diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 7bef8bf..e032a90 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -31,6 +31,7 @@ PRIVATE
     yycc/carton/tabulate.cpp
     yycc/carton/ironpad.cpp
     yycc/carton/csconsole.cpp
+    #yycc/carton/clap/option.cpp
 )
 target_sources(YYCCommonplace 
 PUBLIC
@@ -46,6 +47,7 @@ FILES
     yycc/macro/compiler_detector.hpp
     yycc/macro/ptr_size_detector.hpp
     yycc/macro/class_copy_move.hpp
+    yycc/macro/printf_checker.hpp
     yycc/flag_enum.hpp
     yycc/string/reinterpret.hpp
     yycc/string/op.hpp
@@ -81,6 +83,9 @@ FILES
     yycc/carton/tabulate.hpp
     yycc/carton/ironpad.hpp
     yycc/carton/csconsole.hpp
+    yycc/carton/clap.hpp
+    yycc/carton/clap/types.hpp
+    yycc/carton/clap/option.hpp
 )
 # Setup header infomations
 target_include_directories(YYCCommonplace
diff --git a/src/yycc/carton/clap.hpp b/src/yycc/carton/clap.hpp
new file mode 100644
index 0000000..32f766e
--- /dev/null
+++ b/src/yycc/carton/clap.hpp
@@ -0,0 +1,5 @@
+#pragma once
+
+namespace yycc::carton::clap {
+    
+}
diff --git a/src/yycc/carton/clap/option.cpp b/src/yycc/carton/clap/option.cpp
new file mode 100644
index 0000000..0f6f72e
--- /dev/null
+++ b/src/yycc/carton/clap/option.cpp
@@ -0,0 +1,5 @@
+#include "option.hpp"
+
+namespace yycc::carton::clap::option {
+    
+}
diff --git a/src/yycc/carton/clap/option.hpp b/src/yycc/carton/clap/option.hpp
new file mode 100644
index 0000000..bfbde59
--- /dev/null
+++ b/src/yycc/carton/clap/option.hpp
@@ -0,0 +1,85 @@
+#pragma once
+#include "types.hpp"
+#include "../../macro/class_copy_move.hpp"
+#include "../../string/op.hpp"
+#include <optional>
+#include <stdexcept>
+#include <format>
+#include <string>
+
+#define NS_YYCC_CLAP_TYPES ::yycc::carton::clap::types
+
+namespace yycc::carton::clap::option {
+
+    class Option {
+    public:
+        Option(std::optional<std::u8string_view> short_name,
+               std::optional<std::u8string_view> long_name,
+               std::optional<std::u8string_view> value_hint,
+               const std::u8string& description) :
+            short_name(short_name), long_name(long_name), value_hint(value_hint), description(description) {
+            if (!short_name.has_value() && !long_name.has_value()) {
+                throw std::logic_error("must have at least one name, short or long name");
+            }
+
+            if (short_name.has_value()) {
+                const auto& short_name_value = short_name.value();
+                if (!legal_short_name(short_name_value)) {
+                    throw std::logic_error(std::format("invalid short name {}", short_name_value));
+                }
+            }
+            if (long_name.has_value()) {
+                const auto& long_name_value = long_name.value();
+                if (!legal_long_name(long_name_value)) {
+                    throw std::logic_error(std::format("invalid long name {}", long_name_value));
+                }
+            }
+        }
+        ~Option() {}
+        YYCC_DEFAULT_COPY_MOVE(Option)
+
+    public:
+        std::optional<std::u8string_view> get_short_name() const { return this->short_name; }
+        std::optional<std::u8string_view> get_long_name() const { return this->long_name; }
+        std::optional<std::u8string_view> get_value_hint() const { return this->value_hint; }
+        std::u8string_view get_description() const { return this->description; }
+
+        std::u8string to_showcase_name() {
+            namespace op = ::yycc::string::op;
+
+            if (short_name.has_value()) {
+                if (long_name.has_value()) {
+                    
+                } else {
+                
+                }
+            } else {
+                if (long_name.has_value()) {
+                    op::printf
+                } else {
+                    throw std::runtime_error("both long name and short name are empty");
+                }
+            }
+        }
+
+    private:
+        static bool legal_short_name(const std::u8string_view& name) {
+            if (name.empty()) return false;
+            if (name.starts_with(NS_YYCC_CLAP_TYPES::DASH)) return false;
+            return true;
+        }
+        static bool legal_long_name(const std::u8string_view& name) {
