解决 C 警告 - 取消引用 null 指针

Question

This is the bug report from facebook infer.

error: NULL_DEREFERENCE
  pointer `stack` last assigned on line 24 could be null and is dereferenced at line 25, column 5.
  22. struct string_stack* create_String_Stack(unsigned capacity)
  23.   {
  24.       struct char_stack* stack = calloc(1,sizeof(struct char_stack));
  25. >     stack-> capacity = capacity;
  26.       stack->top = -1;
  27.       stack->array = (char*)malloc(stack->capacity * sizeof(char));

struct char_stack
{
    int top;
    unsigned capacity;
    char* array;
};

How can get rid of this warning?

Answer 1

I believe the problem is at struct char_stack* stack = calloc(1,sizeof(struct char_stack)); . If you just simply say struct char_stack* stack= malloc(sizeof(struct char_stack); as you want only 1 item to save space and then I believe that it probably solve it. If it does not then I would suggest checking if you correctly pronounce sizeof(struct char_stack).In the end, you always must check if (stack==NULL) because the program might not find a space to allocate space for the pointer. Also, I would recommend using typedef struct char_stack Char_stack; so you don't need to write all the time the struct char_stack but only Char_stack . I hope that this will help you to find the problem.