CODEWITHSUNDEEP
c++pass-by-reference
Mr Jedi
Mr Jedi

Reputation: 34645

How to pass argument to function - dealing with reference

I have some problems with C++. I build application using GAlib library (it's a C++ Library of Genetic Algorithm Components - http://lancet.mit.edu/ga/).

In one of examples (full code of example: http://lancet.mit.edu/galib-2.4/examples/ex6.C) author create function that initializes tree:

void TreeInitializer(GAGenome & c)
{
  GATreeGenome<int> &child=(GATreeGenome<int> &)c;

// destroy any pre-existing tree
  child.root();
  child.destroy();

// Create a new tree with depth of 'depth' and each eldest node containing
// 'n' children (the other siblings have none).
  int depth=2, n=2, count=0;
  child.insert(count++,GATreeBASE::ROOT);

  for(int i=0; i<depth; i++){
    child.eldest();
    child.insert(count++);
    for(int j=0; j<n; j++)
      child.insert(count++,GATreeBASE::AFTER);
  }
}

He invoke function in that way:

genome.initializer(TreeInitializer);

and He don't pass an argument. When I trying pass argument to that function by changing declaration for example:

void TreeInitializer(GAGenome &, int deph);

Compiler shows me errors. I don't know how to invoke this function properly. I know it's related to reference but passing (or not passing) argument in that way is new to me.

How to pass more arguments to that function?

Upvotes: 0

Views: 119

Answers (2)

riv
riv

Reputation: 7324

The line genome.initializer(TreeInitializer); does not call TreeInitializer - instead, it passes the pointer to that function to genome.initializer, so it can call it with whatever arguments it needs/multiple times. If you want TreeInitializer to accept more arguments, you need to modify the initializer to accept a different type of function. It is probably defined as

void initializer(void (*f)(GAGenome&))
{
    // ...
    f(genome);
    // ...
}

You need to change the argument type to void (*f)(GAGenome&, int) and change the lines that call f.

On the other hand, if you can't modify the initializer function but want to be able to specify the depth, then the best you can do is make a global variable that you set to whatever depth you need and have TreeInitializer use that variable. It isn't a clean solution if you think global variables are evil, but it's your only choice if the initializer doesn't let you supply any "context".

Upvotes: 2

peterh
peterh

Reputation: 12575

What you what to do in

GATreeGenome<int> &child=(GATreeGenome<int> &)c;

is a casting from a GAGenome to GATreeGenome . If you haven't a casting operator for this case, it won't work...

Upvotes: -1

Related Questions