Overwriting function parameter in a recursive function?

Question

So I have a class that has a protected pointer member of the following type

int *assigntoThis; // In the constructor I have initialized this to NULL.

I also have a public recursive member function of the same class with the following declaration

bool find(int* parent, std::string nameofnode, int* storeParentinThis);

The recursive function checks through child nodes and if the name of the child Node matches the string passed in as a parameter it will assign the address of parent to storeParentinThis.

This is how I call the function from another function of the same class.

bool find(root, "Thread", assigntoThis);

However, during runtime when I output the value stored in assigntoThis I get 00000000 = NULL. How do I change the value of assigntoThis inside my recursive function?

For future reference here is the thread for the reasoning behind this question stackoverflow.com/questions/1898524/… — user1084113
– user1084113, Commented Jul 11, 2012 at 19:01

marcinj · Accepted Answer · 2012-07-11 20:44:41Z

change to :

bool find(int* parent, std::string nameofnode, int*& storeParentinThis);

explanation:

here is a simplified version of your original code:

foo (int* p) { /// p bahaves as a local variable inside foo
  p = 1;  
}    
int* p = 0;
foo(p);
// here p is still equal 0

this is actually similar to following code:

foo (int i) {
  i = 1;  
}    
int i = 0;
foo(i);
// here i is still equal 0

which I think is easier to understand.

So if we want to return something from a function we must make a pointer to it or a reference to it, going backwards with examples:

foo (int* i) { // pointer example
  *i = 1;  
}    
int i = 0;
foo(&i);
// here i is equal to 1

foo (int& i) { // using reference example
  i = 1;  
}    
int i = 0;
foo(i);
// here i is equal to 1

Now it is easy to apply it to your case:

// pointer example
bool find(int* parent, std::string nameofnode, int** storeParentinThis) {
    *storeParentinThis = parent;
}

// reference example
bool find(int* parent, std::string nameofnode, int*& storeParentinThis) {
     storeParentinThis = parent;
}

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