插入二叉搜索树时出现分段错误

Question

I wrote the following code to insert into binary search tree which can have duplicate entries but i get segmentation fault for larger inputs like greater than 30 ....plz help!! The duplicate entries are stored in the right branch of the node

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

typedef struct vertex{

    int num;
    struct vertex* r;
    struct vertex* l;

} node;


void insert(node* T,int x)
{

    if(x < T->num)
    {
        if(T->l == NULL)
    {
        T->l = (node*)malloc(sizeof(node));
        T->l->num = x;
        printf("%4d ",x);
        return;
    }
        else
    {
        insert(T->l,x);
    }
    }

    else if(x >= T->num)
    {
        if(x == T -> num)

        if(T->r == NULL)
    {
        T->r = (node*)malloc(sizeof(node));
        T->r->num = x;
        printf("%4d ",x);
        return;
    }
        else
        insert(T->r,x);
    }

}



main()
{
    srand((unsigned int)time(NULL));

    int i,n,m,x;
    node* T;

    printf("n = ");
    scanf("%d",&n);
    printf("\nm = ",&m);
    scanf("%d",&m);

    printf("\n\n\n+++ Inserting %d random integers between 1 and %d\n",n,m);

    x = 1 + rand() % m;
    T = (node*)malloc(sizeof(node));
    T->num = x;
    printf("%4d (1)",x);

    for(i=1;i<n;i++)
    {
        x = 1+rand() % m;
        insert(T,x);
        if(i%8 == 7)
    printf("\n");

    }

    printf("\n\n");
}

Answer 1

malloc() does not initialize memory, so set other member to NULL after allocation or use calloc() . Without this you will be accessing random memory when you do T->l or T->r .

T = malloc(sizeof(node));
T->num = x;
T->l = NULL;
T->r = NULL;

or

T = calloc(1, sizeof(node));
T->num = x;

Do this in all places where you use malloc()

Answer 2

malloc(noofbytes) function only allocate noofbytes space only does not initialize with NULL .

This is the problem with your code.

When you allocate memory

T->l = (node*)malloc(sizeof(node));
T->l->num = x;

you allocated memory of size of structure node but it is not initialized . Means

T->l->l and T->l->r is not NULL and have some garbage value.

when you traverse it T->l== NULL or T->r==NULL condition not get satisfied and so it gives segmentation fault.