常用字符串编码转换的函数

#include <windows.h>
#include <string>

/// @brief ascii和unicode之间的编码转换 
size_t ascii_to_unicode(const char* src, wchar_t* dest, size_t dest_len, size_t src_len = 0)
{
    if(src_len == 0)
        src_len = strlen(src);
    return MultiByteToWideChar(CP_ACP, 0, src, static_cast<int>(src_len), 
        dest, static_cast<int>(dest_len));
}
size_t unicode_to_ascii(const wchar_t* src, char* dest, size_t dest_len, size_t src_len = 0)
{
    if(src_len == 0)
        src_len = wcslen(src);
    return WideCharToMultiByte(CP_ACP, 0, src, static_cast<int>(src_len), 
        dest, static_cast<int>(dest_len), NULL, NULL);
}
/// @brief utf8和unicode之间的编码转换 
size_t utf8_to_unicode(const unsigned char* src, wchar_t* dest, size_t dest_len, size_t src_len = 0)
{
    if(src_len == 0)
        src_len = strlen((const char*)src);
    return MultiByteToWideChar(CP_UTF8, 0, (const char*)src, static_cast<int>(src_len), 
        dest, static_cast<int>(dest_len));
}

size_t unicode_to_utf8(const wchar_t* src, unsigned char* dest, size_t dest_len, size_t src_len = 0)
{
    if(src_len == 0)
        src_len = wcslen(src);
    return WideCharToMultiByte(CP_UTF8, 0, src, static_cast<int>(src_len), 
        (char*)dest, static_cast<int>(dest_len), NULL, NULL);
}
/// @brief ascii和utf8之间的编码转换 
size_t ascii_to_utf8(const char* src, unsigned char* dest, size_t dest_len, size_t src_len = 0)
{
    if(src_len == 0)
        src_len = strlen(src);
    std::wstring unicode(src_len, 0);
    unicode.resize(
        ascii_to_unicode(src, const_cast<wchar_t*>(unicode.data()), unicode.size(), src_len));
    return unicode_to_utf8(unicode.data(), dest, dest_len, unicode.size());
}
size_t utf8_to_ascii(const unsigned char* src, char* dest, size_t dest_len, size_t src_len = 0)
{
    if(src_len == 0)
        src_len = strlen((const char*)src);
    std::wstring unicode(src_len * 2, 0);
    unicode.resize(
        utf8_to_unicode(src, const_cast<wchar_t*>(unicode.data()), unicode.size(), src_len));
    return unicode_to_ascii(unicode.data(), dest, dest_len, unicode.size());
}

/// @brief 普通字符串转宽字符串 
std::wstring& to_wstring(const char* str, size_t len, std::wstring& ret)
{
    if(len == 0)
        len = strlen(str);
    ret.resize(len);
    ret.resize(ascii_to_unicode(str, const_cast<wchar_t*>(ret.data()), ret.size(), len));
    return ret;
}
std::wstring to_wstring(const char* str, size_t len = 0)
{
    std::wstring ret;
    return to_wstring(str, len, ret);
}
std::wstring to_wstring(const std::string& str)
{
    std::wstring ret;
    return to_wstring(str.data(), str.size(), ret);
}
std::wstring& to_wstring(const std::string& str, std::wstring& ret)
{
    return to_wstring(str.data(), str.size(), ret);
}
/// @brief 宽字符串转普通字符串 
std::string& to_string(const wchar_t* str, size_t len, std::string& ret)
{
    if(len == 0)
        len = wcslen(str);
    ret.resize(len * 2);
    ret.resize(unicode_to_ascii(str, const_cast<char*>(ret.data()), ret.size(), len));
    return ret;
}
std::string to_string(const wchar_t* str, size_t len)
{
    std::string ret;
    return to_string(str, len, ret);
}
std::string to_string(const std::wstring& str)
{
    std::string ret;
    return to_string(str.data(), str.size(), ret);
}
std::string& to_string(const std::wstring& str, std::string& ret)
{
    return to_string(str.data(), str.size(), ret);
}

}