What would be a proper invalid value for a pointer?

Question

Suppose I have this code. Your basic \"if the caller doesn\'t provide a value, calculate value\" scenario.

void fun(const char* ptr = NULL)
{
   if (ptr==NULL) {         


        

Answer 1

Using overloaded versions of the same function for different input is best, but if you want to use a single function, you could make the parameter be a pointer-to-pointer instead:

void fun(const char** ptr = NULL) 
{ 
   if (ptr==NULL) { 
      // calculate what ptr value should be 
   } 
   // now handle ptr normally 
} 

Then you can call it like this:

fun();

.

char *ptr = ...; // can be NULL
fun(&ptr);