c++ - Passing "constant pointers" to functions -

i've written program performs various operations on binary tree. @ beginning set null root pointer, call couple of insert() functions add new nodes tree.

finally, call search() function finds requested structure node , returns it.

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insert() function takes 2 parameters - reference root pointer, , constant int key, converted node structure , added tree

search() function takes "constant root pointer" - not reference, because want operate on local pointer directly, , don't want changed. other argument takes int key.

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this whole program:

#include <iostream>  struct node {     node *p; // parent     node *left, *right;     int key; };  void insert(node *&root, const int key) {     node newelement = {};     newelement.key = key;      node *y = null;     while(root)     {         if(key == root->key) exit(exit_failure);         y = root;         root = (key < root->key) ? root->left : root->right;     }      newelement.p = y;      if(!y) root = &newelement;     else if(key < y->key) y->left = &newelement;     else y->right = &newelement; }  node* search(const node *root, const int key) {     while( (root) && (root->key != key) )         root = (key < root->key) ? root->left : root->right;      return root; }  int main() {     using namespace std;     node *root = null;     insert(root, 5);     insert(root, 2);      cout << search(root, 5)->key << endl;     return 0; } 

my question - why doesn't search function work? displays error - return value type not match function type. return poiner, says in declaration!

also, "const" keyword here o.k.?

root const node*, , return value node*. should changed const node*.

const node* search(const node *root, const int key); 

if need search function give non-const node, needs take non-const node parameter. can provide overload allow both possibilities

node* search(node *root, const int key);