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| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stddef.h>
enum { SIZE = 32 };
void func(void) {
int nums[SIZE];
int end;
int *next_num_ptr = nums;
size_t free_byteselements;
/* Increment next_num_ptr as array fills */
free_byteselements = &end - next_num_ptr;
} |
This program incorrectly assumes that the nums array is adjacent to the end variable in memory. A compiler is permitted to insert padding bits between these two variables, or even reorder them in memory.
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| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stddef.h>
enum { SIZE = 32 };
void func(void) {
int nums[SIZE];
int *next_num_ptr = nums;
size_t free_byteselements;
/* Increment next_num_ptr as array fills */
free_byteselements = (&(nums[SIZE]) - next_num_ptr) * sizeof(int);
} |
Exceptions
ARR36-EX1: Comparing two pointers within the same object is allowed.
ARR36-EX2: Subtracting two pointers to char within the same object is allowed.
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