c++ - How to convert wstring into string?

C++ - How to convert wstring into string?

To convert a std::wstring (wide string) into a std::string (narrow string) in C++, you can use various methods depending on the encoding used and the C++ standard library's capabilities. The common goal is to convert between wide characters (typically UTF-16 or UTF-32) and narrow characters (typically UTF-8).

Here are some methods to perform this conversion:

1. Using std::wstring_convert (C++11 and later)

The std::wstring_convert and std::codecvt facet can be used to convert between wide and narrow strings. However, this is deprecated in C++17 and removed in C++20.

Example (C++11/C++14):

#include <iostream> #include <string> #include <codecvt> // For std::wstring_convert and std::codecvt_utf8 std::string wstring_to_string(const std::wstring& wstr) { std::wstring_convert<std::codecvt_utf8<wchar_t>> conv; return conv.to_bytes(wstr); } int main() { std::wstring wide_str = L"Hello, World!"; std::string narrow_str = wstring_to_string(wide_str); std::cout << "Narrow string: " << narrow_str << std::endl; return 0; }

2. Using std::wstring_convert with UTF-8 Conversion (Modern C++)

Since std::wstring_convert is deprecated, it's recommended to use libraries like iconv, Boost.Locale, or utf8cpp for more reliable and up-to-date conversions.

Using utf8cpp Library:

  1. Include the library: Download and include utf8cpp from its GitHub repository.

  2. Convert using utf8cpp:

#include <iostream> #include <string> #include <utf8cpp/utf8.h> // Include the utf8cpp library std::string wstring_to_string(const std::wstring& wstr) { std::string str; utf8::utf16to8(wstr.begin(), wstr.end(), std::back_inserter(str)); return str; } int main() { std::wstring wide_str = L"Hello, World!"; std::string narrow_str = wstring_to_string(wide_str); std::cout << "Narrow string: " << narrow_str << std::endl; return 0; }

3. Using WideCharToMultiByte (Windows API)

For Windows-specific code, you can use the WideCharToMultiByte function from the Windows API.

Example:

#include <iostream> #include <string> #include <windows.h> std::string wstring_to_string(const std::wstring& wstr) { // Calculate the required buffer size int size_needed = WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), NULL, 0, NULL, NULL); std::string str(size_needed, 0); WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), &str[0], size_needed, NULL, NULL); return str; } int main() { std::wstring wide_str = L"Hello, World!"; std::string narrow_str = wstring_to_string(wide_str); std::cout << "Narrow string: " << narrow_str << std::endl; return 0; }

4. Using C++20 std::u8string

If you are using C++20, you can work with std::u8string for UTF-8 encoded strings.

Example:

#include <iostream> #include <string> std::string wstring_to_string(const std::wstring& wstr) { std::u8string utf8_str = std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>>().to_bytes(wstr); return {utf8_str.begin(), utf8_str.end()}; } int main() { std::wstring wide_str = L"Hello, World!"; std::string narrow_str = wstring_to_string(wide_str); std::cout << "Narrow string: " << narrow_str << std::endl; return 0; }

Summary

  • std::wstring_convert and std::codecvt: Deprecated but still used in older code.
  • utf8cpp library: Modern and reliable for UTF-8 conversion.
  • WideCharToMultiByte: Windows-specific method.
  • C++20 std::u8string: For handling UTF-8 directly.

Choose the method based on your project's requirements and environment.

Examples

  1. "How to convert wstring to string using std::wstring_convert in C++?"

    • Description: Use the std::wstring_convert class from the <locale> header for conversion.
    • Code:
      #include <iostream> #include <string> #include <locale> #include <codecvt> int main() { std::wstring wide_string = L"Hello, World!"; std::wstring_convert<std::codecvt_utf8<wchar_t>> converter; std::string narrow_string = converter.to_bytes(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  2. "How to convert wstring to string using WideCharToMultiByte in Windows API?"

