#include <iostream>
#include <cstring>

int strlen_u8(const char* str)
{
    int I = 0, J = 0;

    while(str[I])
    {
        if ((str[I] & 0xC0) != 0x80)
        {
            ++J;
        }
        ++I;
    }
    return J;
}

int strlen_s_u8(const char* str, unsigned int size)
{
    unsigned int I = 0, J = 0;
    while(I < size)
    {
        if ((str[I] & 0xC0) != 0x80)
        {
            ++J;
        }
        ++I;
    }
    return J;
}

int main()
{
    const char* str = u8"ゴールデンタイムラバー／スキマスイッチ";

    std::setlocale(LC_ALL, "ja_JP.UTF-8");
    std::cout<<strlen_u8(str)<<"\n";
    std::cout<<strlen_s_u8(str, strlen(str))<<"\n";
}