C allocating array of pointers

[camel-man]

I need some help with this piece of code I wrote earlier, it is compiling correctly but when I try to use my tester program it crashes.


I am trying to create an array of pointers to struct Nodes

typedef struct Node *NodeP;

struct Node
{
	NodeP next;
	EmployeeP info;	
};


struct EmployeeList
{
	NodeP* root;
	int size;
};


EmployeeListP newEmployeeList(int size)
{
	//Creating employeelist and allocating memory for the array or pointers to nodes
	EmployeeListP e=malloc(sizeof(struct EmployeeList));
	e->root=malloc(sizeof(NodeP)* (size*2));
	int i;
	if(e==NULL || e->root==NULL)
	{
		fprintf(stderr,"Failed to allocate memory!\n");
		exit(1);
	}
	//Initializing list size and all pointers to NULL
	e->size=size;
	for(i=0;i<size*2;i++)
	{
		e->root[i]->info=NULL;
		e->root[i]->next=NULL;
	}

	return e;

}

test program where it crashes

#include <stdio.h>
#include <stdlib.h>
#include"Employee.h"
#include"EmployeeList.h"

int main(void)
{
	EmployeeListP e= newEmployeeList(10);

	return 0;
}

 

[Mark44]

This line in your newEmployeeList function looks suspect to me.

e->root=malloc(sizeof(NodeP)* (size*2));

What's the purpose of 2 in the line above?
Also, I think you should cast the value returned by malloc as NodeP.

 

[camel-man]

I have to make the array twice the size of the parameter passed in by the user. I am creating a hash table program and that is one of the specifications.

 

[rcgldr]

During initialization, you haven't allocated any nodes for e->root to use, only the pointers, so all you can do at this point is:

    for(i=0;i<size*2;i++)
    {
        e->root[i] = NULL;
    }

or you could allocate nodes:

    for(i = 0; i < size*2; i++)
    {
        e->root[i] = (NodeP) malloc(sizeof(Node));
        e->root[i]->info = NULL;
        e->root[i]->next = NULL;
    }

 

[LudusRex]

Hello,

Thank you for reaching out for help with your code. From what I can see, the code you have provided looks correct and should be working. However, without the full code and error message, it is difficult to determine what is causing the crash in your tester program.

Here are a few suggestions that may help you troubleshoot and fix the issue:

1. Make sure you are passing the correct size when calling the newEmployeeList function. If the size is too large, it could cause a crash due to memory allocation issues.

2. Check that you are properly accessing the elements of the array in your for loop. It is possible that you are accessing an element out of bounds, which could cause a crash.

3. Ensure that the EmployeeList and NodeP structures are defined correctly in your header files. If there are any discrepancies in the definitions, it could cause issues when accessing the structures in your code.

4. Consider using a debugger to step through your code and see where the crash is occurring. This can help you pinpoint the exact location of the issue.

I hope these suggestions help you resolve the issue with your code. If you continue to experience problems, please provide more information and the full code so I can better assist you. Good luck!