Doubt related to free()

[sathishc58]

Hi All
I have a question related to free().

For example
A(char *buffer) call B(char *buffer)
B(char *buffer) in turn calls C(char *buffer)
C(char *buffer) in turn calls D(char *buffer)
D(char *buffer) in turn calls E(char *buffer)
and so on.........
I pass a pointer as a parameter from A()
A(char *buffer);
1) This buffer was freed somewhere in some function. (Deallocation could have done by B() or C() or D() or E() etc)
2) I did not set BUFFER=NULL after freeing up the buffer in any of the function.

Is there any way to know whether buffer was FREED or NOT when I return to A().
I believe BUFFER will be pointing to the location even if we free() the data.

Please let me know your response.

Thanks & Regards
Sathish Kumar

[JosAH]

Yep, the value of the buffer pointer isn't altered but it doesn't point to a valid memory region anymore; you have freed it so you can't use it anymore.

kind regards,

Jos

[gpraghuram]

Hi,
As Jos said it will be an invalid memory.
But if u want to find if there is a leak in code then go for Purify or boundschecker

raghu

[Tassos Souris]

You probably must get used to using pointer to pointers rather than pointers. For example when you have the head of a single linked list it is better to use that:

void freeList( struct List **head ){
    // Do the free of all the nodes here
    
    // Set it safely to NULL
    *head = NULL;
}

You must make it a rule that every free() is followed by a assignment to NULL:

free( ( void * )ptr );
ptr = NULL;