segmentation fault - pointer handling

[jcmargentina]

I am new with C, and I am having problems with this simple code.

I get segmentation fault when run.

Can someone please help me understand the problem here?

#include <stdio.h>
#include <stdlib.h>

struct node {
    int value;
    struct node* left;
    struct node* right;
};

struct node* new_node(int);
void insert_value_in_tree(struct node*, int);

struct node* root = NULL;

void main() {
    insert_value_in_tree(root, 1);
    printf("%d", root->value);
}

void insert_value_in_tree(struct node* node, int value)
{
    if (!node) {
        node = new_node(value);
        return;
    }
}

struct node* new_node(int value)
{
    struct node* node = (struct node *) malloc(sizeof(struct node));
    node->value = value;
    node->left = node->right = NULL;
    return node;
}

[Repeater]

In line 17, root is null.

You are passing a COPY of root to the function insert_value_in_tree, so the COPY is being set.

[jcmargentina]

root is a pointer, and I though that doing:

insert_value_in_tree(root, 1);

I would be passing the address of the pointer "root" to the function. Also I declared the first parameter as pointer.

How can I fix this?

[Repeater]

A pointer is treated like any other variable. If you pass it by value, as you are, the receiving function gets a COPY.

If you want the receiving function to be working with the original, not a copy, then pass it by reference:

#include <stdio.h>
#include <stdlib.h>

struct node {
    int value;
    struct node* left;
    struct node* right;
};

struct node* new_node(int);
void insert_value_in_tree(node*&, int);

struct node* root = NULL;

int main() {
    insert_value_in_tree(root, 1);
    printf("%d", root->value);
}

void insert_value_in_tree(node*& node, int value) // Pass by REFERENCE, with '&'
{
    if (!node) {
        node = new_node(value);
        return;
    }
}

struct node* new_node(int value)
{
    struct node* node = (struct node *) malloc(sizeof(struct node));
    node->value = value;
    node->left = node->right = NULL;
    return node;
}