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I am try to compare a string variable in solidity code, mainly i have to check if the string is empty or not. How can it be achieved and also how much long/large of a string i can save in a string variable.

contract BOLData{
struct Data {
    string sData;
    string ssCompanyData;
    string ConsigneeData;
    string BOL_ID;
}

mapping(string => Data) private BOL_Data;
//Add the initial value 
function BOLData (string s_Data, string  bolid)
{
    BOL_Data[bolid] = Data(s_Data,'', '', bolid);
}
//Add data, hash to Block Chain
function addData(string ssCompany_Data, string Consignee_Data, string bolid) public {
    string s_DataO = BOL_Data[bolid].sData;
    string ssCompany_DataO = BOL_Data[bolid].ssCompanyData;
    string Consignee_DataO = BOL_Data[bolid].ConsigneeData;
    if(ssCompany_DataO == '')
    {}
    BOL_Data[bolid] = Data(s_DataO,ssCompany_Data, Consignee_Data, bolid);
}

//Fetch data, hash values from block chain
function getData(string DataID) returns (string, string, string){
    string s_Data = BOL_Data[DataID].sData;
    string ssCompany_Data = BOL_Data[DataID].ssCompanyData;
    string Consignee_Data = BOL_Data[DataID].ConsigneeData;
    return(s_Data, ssCompany_Data, Consignee_Data);
}

}

1

A string can be of any size, there is no limit.

You can check if a string memory str is empty like this:

if (bytes(str).length == 0)
{
    // String is empty...
}

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