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cmallocdynamic-memory-allocationfreecalloc

A problem that is about calloc and free functions in C

I'm new in C.

Here is my code:

int *i = (int *)calloc(10, sizeof(int));
i[0] = 3;
i[1] = 1;
i[2] = 2;
i[3] = 5;
printf("before: %d %d %d %d\n", i[0], i[1], i[2], i[3]);
printf("before: %d %d\n", i, (i + 3));

free(i);

printf("after: %d %d %d %d\n", i[0], i[1], i[2], i[3]);
printf("after: %d %d\n", i, (i + 3));

and output: 

before: 3 1 2 5
before: 3 5
after: 0 0 2 5
after: 0 5

I used free() func. Why are not all elements of the array zero?

Solution

  • The data in memory maybe doesn't disappear, they can exist in the memory after freeing. But try to read from the freed memory is undefined behavior. To be sure, you can assign the pointer to NULL after freeing it (Setting variable to NULL after free).