堆栈和二进制表达式树出现双重释放或损坏错误

尝试从堆栈构建二进制表达式树时，出现以下错误。我认为问题在于我正在递归函数中弹出，我认为我正在空栈中弹出但我不知道解决方案。

*检测到glibc ./interp：双重释放或损坏（fasttop）：0x0934d018 * *

这是我的代码：

//This is the main
int main(int argc, char *argv[]){
   TreeNode *node;
   StackNode *stack = NULL;
   push(&stack, "a");
   push(&stack, "b");
   push(&stack, "+");
   //while (emptyStack(stack)!= 1){ //this while loop works correctly, which verifies that my stack implementation is working.
   //  printf("Top is : %s\n", top(stack));
   //  pop(&stack);
   //}
   node = buildTree(stack);


//buildTree function
TreeNode *buildTree(StackNode *stack){
   int integer; //to check for an integer
   char *data = top(stack);
   char *pch = strchr(top(stack), '.'); //to check for a double, looks for the decimal point
   if (emptyStack(stack) != 0){
       //stack is empty
       fprintf(stderr, "Invalid expression, not enough tokens");
       return NULL;
   }
   else if (sscanf(top(stack), "%d", &integer) != 0){
       printf("parser: integer node\n");
       //got an integer
       pop(&stack);
       return makeTreeNode(data, NULL, NULL);
   }
   else if (pch != NULL){
       printf("parser: double node\n");
       //got a double
       pop(&stack);
       return makeTreeNode(data, NULL, NULL);
   }
   else if ( isalpha((int)data[0])){
       //got a variable
       printf("parser: variable node\n");
       pop(&stack);
       return makeTreeNode(data, NULL, NULL);
   }
   else{
       //got an operator, recurse
       printf("parser: operator node\n");
       pop(&stack);
       return makeTreeNode(data,buildTree(stack), buildTree(stack));
   }
}

//makeTreeNode
TreeNode* makeTreeNode(char token[], TreeNode* left, TreeNode* right){
    //this function works correctly

这是我的堆栈函数

StackNode* makeStackNode(char* data, StackNode* next){
   StackNode *node;
   node = malloc(sizeof(StackNode));
   node->data = data;
   node->next = next;
   printf("Making stack node of : %s\n", data);
   return node;
}


char* top(StackNode* stack){
   if (emptyStack(stack)!= 0){
      exit(EXIT_FAILURE);
   }
   else{
      return stack->data;
   }
}

void push(StackNode** stack, char* data){
   StackNode* ptr;
   ptr = makeStackNode(data, *stack);
   *stack = ptr;
   printf("Pushed stack node \n");
}

//pop from stack
void pop (StackNode** stack){
   if (emptyStack(*stack)!=0){
      exit(EXIT_FAILURE);
   }
   else{
      printf("Popping node \n");
      StackNode* ptr = *stack;
      printf("Right before the pop, stack = %s\n", top(*stack));
      *stack = ptr->next;
      printf("Right before the free, stack = %s\n", top(*stack));
      free(ptr);
   } 
}

//returns 1 if stack is empty, 0 if it is not empty
int emptyStack(StackNode* stack){
   if (stack == NULL){
      return 1;
   }
   else{
      return 0;
   }
}

打印输出：

Making stack node of : a
Pushed stack node
Making stack node of : b
Pushed stack node
Making stack node of : +
Pushed stack node
parser: operator node
Popping node
Right before the pop, stack = +
Right before the free, stack = b
parser: variable node
Popping node
Right before the pop, stack = b
Right before the free, stack = a
parser: integer node //this should be a variable node
Popping node
Right before the pop, stack = //this should be stack = a
Right before the free, stack = a  //this should be blank