使用C中的结构的malloc遍历内存块

Question

I am unsure how to index through one contiguous chunk of dynamically allocated memory.

typedef struct p
{
    char name[30];
    int age;
} Person;

...in main

//Create enough memory to hold 20 'Person's
Person *people = (Person *)malloc(sizeof(Person) * 20);

How can I index through this to set variables name and age of each person? Given that file has proper layout.

I attempted the following, but after a couple iterations, I got a segfault.

int i;
for (i = 0; i < 20; i++) {
    fscanf(file, "%s", (people + (i * sizeof(Person)))->name);
    fscanf(file, "%d", &((people + (i * sizeof(Person)))->age));
}    

Is there a way to index using '[x]'?

Thank you

Answer 1

I think the confusion here is about how pointer arithmetic works.

When you add x to a pointer of type T* , it doesn't add x to the base pointer but x * sizeof(T) . (With exception to void* . Pointer arithmetic is undefined on void* )

So, to fix your case you can use (people + i) instead of (people + i* sizeof(..))

Another way of doing it would be to use - people[i] .

Memory pointed to by pointers can be indexed into just like arrays of the same type.

I hope this clears the confusion.