+            if (name.empty()) return false;
+            return true;
+        }
+
+    private:
+        std::optional<std::u8string> short_name;
+        std::optional<std::u8string> long_name;
+        std::optional<std::u8string> value_hint;
+        std::u8string description;
+    };
+
+} // namespace yycc::carton::clap::option
+
+#undef NS_YYCC_CLAP_TYPES
diff --git a/src/yycc/carton/clap/types.hpp b/src/yycc/carton/clap/types.hpp
new file mode 100644
index 0000000..0f790d5
--- /dev/null
+++ b/src/yycc/carton/clap/types.hpp
@@ -0,0 +1,19 @@
+#pragma once
+#include <expected>
+#include <string_view>
+
+namespace yycc::carton::clap::types {
+
+    enum class ClapError {
+
+    };
+
+    template<typename T>
+    using ClapResult = std::expected<T, ClapError>;
+
+    inline constexpr std::u8string_view DASH = u8"-";
+    inline constexpr std::u8string_view DOUBLE_DASH = u8"--";
+
+    using Token = size_t;
+
+} // namespace yycc::carton::clap::types
diff --git a/src/yycc/carton/csconsole.cpp b/src/yycc/carton/csconsole.cpp
index f911a10..e3f6c3c 100644
--- a/src/yycc/carton/csconsole.cpp
+++ b/src/yycc/carton/csconsole.cpp
@@ -108,9 +108,7 @@ namespace yycc::carton::csconsole {
         if (GetConsoleMode(hStdOut, &dwConsoleMode)) {
             // console handle, use WriteConsoleW.
             // convert utf8 string to wide char first
-            auto rv = ENC::to_wchar(strl);
-            if (!rv.has_value()) return;
-            std::wstring wstrl(std::move(rv.value()));
+            std::wstring wstrl = ENC::to_wchar(strl).value();
             size_t wstrl_size = wstrl.size();
             // write string with size check
             if (wstrl_size <= std::numeric_limits<DWORD>::max()) {
@@ -171,11 +169,8 @@ namespace yycc::carton::csconsole {
             // treat as format string
             va_list argcpy;
             va_copy(argcpy, argptr);
-            auto rv = OP::vprintf(u8_fmt, argcpy);
+            strl = OP::vprintf(u8_fmt, argcpy);
             va_end(argcpy);
-            // check format result
-            if (!rv.has_value()) return;
-            else strl = std::move(rv.value());
         } else {
             // treat as plain string
             strl = u8_fmt;
diff --git a/src/yycc/carton/ironpad.cpp b/src/yycc/carton/ironpad.cpp
index 3077aca..c9403ec 100644
--- a/src/yycc/carton/ironpad.cpp
+++ b/src/yycc/carton/ironpad.cpp
@@ -63,11 +63,9 @@ namespace yycc::carton::ironpad {
             // check singleton
             // build mutex string first
             auto mutex_name = OP::printf(u8"Global\\%" PRIu32 ".{61634294-d23c-43f9-8490-b5e09837eede}", GetCurrentProcessId());
-            if (!mutex_name.has_value()) return false;
-            auto w_mutex_name = ENC::to_wchar(mutex_name.value());
-            if (!w_mutex_name.has_value()) return false;
+            auto wmutex_name = ENC::to_wchar(mutex_name).value();
             // create mutex
-            m_SingletonMutex = CreateMutexW(NULL, FALSE, w_mutex_name.value().c_str());
+            m_SingletonMutex = CreateMutexW(NULL, FALSE, wmutex_name.c_str());
             DWORD errcode = GetLastError();
             // check whether be created
             if (m_SingletonMutex == NULL) return false;
@@ -303,18 +301,17 @@ namespace yycc::carton::ironpad {
             DWORD process_id = GetCurrentProcessId();
             // conbine them as a file name prefix
             auto u8_filename_prefix = OP::printf(u8"%s.%" PRIu32, u8_process_name.c_str(), process_id);
-            if (!u8_filename_prefix.has_value()) return std::nullopt;
             // then get file name for log and minidump
             std::u8string u8_filename;
             switch (kind) {
                 case FileKind::LogFile:
-                    u8_filename = u8_filename_prefix.value() + u8".log";
+                    u8_filename = u8_filename_prefix + u8".log";
                     break;
                 case FileKind::CoredumpFile:
-                    u8_filename = u8_filename_prefix.value() + u8".dmp";
+                    u8_filename = u8_filename_prefix + u8".dmp";
                     break;
                 default:
-                    u8_filename = u8_filename_prefix.value();
+                    u8_filename = u8_filename_prefix;
                     break;
             }
 
