segFault in linked-list

[philuu12]

Hi,

Could anyone please show me why the following segfault occurs
at line 54 in the following code?

     1  #include <stdio.h>
     2  #include <stdlib.h>
     3
     4  void printHello()
     5  {   printf("Hello ");  }
     6
     7  void printThere()
     8  {   printf("There\n");  }
     9
    10  void (*FuncPtrArry[2])() = {&printThere,  &printHello};  // Init function pointer array
    11
    12  typedef struct mystruct
    13  {
    14     struct mystruct *next;
    15     void (* funcPtr)();
    16  } NodeStruct;
    17
    18  NodeStruct *topNode = NULL;
    19  NodeStruct *lastNode = NULL;
    20  int count = 2;
    21
    22  void buildlist(void)
    23  {
    24     for (/* count already init to 2 */ ;count > 0; count--)
    25     {
    26          if (topNode == (NodeStruct *)NULL)
    27          {
    28             topNode = (NodeStruct *)malloc(sizeof(NodeStruct));
    29             lastNode = topNode;
    30
    31             if (lastNode == (NodeStruct *)NULL)
    32                  return; /*ERROR */
    33          }
    34          else
    35          {
    36             lastNode -> next = (NodeStruct *)malloc(sizeof(NodeStruct));
    37             if (lastNode -> next == NULL)
    38                  return; /*ERROR */
    39          }
    40
    41          lastNode = lastNode -> next;
    42          lastNode -> funcPtr = FuncPtrArry[count - 1];
    43          lastNode -> next = (NodeStruct *)NULL;
    44     }  // end of for loop
    45  }
    46
    47  int main()
    48  {
    49     buildlist();
    50
    51     while(topNode)
    52     {
    53          (*(topNode->funcPtr)) ();
    54          topNode = topNode->next;
    55     }
    56  }
 

Thanks in advance

Phil

[philuu12]

Output of debugging session:
------------------------------------------
Breakpoint 1, main () at linked_list_net.cc:51
51 while(topNode)
(gdb) n
53 (*(topNode->funcPtr)) ();
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0x00000000 in ?? ()
(gdb)

[Banfa]

Line 42 you set lastNode = lastNode -> next; but lastNode -> next is only set in the else clause of the the if statement so on the first iteration when topNode is created this line causes an error.

Move line 42 into the else clause of the if statement.

[philuu12]

@Banfa
Thank you, Banfa

P.