C++宽字符与多字节转换技巧

#include <windows.h>
#include <string>
std::string wstr_to_mb(const std::wstring& wstr) {
if (wstr.empty()) return {};
int size_needed = WideCharToMultiByte(CP_UTF8, 0, 
wstr.c_str(), -1, nullptr, 0, nullptr, nullptr);
std::string str(size_needed - 1, 0);
WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), -1, 
&str[0], size_needed, nullptr, nullptr);
return str;
}

std::wstring mb_to_wstr(const std::string& str) {
    if (str.empty()) return {};
    int size_needed = MultiByteToWideChar(CP_UTF8, 0, 
        str.c_str(), -1, nullptr, 0);
    std::wstring wstr(size_needed - 1, 0);
    MultiByteToWideChar(CP_UTF8, 0, str.c_str(), -1, 
        &wstr[0], size_needed);
    return wstr;
}

#include <cstdlib>
#include <locale>
#include <string>
std::wstring mb_to_wstr_c(const std::string& str) {
std::setlocale(LC_ALL, ""); // 使用系统默认locale
size_t len = mbstowcs(nullptr, str.c_str(), 0) + 1;
std::vector<wchar_t> buf(len);
mbstowcs(&buf[0], str.c_str(), len);
return std::wstring(&buf[0]);
}

#include <locale>
#include <codecvt>
#include <string>
std::string wstr_to_utf8(const std::wstring& wstr) {
std::wstring_convert<std::codecvt_utf8<wchar_t>> conv;
return conv.to_bytes(wstr);
}
std::wstring utf8_to_wstr(const std::string& str) {
std::wstring_convert<std::codecvt_utf8<wchar_t>> conv;
return conv.from_bytes(str);
}