@@ -451,11 +448,9 @@ namespace yycc::carton::ironpad {
          * @details This function will write coredump of given exception into given file path.
          */
         void do_coredump(const std::u8string_view& u8_filename, LPEXCEPTION_POINTERS info) {
-            // convert file encoding
-            // if convertion failed, return
-            auto filename_rv = ENC::to_wchar(u8_filename);
-            if (!filename_rv.has_value()) return;
-            std::wstring filename = filename_rv.value();
+            // convert file encoding.
+            // it must be okey.
+            auto filename = ENC::to_wchar(u8_filename).value();
 
             // open file and write
             HANDLE hFile = CreateFileW(filename.c_str(), GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
@@ -554,15 +549,11 @@ namespace yycc::carton::ironpad {
 	     * @param[in] ... The argument to be formatted.
 	    */
         void log_format_line(std::FILE* fs, const char8_t* fmt, ...) {
-            // do format first
+            // write to file and console
             va_list arg;
             va_start(arg, fmt);
-            auto fmt_rv = OP::vprintf(fmt, arg);
+            log_write_line(fs, OP::vprintf(fmt, arg).c_str());
             va_end(arg);
-            // write to file and console
-            if (fmt_rv.has_value()) {
-                log_write_line(fs, fmt_rv.value().c_str());
-            }
         }
     };
 
diff --git a/src/yycc/carton/wcwidth.cpp b/src/yycc/carton/wcwidth.cpp
index 05188f0..c810d0a 100644
--- a/src/yycc/carton/wcwidth.cpp
+++ b/src/yycc/carton/wcwidth.cpp
@@ -468,11 +468,8 @@ namespace yycc::carton::wcwidth {
     }
 
     Result<size_t> wcswidth(const std::u8string_view& rhs) {
-        // Cast encoding
-        auto u32str = ENC::to_utf32(rhs);
-        if (!u32str.has_value()) return std::unexpected(Error::BadEncoding);
-        // Call underlying function
-        return wcswidth(u32str.value());
+        // Cast encoding and call underlying function
+        return wcswidth(ENC::to_utf32(rhs).value());
     }
 
 } // namespace yycc::carton::wcwidth
diff --git a/src/yycc/carton/wcwidth.hpp b/src/yycc/carton/wcwidth.hpp
index 2b1520c..a879a48 100644
--- a/src/yycc/carton/wcwidth.hpp
+++ b/src/yycc/carton/wcwidth.hpp
@@ -31,7 +31,6 @@ namespace yycc::carton::wcwidth {
 
     /// @brief Error occurs in this module
     enum class Error {
-        BadEncoding,   ///< Given
         BadAnsiEscSeq, ///< Bad char when processing ANSI Escape Sequence
         BadCsiSeq,     ///< Bad char when processing CSI Sequence.
     };
diff --git a/src/yycc/macro/printf_checker.hpp b/src/yycc/macro/printf_checker.hpp
new file mode 100644
index 0000000..7ba7758
--- /dev/null
+++ b/src/yycc/macro/printf_checker.hpp
@@ -0,0 +1,28 @@
+#pragma once
+#include "compiler_detector.hpp"
+#include "stl_detector.hpp"
+
+// YYC MARK:
+// This code is copied from Qt project.
+
+#if defined(YYCC_CC_GCC)
+// GCC has its special attribute
+#define YYCC_PRINTF_CHECK_ATTR(A, B) __attribute__((format(gnu_printf, (A), (B))))
+#elif defined(YYCC_CC_CLANG)
+// Clang use its own attribute
+#define YYCC_PRINTF_CHECK_ATTR(A, B) __attribute__((format(printf, (A), (B))))
+#else
+// Other CC do not support this (like MSVC), skip it
+#define YYCC_PRINTF_CHECK_ATTR(A, B)
+#endif
+
+#if defined(YYCC_STL_MSSTL)
+// On Microsoft STL, we can use some mechanisms to check it.
+#include "../windows/import_guard_head.hpp"
+#include <sal.h>
+#include "../windows/import_guard_tail.hpp"
+#define YYCC_PRINTF_CHECK_FMTSTR _Printf_format_string_
+#else
+// Other STL do not have this.
+#define YYCC_PRINTF_CHECK_FMTSTR
+#endif
diff --git a/src/yycc/patch/fopen.cpp b/src/yycc/patch/fopen.cpp
index 8bf3470..a10cf5d 100644
--- a/src/yycc/patch/fopen.cpp
+++ b/src/yycc/patch/fopen.cpp
@@ -18,19 +18,9 @@ namespace yycc::patch::fopen {
 
