Question

I have a function that needs to return NULL in some cases and there is another function that needs to test for the return value of this function. I am aware of boost::optional but am not sure how to use the syntax.

Below would be a simple example of said usage:

int funct1(const string& key) {
  // use iterator to look for key in a map
  if(iterator == map.end()) {
    return NULL // need help here!
  else
    return it->second;
}

void funct2(string key) {
  if(funct1(key) == NULL) { // <-- need help here!
    // do something
  } else {
    // do something else
  }

Can someone please help with the syntax?

Thanks.

Answer 1

It stays in the “NULL” state until you set it. You can use this idiom:

optional<int> funct1(const string& key) {
  // use iterator to look for key in a map
  optional<int> ret; 
  if (iterator != map.end()) 
  {
    ret =  it->second;
  }

  return ret;
}

Then:

if (!funct1(key)) { /* no value */ }