Question

I am trying to pass a queue to another function in c in order to make some operations on it, I’ve tried to send it’s reference and put in a pointer in the function arguments but that doesn’t make sense!

here’s what I did:

this is the caller:

G = my_job(&qu, inducing_cell, target_cell, G, vertices_number, cells_number);

this is the function:

graph* my_job(Queue *qu, Position inducing_cell, Position target_cell, graph* G, unsigned long vertices_number, unsigned long cells_number) {}

Answer 1

You need to pass in the address of a variable to a Queue struct.

So as follows:

 Queue q; //create a queue instance
 G =  my_job(&q /*Pass in address to Q*/, inducing_cell, target_cell, G, vertices_number, cells_number);

Or you can create a pointer to a Queue and pass that in:

 Queue* q = malloc(sizeof(Queue)); //Make sure you have allocated the pointer (unless my_job allocates it inside)
 G = my_job(q /*Pass in pointer (pointer is copied)*/, inducing_cell, target_cell, G, vertices_number, cells_number);
 //Do stuff with q
 free(q); // Free the memory. 

If you want to pass in a pointer to alter what it points to and see the changes when the function returns, you’ll need to pass in a Queue** because a pointer is passed by value, ie it’s copied into the function. So if you change what it points to inside, that change is not seen when the function returns.