     std::FILE* fopen(const char8_t* u8_filepath, const char8_t* u8_mode) {
 #if defined(YYCC_OS_WINDOWS)
-        // convert mode and file path to wchar
-        auto wmode = ENC::to_wchar(u8_mode);
-        auto wpath = ENC::to_wchar(u8_filepath);
-
-        // check convertion success
-        if (wmode.has_value() && wpath.has_value()) {
-            // Call MSVCRT specified fopen which support wchar as argument.
-            // Reference: https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fopen-wfopen?view=msvc-170
-            return _wfopen(wpath.value().c_str(), wmode.value().c_str());
-        } else {
-            // fail to convert encoding
-            return nullptr;
-        }
+        // Convert encoding first, and call MSVCRT specified fopen which support wchar as argument.
+        // Reference: https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fopen-wfopen?view=msvc-170
+        return _wfopen(ENC::to_wchar(u8_filepath).value().c_str(), ENC::to_wchar(u8_mode).value().c_str());
 #else
         return std::fopen(REINTERPRET::as_ordinary(u8_filepath), REINTERPRET::as_ordinary(u8_mode));
 #endif
diff --git a/src/yycc/rust/env.cpp b/src/yycc/rust/env.cpp
index d25247f..65a592d 100644
--- a/src/yycc/rust/env.cpp
+++ b/src/yycc/rust/env.cpp
@@ -25,10 +25,7 @@ namespace yycc::rust::env {
 #if defined(YYCC_OS_WINDOWS)
         // Reference: https://learn.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-getenvironmentvariablew
         // Convert to wchar
-        auto wname = ENC::to_wchar(name);
-        if (!wname.has_value()) {
-            return std::unexpected(EnvError::BadEncoding);
-        }
+        auto wname = ENC::to_wchar(name).value();
 
         // Prepare a variable with proper init size for holding value.
         std::wstring wvalue;
@@ -42,7 +39,7 @@ namespace yycc::rust::env {
             // So we forcely use checked add and sub for this bad behavior.
             auto fct_size = SAFEOP::checked_add<size_t>(wvalue.size(), 1);
             if (!fct_size.has_value()) return std::unexpected(EnvError::BadArithmetic);
-            auto rv = ::GetEnvironmentVariableW(wname.value().c_str(), wvalue.data(), fct_size.value());
+            auto rv = ::GetEnvironmentVariableW(wname.c_str(), wvalue.data(), fct_size.value());
 
             // Check the return value
             if (rv == 0) {
@@ -95,20 +92,10 @@ namespace yycc::rust::env {
 #if defined(YYCC_OS_WINDOWS)
         // Reference: https://learn.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-setenvironmentvariablew
 
-        // Convert to wchar
-        auto wname = ENC::to_wchar(name);
-        auto wvalue = ENC::to_wchar(value);
-        if (!(wname.has_value() && wvalue.has_value())) {
-            return std::unexpected(EnvError::BadEncoding);
-        }
-
-        // Delete variable and check result.
-        auto rv = ::SetEnvironmentVariableW(wname.value().c_str(), wvalue.value().c_str());
-        if (!rv) {
-            return std::unexpected(EnvError::BadCall);
-        }
-
-        return {};
+        // Convert to wchar, set variable, and check result.
+        auto rv = ::SetEnvironmentVariableW(ENC::to_wchar(name).value().c_str(), ENC::to_wchar(value).value().c_str());
+        if (!rv) return std::unexpected(EnvError::BadCall);
+        else return {};
 #else
         // Reference: https://pubs.opengroup.org/onlinepubs/9699919799/functions/setenv.html
 
@@ -129,19 +116,10 @@ namespace yycc::rust::env {
 #if defined(YYCC_OS_WINDOWS)
         // Reference: https://learn.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-setenvironmentvariablew
 
-        // Convert to wchar
-        auto wname = ENC::to_wchar(name);
-        if (!wname.has_value()) {
-            return std::unexpected(EnvError::BadEncoding);
-        }
-
-        // Delete variable and check result.
-        auto rv = ::SetEnvironmentVariableW(wname.value().c_str(), NULL);
-        if (!rv) {
-            return std::unexpected(EnvError::BadCall);
-        }
-
-        return {};
+        // Convert to wchar, delete variable, and check result.
+        auto rv = ::SetEnvironmentVariableW(ENC::to_wchar(name).value().c_str(), NULL);
+        if (!rv) return std::unexpected(EnvError::BadCall);
+        else return {};
 #else
         // Reference: https://pubs.opengroup.org/onlinepubs/9699919799/functions/unsetenv.html
 
diff --git a/src/yycc/string/op.cpp b/src/yycc/string/op.cpp
index 357149e..48efdac 100644
--- a/src/yycc/string/op.cpp
+++ b/src/yycc/string/op.cpp
@@ -1,19 +1,21 @@
 #include "op.hpp"
+#include <type_traits>
 #include <algorithm>
+#include <stdexcept>
 
 namespace yycc::string::op {
 
 #pragma region Printf VPrintf
 
+    /// @brief The concept for all viable char type in printf function family
     template<typename TChar>
-        requires(sizeof(TChar) == sizeof(char))
-    static FormatResult<std::basic_string<TChar>> generic_printf(const TChar* format, va_list argptr) {
+    concept PrintfSupportedChar = std::is_same_v<TChar, char> || std::is_same_v<TChar, char8_t>;
+
+    template<PrintfSupportedChar TChar>
+    static std::basic_string<TChar> generic_printf(const TChar* format, va_list argptr) {
         // Prepare result
         std::basic_string<TChar> rv;
 
