I get the Error CS0177 (The output parameter...must be assigned to before control...).Althoug looked to similar entries couldn't fix it

Question

With the code below I am reading process variables from a PLC controller. The method has outputs like var_result and var_result_float. I get the Error CS0177 in the last line regarding that these output parameters are not assigned.In the second for loop I had assigned them values for all conditions. I cannot find what is wrong.

Error CS0177 The out parameter 'var_result' must be assigned to before control leaves the current method...

Error CS0177 The out parameter 'var_result_float' must be assigned to before control leaves the current method...

public Int32 doReadMixEx2(Int32 connnr, Int32 timeout, string var_type, string var_format, UInt16 var_offset, UInt16 var_bit, UInt16 var_DB_no, out UInt32 var_result, out Single var_result_float)
    {
        Int32 result = AGL4.AGL40_PARAMETER_ERROR;
        AGL4.DATA_RW40[] rwfield = new AGL4.DATA_RW40[1];
        for (int j = 0; j <= 2; j++)
        {                
            rwfield[j] = new AGL4.DATA_RW40();
            rwfield[j].BitNr = var_bit;
            rwfield[j].DBNr = var_DB_no;
            rwfield[j].Offset = var_offset;
            rwfield[j].OpAnz = 1;
            rwfield[j].Result = 0;

            switch (var_type)
            {
                case "M":
                    rwfield[j].OpArea = AGL4.AREA_FLAG;
                    break;

                case "I":
                    rwfield[j].OpArea = AGL4.AREA_IN;
                    break;
                case "O":
                    rwfield[j].OpArea = AGL4.AREA_OUT;
                    break;
            }

            PLC__VAR_vartype = var_type;

            switch (var_format)
            {
                case "X":
                    rwfield[j].OpType = AGL4.TYP_BIT;
                    rwfield[j].B = new Byte[rwfield[0].OpAnz];
                    rwfield[j].B[0] = 0;
                    break;

                case "B":
                    rwfield[j].OpType = AGL4.TYP_BYTE;
                    rwfield[j].B = new Byte[rwfield[0].OpAnz];
                    rwfield[j].B[0] = 0;
                    break;
             }

        }

        result = AGL4.ReadMixEx(connnr, rwfield, rwfield.Length, timeout);
        Return_ReadMixEx = result;

        for (int j = 0; j <= 2; j++)
        {
            if (result != AGL4.AGL40_SUCCESS)
            {
                // Error happened.
                String errormsg = "";
                AGL4.GetErrorMsg(result, out Error_Message_ACCON);
                var_result = 0;
                var_result_float = 0;
            }
            else
            {
                switch (var_format)
                {
                    case "X":
                        var_result = rwfield[j].B[0];
                        var_result_float = 0;
                        break;
                    case "B":
                        var_result = rwfield[j].B[0];
                        var_result_float = 0;
                        break;                      
                }
            }
        }

        return result;  // Here I get the Error        


    }

Answer 1

You are right in saying you are assigning a value to the variable, the problem however is that there is a case/branch where you wont be assigning a value to the variable.

For example: If result == AGL4.AGL40_SUCCESS you will go to the else. If your var_format variable is not X or B you wont match any of the switch conditions and the var_result will never be assigned.

Looking at the code you provide. var_result and var_result_float will always be 0. I would therefore suggest you assign them at the start of the method.

public Int32 doReadMixEx2(Int32 connnr, Int32 timeout, string var_type, string var_format, UInt16 var_offset, UInt16 var_bit, UInt16 var_DB_no, out UInt32 var_result, out Single var_result_float)
{
    var_result = 0;
    var_result_float = 0;
    Int32 result = AGL4.AGL40_PARAMETER_ERROR;
    AGL4.DATA_RW40[] rwfield = new AGL4.DATA_RW40[1];
        
    //Rest of your code

    return result; 
}