Question

I’m sure it doesn’t, but maybe there’s black magic in it, so here’s my question:

If I have a struct like this:

struct mystr {
    char * strp,
    unsigned int foo,
};

and I allocate memory for it and want to release it later. Do I have to do

free(mystr_var->strp);
free(mystr_var);

or is the last line enought, does the free() function follow the pointers and free them two?

Answer 1

Every individually allocated block of memory must be freed individually. free() will only free the memory block that the pointer points to and its has no knowledge of what is the content of that memory.

Hence, in your case you are doing it the right way by first freeing the innermost memory allocated in a structure and finally freeing the struct pointer.

If you just do free on the struct pointer, the struct memory gets freed. The memory held by char* strp, becomes a memory leak in your program lifetime.