-        // Check format
-        if (format == nullptr) return std::unexpected(FormatError::NullFormat);
-
         // Prepare variable arguments
         va_list args1;
         va_copy(args1, argptr);
@@ -21,12 +23,13 @@ namespace yycc::string::op {
         va_copy(args2, argptr);
 
         // The return value is desired char count without NULL terminal.
-        // Minus number means error.
+        // Negative number means error.
         int count = std::vsnprintf(nullptr, 0, reinterpret_cast<const char*>(format), args1);
         // Check expected size.
         if (count < 0) {
             // Invalid length returned by vsnprintf.
-            return std::unexpected(FormatError::NoDesiredSize);
+            // This may be caused by invalid format string
+            throw std::logic_error("fail to determine the size of formatted string");
         }
         va_end(args1);
 
@@ -39,14 +42,15 @@ namespace yycc::string::op {
         // Check written size.
         if (write_result < 0 || write_result > count) {
             // Invalid write result in vsnprintf.
-            return std::unexpected(FormatError::BadWrittenSize);
+            // Idk why this can happen.
+            throw std::logic_error("the size of written formatted string is not expected");
         }
 
         // Return value
         return rv;
     }
 
-    FormatResult<std::u8string> printf(const char8_t* format, ...) {
+    std::u8string printf(const char8_t* format, ...) {
         va_list argptr;
         va_start(argptr, format);
         auto rv = vprintf(format, argptr);
@@ -54,11 +58,11 @@ namespace yycc::string::op {
         return rv;
     }
 
-    FormatResult<std::u8string> vprintf(const char8_t* format, va_list argptr) {
+    std::u8string vprintf(const char8_t* format, va_list argptr) {
         return generic_printf(format, argptr);
     }
 
-    FormatResult<std::string> printf(const char* format, ...) {
+    std::string printf(const char* format, ...) {
         va_list argptr;
         va_start(argptr, format);
         auto rv = vprintf(format, argptr);
@@ -66,7 +70,7 @@ namespace yycc::string::op {
         return rv;
     }
 
-    FormatResult<std::string> vprintf(const char* format, va_list argptr) {
+    std::string vprintf(const char* format, va_list argptr) {
         return generic_printf(format, argptr);
     }
 
diff --git a/src/yycc/string/op.hpp b/src/yycc/string/op.hpp
index 53e37fb..54b6055 100644
--- a/src/yycc/string/op.hpp
+++ b/src/yycc/string/op.hpp
@@ -1,50 +1,41 @@
 #pragma once
+#include "../macro/printf_checker.hpp"
 #include <string>
 #include <string_view>
 #include <cstdarg>
 #include <functional>
 #include <vector>
-#include <expected>
 
 namespace yycc::string::op {
 
-    enum class FormatError {
-        NullFormat,     ///< Given format string is nullptr.
-        NoDesiredSize,  ///< Fail to fetch the expected size of result.
-        BadWrittenSize, ///< The written size is different with expected size.
-    };
-
-    template<typename T>
-    using FormatResult = std::expected<T, FormatError>;
-
     /**
      * @brief Perform an UTF8 string formatting operation.
      * @param[in] format The format string.
      * @param[in] ... Argument list of format string.
-     * @return The formatted result, or the fail reason.
+     * @return The formatted result.
     */
-    FormatResult<std::u8string> printf(const char8_t* format, ...);
+    std::u8string printf(YYCC_PRINTF_CHECK_FMTSTR const char8_t* format, ...) YYCC_PRINTF_CHECK_ATTR(1, 2);
     /**
      * @brief Perform an UTF8 string formatting operation.
      * @param[in] format The format string.
      * @param[in] argptr Argument list of format string.
-     * @return The formatted result, or the fail reason.
+     * @return The formatted result.
     */
-    FormatResult<std::u8string> vprintf(const char8_t* format, va_list argptr);
+    std::u8string vprintf(const char8_t* format, va_list argptr);
     /**
      * @brief Perform an ordinary string formatting operation.
      * @param[in] format The format string.
      * @param[in] ... Argument list of format string.
-     * @return The formatted result, or the fail reason.
+     * @return The formatted result.
     */
-    FormatResult<std::string> printf(const char* format, ...);
+    std::string printf(YYCC_PRINTF_CHECK_FMTSTR const char* format, ...) YYCC_PRINTF_CHECK_ATTR(1, 2);
     /**
      * @brief Perform an ordinary string formatting operation.
      * @param[in] format The format string.
      * @param[in] argptr Argument list of format string.
-     * @return The formatted result, or the fail reason.
+     * @return The formatted result.
     */
-    FormatResult<std::string> vprintf(const char* format, va_list argptr);
+    std::string vprintf(const char* format, va_list argptr);
 
