Can use pointer after free?

Yes, when you use a free(px); call, it frees the memory that was malloc’d earlier and pointed to by px. The pointer itself, however, will continue to exist and will still have the same address. It will not automatically be changed to NULL or anything else.

Can a pointer point to NULL?

Besides memory addresses, there is one additional value that a pointer can hold: a null value. A null value is a special value that means the pointer is not pointing at anything. A pointer holding a null value is called a null pointer.

What happens if u free a pointer twice?

Calling free() twice on the same value can lead to memory leak. When a program calls free() twice with the same argument, the program’s memory management data structures become corrupted and could allow a malicious user to write values in arbitrary memory spaces.

What happens if you free memory twice?

The heap manager may have since reallocated the memory your stale pointer is pointing to. Freeing it again is not the same as saying free(NULL) , and will result in undefined behavior. This is undefined behavior, that can result in heap corruption or other severe consequences.

Does free set pointer to NULL in C?

No. The free() function takes a pointer. In C functions arguments are passed by value. So the pointer passed to free() cannot be changed by the function.

How do you make a pointer null?

Any pointer that contains a valid memory address can be made as a NULL pointer by assigning 0. Example: Here, firstly ptr is initialized by the address of num, so it is not a NULL pointer, after that, we are assigning 0 to the ptr, and then it will become a NULL pointer.

Does C++ have null?

The C and C++ languages have a null character (NUL), a null pointer (NULL), and a null statement (just a semicolon (;)). The C NUL is a single character that compares equal to 0. The C NULL is a special reserved pointer value that does not point to any valid data object.

How do you check if the pointer is freed?

There is no reliable way to tell if a pointer has been freed, as Greg commented, the freed memory could be occupied by other irrelevant data and you’ll get wrong result. And indeed there is no standard way to check if a pointer is freed.