QtTest and asserts

[lyuts]

How is it better than:

static float myFunction(float value)
{
    if (value <= 0.0)  // check precondition
    {
        return eNAN;
    }
    return 2 / value;
}

static float myFunction(float value)
{
    if (value <= 0.0)  // check precondition
    {
        return eNAN;
    }
    return 2 / value;
}

To copy to clipboard, switch view to plain text mode 

?

I realize that after your function is completely polished you can remove your assert and doing "if" will not take time. But, I think that your function should be error-resistable, since it gets value inputted by someone. Your function should take care of exceptional/errorneous situation (in your case, it is division by zero).
Lets pretend that your app reads numbers from some file and does divisions for them. This file is created by somebody who put 0 in that file.
Way 1: Your application is crashed by your assert only because someone was not careful enough and put 0 in that file.
Way 2: On processing that division by 0, your application returns NAN value and reports that wrong arguments have been specified.

What would you choose? I think that the 2nd way is more correct.

[doberkofler]

We seem to be moving a little away from my actual question but I'm very interested in this more generic topic as well. My answer to your question would (as always) be: IT DEPENDS!
It depends on what the contract between invoking function and the invoked one specifies and this can be to either not to care at all (most common), return a status and leave it to the caller to decide (your suggestion) or impose a strict rule of parameter passing using a precondition (this is what I wanted to do).

A more realistic (longer) version of myClass::myFunction would typically look like this:

float myClass::myFunction(float value)
{
   /* test consistency of class */
   my_class_invariant(...);
 
   /*test consistency of parameter */
   my_precondition(value > 0, "you are using an invalid value=("+toString(value)+")");
 
   /* usually the algorithms are "little" more complex */
   float temp = 10.0 / value;
 
   /* test consistency of intermediate result */
   my_assert(temp > 0.0 && ...);
 
   /* test consistency of result */
   my_postcondition(fuzzy_compare(temp * value, 10.0);
 
   return temp;
}

float myClass::myFunction(float value)
{
   /* test consistency of class */
   my_class_invariant(...);

   /*test consistency of parameter */
   my_precondition(value > 0, "you are using an invalid value=("+toString(value)+")");

   /* usually the algorithms are "little" more complex */
   float temp = 10.0 / value;

   /* test consistency of intermediate result */
   my_assert(temp > 0.0 && ...);

   /* test consistency of result */
   my_postcondition(fuzzy_compare(temp * value, 10.0);

   return temp;
}

To copy to clipboard, switch view to plain text mode