智能合约如何实现字符串连接

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pragma solidity >=0.4.23;
cotract JoinString{
    function connectAtring(string a,string b) returns(string){
        bytes _a=bytes(a)
        bytes _b=bytes(b)
        
        string connect=string(_a.length+_b.length)
        bytes _c=bytes(connect)
        for(uint i=0;i<=_a.length;i++){
            _c[i]=_a[i]
        }
        for(uint i=0;i<=_b.length;i++){
            _c[_b.length+i]=_b[i]
        }
        return string(_c)
    }
}