// 按字节截取字符串 utf-8不乱码 func SubstrByByte(str string, length int) string {     bs := []byte(str)[:length]     bl := 0     for i:=len(bs)-1; i>=0; i-- {         switch {         case bs[i] >= 0 && bs[i] <= 127:             return string(bs[:i+1])         case bs[i] >= 128 && bs[i] <= 191:             bl++;         case bs[i] >= 192 && bs[i] <= 253:             cl := 0             switch {             case bs[i] & 252 == 252:                 cl = 6             case bs[i] & 248 == 248:                 cl = 5             case bs[i] & 240 == 240:                 cl = 4             case bs[i] & 224 == 224:                 cl = 3             default:                 cl = 2             }             if bl+1 == cl {                 return string(bs[:i+cl])             }             return string(bs[:i])         }     }     return "" }