Changing malloc to new operator

Question

I am changing a path planning code from C to C++. The code dynamically allocates the states in map. I don't clearly understand the difference between new and malloc. I get an error for following snippet of code.

typedef struct cell
{ 
   int x,y;
   struct cell *n[5];
}cell_t;

typedef struct pq
{
   cell_t **heap;
   int len,cap;
}pq_t;

//for C version
func(pq_t *pq,50)
{
   pq->heap = malloc(sizeof(cell)*50);
   pq->len = 0;
   pq->cap = 0;
}
//for C++ version
func(pq_t *pq,50)
{
   pq->heap = (cell_t*)::operator new(sizeof(cell_t)*50);
   pq->len = 0;
   pq->cap = 0;
}

The error I get is :

cannot convert ‘cell_t* {aka cell*}’ to ‘cell_t** {aka cell_s**}’ in assignment

pq->heap =(cell_t*) ::operator new (sizeof(cell_t) * (50));""

What do I need to change?

Answer 1

Instead of this:

pq->heap = (cell_t*)::operator new(sizeof(cell_t)*50);

You want this:

pq->heap = new cell_t[50];

That said, it's clear that the code you've posted is not quite your real code, so there could be some additional mistake in there. Maybe update your question with real code that compiles.