Why freed struct in C still has data?

Question

When I run this code:

#include 

typedef struct _Food
{
    char          name [128];
} Food;

int
main (int argc, char **argv)
{
    Food  *f         


        

Answer 1

There's no such thing as "struct has data" or "struct doesn't have data" in C. In your program you have a pointer that points somewhere in memory. As long as this memory belongs to your application (i.e. not returned to the system) it will always contain something. That "something" might be total garbage, or it might look more or less meaningful. Moreover, memory might contain garbage that appears as something meaningful (remains of the data previously stored there).

This is exactly what you observe in your experiment. Once you deallocated the struct, the memory formerly occupied by it officially contains garbage. However, that garbage might still resemble bits and pieces of the original data stored in that struct object at the moment it was deallocated. In your case you got lucky, so the data looks intact. Don't count on it though - next time it might get totally destroyed.

As far as C language is concerned, what you are doing constitutes undefined behavior. You are not allowed to check whether a deallocated struct "has data" or not. The "why" question you are asking does not really exist in the realm of C language.