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    <p>You need to do it that way for the function to be able to allocate the memory. Simplifying the code:</p> <pre><code>main() { void *p; p = NULL; funcA(&amp;p); int i; i = 0; funcB(&amp;i); } funcA(void **q) { *q = malloc(sizeof(void*)*10); } funcB(int *j) { *j = 1; } </code></pre> <p>This code is done that way so the subfunction <code>funcA</code> can allocate the <code>p</code> pointer. First of all, consider <code>void* p</code> as if it where <code>int i</code>. What you do by doing <code>p = NULL</code> is similar in a way as <code>int i = 0</code>. Now if you pass <code>&amp;i</code> you do not pass the address of <code>0</code>, you pass the address of <code>i</code>. Same thing happens with <code>&amp;p</code> you pass the address of the pointer.</p> <p>Now in funcA, you want to make the allocation, so you use <code>malloc</code> but if you would do <code>q = malloc(...</code> and q would have been <code>void* q</code> in the main function p would not have been allocated. Why? Think of <code>funcB</code>, j holds the address of i, if you want to modify i you would then do <code>*j = 1</code>, because if you would do <code>j = 1</code> then you would have made j point to another memory region instead of i. It is the same with q for funcA. think of it as <code>&lt;type of p&gt;* q</code> it is a pointer to the type of p which is void*, but in case of funcB it is a int. Now you want to modify the address p is pointing at, it means that you do not want to modify the address q is pointing at, you want to modify the pointing address at what q is pointing at, aka <code>*q</code> or <code>p</code>.</p> <p>If it isn't yet clear. Try to think of boxes. I have drawn a quick example with funcA of the boxes involved. Each box has a name (within the box), this box is in the virtual memory of the process at an arbitrary address, and each box contain a value. In this view we are in the state where the <code>funcA(&amp;p)</code> has been called and the malloc will be done.</p> <p><img src="https://i.stack.imgur.com/ek6Tl.png" alt="enter image description here"></p>
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    1. COreally helpful! thank you!
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    2. COBTW: `sizeof(void)` is either zero or an error. Most probably you meant `sizeof (void*)` ?
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    3. COToo long since I have coded in C ;-) thanks, I will update the answer.
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