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POTwo Digit Pointer? How did this happen?
 

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  1. POTwo Digit Pointer? How did this happen?
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    <p>So on a project I'm working on I'm getting the following error:</p> <pre><code>*** glibc detected *** ./social_network: munmap_chunk(): invalid pointer: 0x09a913b0 *** </code></pre> <p>A few printf statements revealed the the struct I'm freeing that causes this error has a memory address of....17. So how is this possible? What could have happened to make this appear...?</p> <p>Here's some output right before the crash:</p> <pre><code>temp is: 162075592 temp user is 162075408 After free of temp inside while loop, first line before free of temp temp is: 162075760 temp user is 162075480 After free of temp inside while loop, first line before free of temp temp is: 162075568 temp user is 17 </code></pre> <p>And here's the code that outputs the output</p> <pre><code> 21 void destroy() { 22 23 struct user_node *node; 24 25 struct friend_node *temp; 26 struct friend_node *next_temp; 27 28 //iterate over the list of users 29 while (*head != NULL) { 30 printf("before a_friend\n"); 31 temp = (*head)-&gt;a_friend; 32 33 //Iterate over friends of users, free friend nodes 34 while (temp != NULL) { 35 printf("inside while loop, first line\n"); 36 next_temp = temp-&gt;next_friend; 37 printf("before free of temp\n"); 38 printf("temp is: %d\n", (int) temp); 39 printf("temp user is %d\n", (int)temp-&gt;user); 40 free(temp); &lt;==================================SEGFAULT IS HERE!!!!!!!!!!!!! 41 printf("After free of temp\n"); 42 temp = next_temp; 43 next_temp = NULL; 44 } 45 46 node = (*head)-&gt;next_user; 47 printf("before free of: %s\n", (*head)-&gt;name); 48 free(*head); 49 printf("after free of that person...\n"); 50 *head = node; 51 printf("*head = node afterwards\n"); 52 node = NULL; 53 } 54 printf("before final free...\n"); 55 free(head); 56 } </code></pre> <p>EDIT:</p> <p>struct friend_node</p> <pre><code> 23 //node used to store a pointer to a user_node and next friend 24 struct friend_node { 25 struct friend_node *next_friend; 26 struct user_node *user; 27 }; </code></pre> <p>struct user_node</p> <pre><code> 12 //Struct definitions 13 //node used to store information about a user 14 struct user_node { 15 char name[21]; 16 int age; 17 int gender; 18 char location[21]; 19 struct friend_node *a_friend; 20 struct user_node *next_user; 21 }; 22 </code></pre>
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    1. COWill you please give the definition of `struct friend_node`?
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    2. COsure thing, added the struct friend_node as well as struct user_node definitions above
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    3. COIf you have user A, B, C - C is a friend of both A & B. When creating lists of friends for User A & User B, do you create separate friend wrappers for C for A & B or do you reuse the same friend wrapper at both places?
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