     /**
 	 * @brief Modify given string with all occurrences of substring \e old replaced by \e new.
diff --git a/src/yycc/windows/dialog.cpp b/src/yycc/windows/dialog.cpp
index b9c0a57..2ab219b 100644
--- a/src/yycc/windows/dialog.cpp
+++ b/src/yycc/windows/dialog.cpp
@@ -130,21 +130,15 @@ namespace yycc::windows::dialog {
         // build new Windows oriented string vector
         for (const auto& item : m_Filters) {
             // convert name to wchar
-            auto win_name = ENC::to_wchar(item.first);
-            if (!win_name.has_value()) {
-                return std::unexpected(DialogError::BadEncoding);
-            }
+            auto win_name = ENC::to_wchar(item.first).value();
 
             // join pattern string and convert to wchar
             const auto& modes = item.second;
             auto joined_modes = OP::join(modes.begin(), modes.end(), u8";");
-            auto win_modes = ENC::to_wchar(joined_modes);
-            if (!win_modes.has_value()) {
-                return std::unexpected(DialogError::BadEncoding);
-            }
+            auto win_modes = ENC::to_wchar(joined_modes).value();
 
             // append this pair
-            rv.m_WinFilters.emplace_back(std::make_pair(win_name.value(), win_modes.value()));
+            rv.m_WinFilters.emplace_back(std::make_pair(win_name, win_modes));
         }
 
         // update data struct
@@ -305,28 +299,21 @@ namespace yycc::windows::dialog {
 
         // build title and init file name
         if (m_Title.has_value()) {
-            auto win_title = ENC::to_wchar(m_Title.value());
-            if (!win_title.has_value()) return std::unexpected(DialogError::BadEncoding);
-            else rv.m_WinTitle = win_title.value();
+            rv.m_WinTitle = ENC::to_wchar(m_Title.value()).value();
         } else rv.m_WinTitle = std::nullopt;
         if (m_InitFileName.has_value()) {
-            auto win_init_file_name = ENC::to_wchar(m_InitFileName.value());
-            if (!win_init_file_name.has_value()) return std::unexpected(DialogError::BadEncoding);
-            else rv.m_WinInitFileName = win_init_file_name.value();
+            rv.m_WinInitFileName = ENC::to_wchar(m_InitFileName.value()).value();
         } else rv.m_WinInitFileName = std::nullopt;
 
         // fetch init directory
         if (m_InitDirectory.has_value()) {
             // convert to wchar path
-            auto w_init_dir = ENC::to_wchar(m_InitDirectory.value());
-            if (!w_init_dir.has_value()) {
-                return std::unexpected(DialogError::BadEncoding);
-            }
+            auto w_init_dir = ENC::to_wchar(m_InitDirectory.value()).value();
 
             // fetch IShellItem*
             // Ref: https://stackoverflow.com/questions/76306324/how-to-set-default-folder-for-ifileopendialog-interface
             IShellItem* init_directory = NULL;
-            HRESULT hr = SHCreateItemFromParsingName(w_init_dir.value().c_str(), NULL, IID_PPV_ARGS(&init_directory));
+            HRESULT hr = SHCreateItemFromParsingName(w_init_dir.c_str(), NULL, IID_PPV_ARGS(&init_directory));
             if (FAILED(hr)) return std::unexpected(DialogError::NoSuchDir);
 
             // assign IShellItem*
@@ -378,7 +365,7 @@ namespace yycc::windows::dialog {
         WINCOM::SmartLPWSTR display_name(display_name_ptr);
 
         // convert result and return
-        return ENC::to_utf8(display_name.get()).transform_error([](auto err) { return DialogError::BadEncoding; });
+        return ENC::to_utf8(display_name.get()).value();
     }
 
     /**
diff --git a/src/yycc/windows/dialog.hpp b/src/yycc/windows/dialog.hpp
index e3570a6..0fe3459 100644
--- a/src/yycc/windows/dialog.hpp
+++ b/src/yycc/windows/dialog.hpp
@@ -29,7 +29,6 @@ namespace yycc::windows::dialog {
 
