What is the best way to return an error from a function when I'm already returning a value?

Question

I wrote a function in C that converts a string to an integer and returns the integer. When I call the function I also want it to let me know if the string is not a valid num

Answer 1

You can either return an instance of a class where a property would be the value interested in, another property would be a status flag of some sort. Or, pass in an instance of the result class..

Pseudo code
  MyErrStatEnum = (myUndefined, myOK, myNegativeVal, myWhatever)

ResultClass
  Value:Integer;
  ErrorStatus:MyErrStatEnum

Example 1:

result := yourMethod(inputString)

if Result.ErrorStatus = myOK then 
   use Result.Value
else
  do something with Result.ErrorStatus

free result

Example 2

create result
yourMethod(inputString, result)

if Result.ErrorStatus = myOK then 
   use Result.Value
else
  do something with Result.ErrorStatus

free result

The benefit of this approach is you can expand the info coming back at any time by adding additional properties to the Result class.

To expand this concept further, it also applies to method calls with multiple input parameters. For example, instead of CallYourMethod(val1, val2, val3, bool1, bool2, string1) instead, have a class with properties matching val1,val2,val3,bool1,bool2,string1 and use that as a single input parameter. It cleans up the method calls and makes the code more easily modified in the future. I'm sure you've seen that method calls with more than a few parameters is much more difficult to use/debug. (7 is the absolute most I would say.)