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POpointer of a pointer in linked list append
 

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    <p>I normally program in python. To increase performance of my simulations, I am learning C. I have a problem to understand the use of a pointer of a pointer when implementing the append function to a linked list. This is an excerpt of the code from my book (Understanding Pointers in C by Kanetkar).</p> <pre><code>#include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; struct node{ int data; struct node *link; }; int main(){ struct node *p; //pointer to node structure p = NULL; //linked list is empty append( &amp;p,1); return 0; } append( struct node **q, int num){ struct node *temp, *r; //two pointers to struct node temp = *q; if(*q == NULL){ temp = malloc(sizeof(struct node)); temp -&gt; data = num; temp -&gt; link = NULL; *q = temp; } else{ temp = *q; while( temp -&gt; link != NULL) temp = temp -&gt; link; r = malloc(sizeof(struct node)); r -&gt; data = num; r -&gt; link = NULL; temp -&gt; link = r; } } </code></pre> <p>In this code, I pass the double pointer **q to the append function. I get that this is the adress of the address, i.e. the adress of NULL in this case. </p> <p>I just don't get <strong><em>why</em></strong> one does it like this. Would it not be valid to remove one * operator from everything in the append() function and simply pass the adress of NULL (i.e. p instead of &amp;p) to the append() function?</p> <p>I have googled this question. The answers are either too hard to understand (since I'm just a C beginner) or too plain. I'm thankful for any hints, comments or links where I can read up about this.</p>
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