use an array of node pointers to point to a child of a node

Question

I need a node to point to multiple children (I don't know how many of which I have at compile time).
for the time being I only need the father node to point to at least one child.
but it's pointing to '0', what have I missed?
here is my code

#include <bits/stdc++.h>
using namespace std;

string tokens[10];

typedef struct node
{
    char* value;
    node* children[10]={NULL};
}node;

void connect(node* father,node* child)
{
   // child = (node*) malloc(sizeof(node*));
    if(father->children[0]!=NULL)
        father->children[0]=child;
        cout<<father->children[0]<<endl;
}

int main()
{

node* father_ = (node*) malloc(sizeof(node*));
node* child_ = (node*) malloc(sizeof(node*));
cout<<"before\n";
connect(father_,child_);
cout<<"after\n";

father_->children[0]->value="a";
cout<<child_->value;

}

http://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h — πάντα ῥεῖ, Apr 17 '16 at 11:28
I wanted to write an answer to your question but it would be only quoting chapters from any C++ book. Try searching for dynamic memory allocation in C++; constructors, destructors and RAII; linked list and data structures. — Teivaz, Apr 17 '16 at 11:38
@underscore_d go to the link provided by πάντα ῥεῖ to check out what that header does, however I only used it because this is a quick prototype. — Aly Shmahell, Apr 17 '16 at 18:58

Thomas · Answer 1 · 2016-04-17T11:45:07.480

2

What's the obsession with pointers? Here a more c++ version.

#include <string>
#include <vector>
#include <iostream>
#include <memory>

struct node
{
    std::string value;
    std::vector<node*> children;
};

void connect(node* father,node* child)
{
    father->children.push_back(child);
}

int main()
{
    auto father = std::make_unique<node>();
    auto child = std::make_unique<node>();

    connect( father.get(), child.get());

    father->children[0]->value="a";

    std::cout << child->value;
}

Live on Coliru

Note:

avoid using naespace std
don't use malloc and free
you don't need to typedef struct in c++
use containers such as string and vector
avoid c style arrays
don't use raw pointers for ownership

edited Apr 17 '16 at 11:45

answered Apr 17 '16 at 11:39

Thomas

4,980
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your code simply works, and I like the pure C++ approach you provided, pretty neat. – Aly Shmahell Apr 17 '16 at 19:37
While I could have fixed your issue, I though it better to provide a solution that avoids the problem. – Thomas Apr 17 '16 at 20:25
I appreciate your help, truly. while I couldn't completely steer away from pointers in this particular project, I found it useful to use vectors to avoid pointing to pointers. however using c++14 methods and variables is not applicable in my situation. – Aly Shmahell Apr 18 '16 at 01:34

bipll · Accepted Answer · 2016-04-18T06:43:59.530

1

if(father->children[0]!=NULL)
    father->children[0]=child;

You only instantiate a father-child relation if the father already has a non-null first child. Change != into == (or even drop that !=NULL part, but then negate the condition).

edited Apr 18 '16 at 06:43

answered Apr 17 '16 at 11:42

bipll

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use an array of node pointers to point to a child of a node

2 Answers2