code_page);
 
-	bool CharToChar(const char* src, std::string& dest, UINT src_codepage, UINT dest_codepage);
-	std::string CharToChar(const char* src, UINT src_codepage, UINT dest_codepage);
+	bool CharToChar(const std::string_view& src, std::string& dst, UINT src_code_page, UINT dst_code_page);
+	bool CharToChar(const char* src, std::string& dst, UINT src_code_page, UINT dst_code_page);
+	std::string CharToChar(const std::string_view& src, UINT src_code_page, UINT dst_code_page);
+	std::string CharToChar(const char* src, UINT src_code_page, UINT dst_code_page);
+
+
+	bool WcharToUTF8(const std::wstring_view& src, yycc_u8string& dst);
+	bool WcharToUTF8(const wchar_t* src, yycc_u8string& dst);
+	yycc_u8string WcharToUTF8(const std::wstring_view& src);
+	yycc_u8string WcharToUTF8(const wchar_t* src);
+
+	bool UTF8ToWchar(const yycc_u8string_view& src, std::wstring& dst);
+	bool UTF8ToWchar(const yycc_char8_t* src, std::wstring& dst);
+	std::wstring UTF8ToWchar(const yycc_u8string_view& src);
+	std::wstring UTF8ToWchar(const yycc_char8_t* src);
 
 #endif
 
-	bool UTF8ToUTF16(const char* src, std::u16string& dest);
-	std::u16string UTF8ToUTF16(const char* src);
-	bool UTF8ToUTF32(const char* src, std::u32string& dest);
-	std::u32string UTF8ToUTF32(const char* src);
+	bool UTF8ToUTF16(const yycc_u8string_view& src, std::u16string& dst);
+	bool UTF8ToUTF16(const yycc_char8_t* src, std::u16string& dst);
+	std::u16string UTF8ToUTF16(const yycc_u8string_view& src);
+	std::u16string UTF8ToUTF16(const yycc_char8_t* src);
 
-	bool UTF16ToUTF8(const char16_t* src, std::string& dest);
-	std::string  UTF16ToUTF8(const char16_t* src);
-	bool UTF32ToUTF8(const char32_t* src, std::string& dest);
-	std::string  UTF32ToUTF8(const char32_t* src);
+	bool UTF16ToUTF8(const std::u16string_view& src, yycc_u8string& dst);
+	bool UTF16ToUTF8(const char16_t* src, yycc_u8string& dst);
+	yycc_u8string UTF16ToUTF8(const std::u16string_view& src);
+	yycc_u8string UTF16ToUTF8(const char16_t* src);
+
+
+	bool UTF8ToUTF32(const yycc_u8string_view& src, std::u32string& dst);
+	bool UTF8ToUTF32(const yycc_char8_t* src, std::u32string& dst);
+	std::u32string UTF8ToUTF32(const yycc_u8string_view& src);
+	std::u32string UTF8ToUTF32(const yycc_char8_t* src);
+
+	bool UTF32ToUTF8(const std::u32string_view& src, yycc_u8string& dst);
+	bool UTF32ToUTF8(const char32_t* src, yycc_u8string& dst);
+	yycc_u8string UTF32ToUTF8(const std::u32string_view& src);
+	yycc_u8string UTF32ToUTF8(const char32_t* src);
 
 }

src/YYCCInternal.hpp

@@ -24,14 +24,20 @@
 
 #endif
 
-//// Decide the char type we used
-//#include <string>
-//namespace YYCC {
-//#if defined(__cpp_char8_t)
-//	using u8char = char8_t;
-//	using u8string = std::std::string
-//#else
-//	using u8char = char;
-//	using u8string = std::string;
-//#endif
-//}
+// Define the UTF8 char type we used.
+// And do a polyfill if no embedded char8_t type.
+#include <string>
+#include <string_view>
+namespace YYCC {
+#if defined(__cpp_char8_t)
+	using yycc_char8_t = char8_t;
+	using yycc_u8string = std::u8string;
+	using yycc_u8string_view = std::u8string_view;
+#else
+	using yycc_char8_t = unsigned char;
+	using yycc_u8string = std::basic_string<yycc_char8_t>;
+	using yycc_u8string_view = std::basic_string_view<yycc_char8_t>;
+#endif
+	
+}
+