Question

I want to write a cpp function something similar to this, where outVal should accept data of the corresponding type returned from the respective functions in each case.

void ReadFieldByType(char fieldType, string content, string& outStr, **unknown**& outVal){
unsigned int ifield;
char cField;
string sField;
double dField;
switch (fieldType)
                {
                case 'c':
                ReadChar(content, content, cField);
                outVal = cField;
                break;
                case 'd':
                ReadInteger(content, content, ifield);
                outVal = ifield;
                break;
                case 'f':
                ReadDouble(content, content, dField);
                outVal = dField;
                break;
                case 's':
                ReadString(content, content, sField);
                outVal = sField;
                break;
                default:
                break;
                }
                outStr = content;}

I don’t know how to set datatype for outVal. Can this be improved or is there any other choice to accomplish this task?

Answer 1

You could probably do it with templates and the typeid operator:

template<class T>
void ReadField(string content, string& outStr, T& outVal)
{
    if (typeid(T) == typeid(int))
        ReadInteger(content, content, outVal);
    else if (typeid(T) == typeid(char))
        ReadChar(content, content, outVal);
    else if (typeid(T) == typeid(double))
        ReadDouble(content, content, outVal);
    else if (typeid(T) == typeid(std::string))
        ReadString(content, content, outVal);

    outStr = content;
}

Although I have to admit that I don’t like the solution.