判断是不是UTF8字符串，理念是查找所有字符，只要有一个UTF8的就是UTF8文本

bool IsUTF8Text(const void* pBuffer, long size)
{
    bool IsUTF8 = true;
    unsigned char* start = (unsigned char*)pBuffer;
    unsigned char* end = (unsigned char*)pBuffer + size;
    while (start < end)
    {
        if (*start < 0x80) // (10000000): 值小于0x80的为ASCII字符
        {
            start++;
        }
        else if (*start < (0xC0)) // (11000000): 值介于0x80与0xC0之间的为无效UTF-8字符
        {
            IsUTF8 = false;
            break;
        }
        else if (*start < (0xE0)) // (11100000): 此范围内为2字节UTF-8字符
        {
            if (start >= end - 1)
            {
                break;
            }

            if ((start[1] & (0xC0)) != 0x80)
            {
                IsUTF8 = false;
                break;
            }
            start += 2;
        }
        else if (*start < (0xF0)) // (11110000): 此范围内为3字节UTF-8字符
        {
            if (start >= end - 2)
            {
                break;
            }

            if ((start[1] & (0xC0)) != 0x80 || (start[2] & (0xC0)) != 0x80)
            {
                IsUTF8 = false;
                break;
            }
            start += 3;
        }
        else
        {
            IsUTF8 = false;
            break;
        }
    }

    return IsUTF8;
}