     /// @brief The error occurs in this module.
     enum class DialogError {
-        BadEncoding,     ///< Error occurs when perform encoding convertion.
         TooManyFilters,  ///< The size of file filters list is too large for Windows.
         IndexOverflow,   ///< Default filter index is too large for Windows.
         EmptyFilters,    ///< File filters is empty when picking file.
@@ -310,7 +309,7 @@ namespace yycc::windows::dialog {
     */
     DialogResult<DialogOutcome<std::u8string>> open_folder(const FileDialog& params);
 
-}
+} // namespace yycc::windows::dialog
 
 #undef NS_YYCC_WINDOWS_COM
 
diff --git a/src/yycc/windows/winfct.cpp b/src/yycc/windows/winfct.cpp
index 3235d0e..d16e89d 100644
--- a/src/yycc/windows/winfct.cpp
+++ b/src/yycc/windows/winfct.cpp
@@ -21,7 +21,7 @@ namespace yycc::windows::winfct {
                                        (LPCWSTR) get_current_module,
                                        &hModule);
         if (rv) return hModule;
-        else return std::unexpected(WinFctError::Backend);
+        else return std::unexpected(WinFctError::Win32);
     }
 
     WinFctResult<std::u8string> get_temp_directory() {
@@ -33,7 +33,7 @@ namespace yycc::windows::winfct {
         while (true) {
             if ((expected_size = ::GetTempPathW(static_cast<DWORD>(wpath.size()), wpath.data())) == 0) {
                 // failed, return
-                return std::unexpected(WinFctError::Backend);
+                return std::unexpected(WinFctError::Win32);
             }
 
             if (expected_size > static_cast<DWORD>(wpath.size())) {
@@ -47,7 +47,7 @@ namespace yycc::windows::winfct {
         }
 
         // convert to utf8 and return
-        return ENC::to_utf8(wpath).transform_error([](auto err) { return WinFctError::Encoding; });
+        return ENC::to_utf8(wpath).value();
     }
 
     WinFctResult<std::u8string> get_module_file_name(HINSTANCE hModule) {
@@ -58,7 +58,7 @@ namespace yycc::windows::winfct {
         while (true) {
             if ((copied_size = ::GetModuleFileNameW(hModule, wpath.data(), static_cast<DWORD>(wpath.size()))) == 0) {
                 // failed, return
-                return std::unexpected(WinFctError::Backend);
+                return std::unexpected(WinFctError::Win32);
             }
 
             // check insufficient buffer
@@ -73,7 +73,7 @@ namespace yycc::windows::winfct {
         }
 
         // convert to utf8 and return
-        return ENC::to_utf8(wpath).transform_error([](auto err) { return WinFctError::Encoding; });
+        return ENC::to_utf8(wpath).value();
     }
 
     bool is_valid_code_page(UINT code_page) {
@@ -82,41 +82,32 @@ namespace yycc::windows::winfct {
     }
 
     WinFctResult<void> copy_file(const std::u8string_view& lpExistingFileName, const std::u8string_view& lpNewFileName, BOOL bFailIfExists) {
-        auto wExistingFileName = ENC::to_wchar(lpExistingFileName);
-        auto wNewFileName = ENC::to_wchar(lpNewFileName);
-        if (!(wExistingFileName.has_value() && wNewFileName.has_value())) {
-            return std::unexpected(WinFctError::Encoding);
-        }
+        auto wExistingFileName = ENC::to_wchar(lpExistingFileName).value();
+        auto wNewFileName = ENC::to_wchar(lpNewFileName).value();
 
-        if (!::CopyFileW(wExistingFileName.value().c_str(), wNewFileName.value().c_str(), bFailIfExists)) {
-            return std::unexpected(WinFctError::Backend);
+        if (!::CopyFileW(wExistingFileName.c_str(), wNewFileName.c_str(), bFailIfExists)) {
+            return std::unexpected(WinFctError::Win32);
         }
 
         return {};
     }
 
     WinFctResult<void> move_file(const std::u8string_view& lpExistingFileName, const std::u8string_view& lpNewFileName) {
-        auto wExistingFileName = ENC::to_wchar(lpExistingFileName);
-        auto wNewFileName = ENC::to_wchar(lpNewFileName);
-        if (!(wExistingFileName.has_value() && wNewFileName.has_value())) {
-            return std::unexpected(WinFctError::Encoding);
-        }
+        auto wExistingFileName = ENC::to_wchar(lpExistingFileName).value();
+        auto wNewFileName = ENC::to_wchar(lpNewFileName).value();
 
-        if (!::MoveFileW(wExistingFileName.value().c_str(), wNewFileName.value().c_str())) {
-            return std::unexpected(WinFctError::Backend);
+        if (!::MoveFileW(wExistingFileName.c_str(), wNewFileName.c_str())) {
+            return std::unexpected(WinFctError::Win32);
         }
 
         return {};
     }
 
     WinFctResult<void> delete_file(const std::u8string_view& lpFileName) {
-        auto wFileName = ENC::to_wchar(lpFileName);
-        if (!wFileName.has_value()) {
-            return std::unexpected(WinFctError::Encoding);
-        }
+        auto wFileName = ENC::to_wchar(lpFileName).value();
 
