Reading an optional argument

The source code has now been modified. The argument type DaysPerYear has been changed:

extern "C" __declspec( dllexport )
LPXLOPER HISTVOL(const COper* Prices, const COper* DaysPerYear)
{
    ...
}

In addition, a new local variable valDaysPerYear, has been declared, and some lines have been generated to populate it.

extern "C" __declspec( dllexport )
LPXLOPER HISTVOL(const COper* Prices, const COper* DaysPerYear)
{
    CXlOper xloResult;
    BOOL bOk = TRUE;
    std::vector<double> vecPrices;
    bOk = bOk && Prices->ReadVector(vecPrices, "Prices", xloResult);
    double valDaysPerYear = 250.0;                                                     
    bOk = bOk && DaysPerYear->ReadOptional(valDaysPerYear, "DaysPerYear", xloResult);  
    if (!bOk)
        return xloResult.Ret();
//}}XLP_SRC

Notice that the local variable is first initialised to the value (250.0) that we specified in the Function Wizard. Then the ReadOptional() method is called, which will do one of the following:

• If the input DaysPerYear contains a numeric value, then it will be converted to a double and put into the local variable. The method will return TRUE to indicate success.
• If the input is empty or missing, then the local variable will be left unchanged. The method will return TRUE to indicate success.
• If the input is not empty or missing, and the value cannot be converted to a double then the local variable will be left unchanged, and an error string will be put into xloResult. The method will return FALSE to indicate failure.

Change your code to use the new local variable, so that it reads as shown below:

extern "C" __declspec( dllexport )
LPXLOPER HISTVOL(const COper* Prices, const COper* DaysPerYear)
{
    CXlOper xloResult;
    BOOL bOk = TRUE;
    std::vector<double> vecPrices;
    bOk = bOk && Prices->ReadVector(vecPrices, "Prices", xloResult);
    double valDaysPerYear = 250.0;                                                     
    bOk = bOk && DaysPerYear->ReadOptional(valDaysPerYear, "DaysPerYear", xloResult);  
    if (!bOk)
        return xloResult.Ret();
//}}XLP_SRC

    double dHistVol;
    if (CalcHistVol(vecPrices.begin(), vecPrices.size(), valDaysPerYear, &dHistVol))
        xloResult = dHistVol;
    else
        xloResult = xlerrNum;
    return xloResult.Ret();
}

This technique can also be used to read in optional boolean, integer and string values. For more details see COper::ReadOptional() in the class reference.

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