I am writing a C based library and I'm a little confused when it comes to using free() to deallocate blocks of memory...
Essentially I have several similar structs defined this way:
typedef struct
{
pthread_t thread_id;
pthread_attr_t attr;
void *data;
size_t stacksize = NULL;
} thread_info;
Where I essentially use realloc() to allocate memory for this structure and have an array point to it.
My question is, if I use:
free(my_array[thread_index]);
Would the free() call deallocate memory used not just by the structure but all its data types within it, ie. the *thread_id*, attr, data, and stacksize will be deallocated as well or do I have to deallocate them individually then deallocate the structure from the array.
To me it would make sense that if I am using free() on such a structure all data contained within it will be deallocated and I wouldn't have to explicitly deallocate each struct attribute but I just want to make sure if that is the case.
For dynamically allocated "structures" (i.e. heirarchies of array's, struct's, etc), you need to call free on each pointer from "the bottom up". You can think of this operation as performing a depth-first traversal of a tree.
The usual restrictions apply to variables that are pointers to memory on the stack, rather than the heap. For example, variables defined with type[n], char[n] = 'abc', etc vs. allocations from the heap using the *alloc family of functions. Also beware of cases where there are multiple pointers to the same address, calling free twice on these is a programming error (though not necessarily a segmentation fault).