-        if (!::DeleteFileW(wFileName.value().c_str())) {
-            return std::unexpected(WinFctError::Backend);
+        if (!::DeleteFileW(wFileName.c_str())) {
+            return std::unexpected(WinFctError::Win32);
         }
 
         return {};
@@ -144,11 +135,11 @@ namespace yycc::windows::winfct {
         // fetch path
         LPWSTR raw_known_path;
         HRESULT hr = SHGetKnownFolderPath(*pId, KF_FLAG_CREATE, NULL, &raw_known_path);
-        if (FAILED(hr)) return std::unexpected(WinFctError::Backend);
+        if (FAILED(hr)) return std::unexpected(WinFctError::Win32);
         COM::SmartLPWSTR known_path(raw_known_path);
 
         // convert to utf8 and return
-        return ENC::to_utf8(known_path.get()).transform_error([](auto err) { return WinFctError::Encoding; });
+        return ENC::to_utf8(known_path.get()).value();
     }
 
 #endif
diff --git a/src/yycc/windows/winfct.hpp b/src/yycc/windows/winfct.hpp
index 06415da..f0b46f6 100644
--- a/src/yycc/windows/winfct.hpp
+++ b/src/yycc/windows/winfct.hpp
@@ -15,8 +15,7 @@ namespace yycc::windows::winfct {
 
     /// @brief All errors occur in this module.
     enum class WinFctError {
-        Backend,  ///< Error occurs when calling Win32 functions.
-        Encoding, ///< Can not perform encoding convertion.
+        Win32,  ///< Error occurs when calling Win32 functions.
         NoCom,    ///< No COM environment.
     };
 
diff --git a/testbench/CMakeLists.txt b/testbench/CMakeLists.txt
index 731f700..167b75e 100644
--- a/testbench/CMakeLists.txt
+++ b/testbench/CMakeLists.txt
@@ -39,6 +39,7 @@ PRIVATE
     yycc/carton/termcolor.cpp
     yycc/carton/wcwidth.cpp
     yycc/carton/tabulate.cpp
+    yycc/carton/clap.cpp
 )
 target_sources(YYCCTestbench
 PRIVATE
diff --git a/src/yycc/carton/clap/kernel.hpp b/testbench/yycc/carton/clap.cpp
similarity index 100%
rename from src/yycc/carton/clap/kernel.hpp
rename to testbench/yycc/carton/clap.cpp
diff --git a/testbench/yycc/patch/ptr_pad.cpp b/testbench/yycc/patch/ptr_pad.cpp
index 0bc88aa..8d8f420 100644
--- a/testbench/yycc/patch/ptr_pad.cpp
+++ b/testbench/yycc/patch/ptr_pad.cpp
@@ -10,12 +10,11 @@ namespace yycctest::patch::ptr_pad {
 
     TEST(PatchPtrPad, Normal) {
         auto rv = OP::printf(u8"0x%" PRIXPTR_LPAD PRIXPTR, nullptr);
-        EXPECT_TRUE(rv.has_value());
 
 #if defined(YYCC_PTRSIZE_32)
-        EXPECT_EQ(rv.value(), u8"0x00000000");
+        EXPECT_EQ(rv, u8"0x00000000");
 #else
-        EXPECT_EQ(rv.value(), u8"0x0000000000000000");
+        EXPECT_EQ(rv, u8"0x0000000000000000");
 #endif
     }
 
diff --git a/testbench/yycc/string/op.cpp b/testbench/yycc/string/op.cpp
index f7ed3ba..c1102f8 100644
--- a/testbench/yycc/string/op.cpp
+++ b/testbench/yycc/string/op.cpp
@@ -10,8 +10,16 @@ using namespace std::literals::string_view_literals;
 namespace yycctest::string::op {
 
     TEST(StringOp, Printf) {
-        auto rv = OP::printf(u8"%s == %s", u8"Hello World", u8"Hello, world");
-        EXPECT_EQ(rv, u8"Hello World == Hello, world");
+        // UTF8 string
+        {
+            auto rv = OP::printf(u8"%s == %s", u8"Hello World", u8"Hello, world");
+            EXPECT_EQ(rv, u8"Hello World == Hello, world");
+        }
+        // Ordinary string
+        {
+            auto rv = OP::printf("%s == %s", "Hello World", "Hello, world");
+            EXPECT_EQ(rv, "Hello World == Hello, world");
+        }
     }
 
     TEST(StringOp, Replace) {