    • Description: Use the WideCharToMultiByte function to perform the conversion on Windows platforms.
    • Code:
      #include <iostream> #include <string> #include <windows.h> int main() { std::wstring wide_string = L"Hello, World!"; int size_needed = WideCharToMultiByte(CP_UTF8, 0, wide_string.c_str(), -1, NULL, 0, NULL, NULL); std::string narrow_string(size_needed, 0); WideCharToMultiByte(CP_UTF8, 0, wide_string.c_str(), -1, &narrow_string[0], size_needed, NULL, NULL); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  3. "How to convert wstring to string using C++11 codecvt facet?"

    • Description: Use std::codecvt_utf8 to perform the conversion in C++11.
    • Code:
      #include <iostream> #include <string> #include <locale> int main() { std::wstring wide_string = L"Hello, World!"; std::wstring_convert<std::codecvt_utf8<wchar_t>> converter; std::string narrow_string = converter.to_bytes(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  4. "How to convert wstring to string using std::string constructor?"

    • Description: Directly construct a std::string from a std::wstring using a suitable constructor.
    • Code:
      #include <iostream> #include <string> int main() { std::wstring wide_string = L"Hello, World!"; std::string narrow_string(wide_string.begin(), wide_string.end()); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  5. "How to handle Unicode characters when converting wstring to string in C++?"

    • Description: Convert std::wstring to std::string while handling Unicode characters.
    • Code:
      #include <iostream> #include <string> #include <locale> #include <codecvt> int main() { std::wstring wide_string = L"Hello, ����!"; std::wstring_convert<std::codecvt_utf8<wchar_t>> converter; std::string narrow_string = converter.to_bytes(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  6. "How to convert wstring to string with UTF-16 encoding in C++?"

    • Description: Handle UTF-16 encoded wide strings and convert them to narrow strings.
    • Code:
      #include <iostream> #include <string> #include <locale> #include <codecvt> int main() { std::wstring wide_string = L"Hello, World!"; std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter; std::string narrow_string = converter.to_bytes(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  7. "How to convert wstring to string using a custom conversion function in C++?"

    • Description: Implement a custom function to convert std::wstring to std::string.
    • Code:
      #include <iostream> #include <string> #include <locale> #include <codecvt> std::string wstring_to_string(const std::wstring& wide_string) { std::wstring_convert<std::codecvt_utf8<wchar_t>> converter; return converter.to_bytes(wide_string); } int main() { std::wstring wide_string = L"Hello, World!"; std::string narrow_string = wstring_to_string(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  8. "How to convert wstring to string without std::codecvt in C++17 and later?"

    • Description: Since std::codecvt is deprecated in C++17, use other methods for conversion.
    • Code:
      #include <iostream> #include <string> #include <locale> #include <stdexcept> std::string wstring_to_string(const std::wstring& wide_string) { std::string narrow_string; std::locale loc(""); std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(loc) .out(std::mbstate_t(), wide_string.data(), wide_string.data() + wide_string.size(), wide_string.data(), std::back_inserter(narrow_string)); return narrow_string; } int main() { std::wstring wide_string = L"Hello, World!"; std::string narrow_string = wstring_to_string(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  9. "How to convert wstring to string using Boost libraries?"

    • Description: Utilize Boost.Locale for conversion between wide and narrow strings.
    • Code:
      #include <iostream> #include <string> #include <boost/locale.hpp> int main() { std::wstring wide_string = L"Hello, World!"; std::string narrow_string = boost::locale::conv::utf_to_utf<char>(wide_string); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

  10. "How to convert wstring to string using std::ostringstream?"

    • Description: Use std::ostringstream to perform the conversion.
    • Code:
      #include <iostream> #include <string> #include <sstream> #include <locale> int main() { std::wstring wide_string = L"Hello, World!"; std::ostringstream converter; converter.imbue(std::locale("")); for (wchar_t wc : wide_string) { converter << static_cast<char>(wc); } std::string narrow_string = converter.str(); std::cout << "Converted string: " << narrow_string << std::endl; return 0; }

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