Using pointer after free()

Question

During my tests, I have found that it is possible to use pointer after free(). I have the following code:

typedef struct{

    int module_id;
    int adc_id;         


        

Answer 1

When you call free(phead), the memory phead points to is being freed, but the value of phead stays untouched, making the phead a dangling pointer. Accessing the memory that has already been freed produces undefined behavior.

It is a good practice to assign NULL to the pointer once you free the memory it points to:

free(phead);
phead = NULL;