title: Malloc header contents
body: <p>So in most implementations malloc stores an header before the allocated memory to keep track of  the allocated memory size (so that it can do free and recalloc). What are the header contents?</p>
  
  <p>I wrote a naive code to find it but it doesn't make any sense</p>
  
  <pre><code>int * ptr;
  ptr = malloc(12*sizeof(int));
  printf("Header = %d\n",*(ptr-1));
  </code></pre>
  
  <p>It returns</p>
  
  <pre><code>Header = 57
  </code></pre>
  
  <p>What is happening here?</p>