How to free a struct that contains only pointers

Question

I have a struct which you see below:

typedef struct _List {
    Person *person; // pointer for people list
    DoList *do; // Kinda timer, for checking list in some intervals
} List;

Are there any need to free this struct? If so, how can i free it?

Answer 1

You have to free the struct if you allocated it dynamically. You have to free its members before deallocating the struct if you allocated the members dynamically and don't have a reference to them anywhere else.

Here are some examples:

void freeNotRequiredHere() {
    List            nonDynamicList;
    Person          nonDynamicPerson;
    DoList          nonDynamicDoList;

    nonDynamicList.person = &nonDynamicPerson;
    nonDynamicList.do = &nonDynamicDoList;
}


void freeRequiredForStructListOnly() {
    List            *dynamicList;
    Person          nonDynamicPerson;
    DoList          nonDynamicDoList;

    dynamicList = (List *) malloc( sizeof(struct List) );

    dynamicList->person = &nonDynamicPerson;
    dynamicList->do = &nonDynamicDoList;

    free( dynamicList );
}


void freeRequiredForStructListAndPersonOnly() {
    List            *dynamicList;
    Person          *dynamicPerson;
    DoList          nonDynamicDoList;

    dynamicList = (List *) malloc( sizeof(struct List) );
    dynamicPerson = (Person *) malloc( sizeof(Person) );

    dynamicList->person = dynamicPerson;
    dynamicList->do = &nonDynamicDoList;

    free( dynamicPerson );
    free( dynamicList );
}


void freeRequiredForStructListAndPersonOnly( DoList *notSureDoList ) {
    List            *dynamicList;
    Person          *dynamicPerson;

    dynamicList = (List *) malloc( sizeof(struct List) );
    dynamicPerson = (Person *) malloc( sizeof(Person) );

    dynamicList->person = dynamicPerson;
    dynamicList->do = notSureDoList;

    // maybe notSureDoList was allocated with malloc(),
    // maybe it is a non-dynamic stack variable.
    // the calling function should deal with free()'ing notSureDoList

    free( dynamicPerson );
    free( dynamicList );
}