Question 4
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The program below has a problem. Which statement correctly describes it?
#include <stdio.h>
#include <stdlib.h>
int main(void) {
int *p = malloc(sizeof *p);
if (p == NULL)
return 1;
*p = 7;
free(p);
printf("%d\n", *p);
return 0;
}- A free(p) must come before *p = 7
- B The result of malloc() must be cast to (int *)
- C *p is read after free(p), when the memory no longer belongs to the program Correct
- D There is no error; it prints 7
Correct Answer: Option C
After free(p) the memory is returned to the allocator, so reading *p is a use-after-free – undefined behaviour. Use the value before freeing, then set p = NULL. (In C the cast on malloc() is not needed.)
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