判断char*是否为utf8编码

int utf8_check(const char* str,size_t length){    size_t i = 0;    int nBytes = 0;////UTF8可用1-6个字节编码,ASCII用一个字节    unsigned char ch = 0;    bool bAllAscii = true;//如果全部都是ASCII,说明不是UTF-8    while(i < length)    {        ch = *(str + i);         if ((ch & 0x80) != 0)            bAllAscii = false;        if(nBytes == 0)        {            if((ch & 0x80) != 0)            {                while((ch & 0x80) != 0)                {                    ch <<= 1;                    nBytes ++;                }                if((nBytes < 2) || (nBytes > 6))                {                    return 0;                }                nBytes --;            }        }        else        {            if((ch & 0xc0) != 0x80)            {                return 0;            }            nBytes --;        }        i ++;    }    if(bAllAscii)        return false;    return (nBytes == 0);}