string str="[sernumber=1dsadasdcn=code22323][sernumber=1dsadasdcn=[code2]22323][sernumber=1dsadasdcn=code22323][sernumber=1dsadasdcn=code22323]"
需要取第外层[]，是最外层还是第n层？这个可以用递归平衡组https://www.xuebuyuan.com/2139326.html