How to find the size of integer array

Question

How to find the size of an integer array in C.

Any method available without traversing the whole array once, to find out the size of the array.

Answer 1

If array is static allocated:

size_t size = sizeof(arr) / sizeof(int);

if array is dynamic allocated(heap):

int *arr = malloc(sizeof(int) * size);

where variable size is a dimension of the arr.

Answer 2

If the array is a global, static, or automatic variable (int array[10];), then sizeof(array)/sizeof(array[0]) works.

If it is a dynamically allocated array (int* array = malloc(sizeof(int)*10);) or passed as a function argument (void f(int array[])), then you cannot find its size at run-time. You will have to store the size somewhere.
Note that sizeof(array)/sizeof(array[0]) compiles just fine even for the second case, but it will silently produce the wrong result.

Answer 3

_msize(array) in Windows or malloc_usable_size(array) in Linux should work for the dynamic array

Both are located within malloc.h and both return a size_t

Answer 4

int len=sizeof(array)/sizeof(int);

Should work.