C Programming | Difference Between Array and Pointer Variable Size with Example | 04
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design lecture, An array is a fixed-length collection of objects, which are stored sequentially in memory. There are only three things you can do with an array: sizeof - get its size You can apply sizeof to it. An array x of N elements of type T (T x[N]) has the size N * sizeof (T), which is what you should expect. For example, if sizeof (int) == 2 and int arr[5];, then sizeof arr == 10 == 5 * 2 == 5 * sizeof (int).
& - get its address You can take its address with &, which results in a pointer to the entire array.
any other use - implicit pointer conversion Any other use of an array results in a pointer to the first array element (the array "decays" to a pointer).That's all. Yes, this means arrays don't provide direct access to their contents. More specifically, there is no array indexing operator. Pointers A pointer is a value that refers to another object (or function). You might say it contains the object's address. Here are the operations that pointers support: sizeof - get its size
Like arrays, pointers have a size that can be obtained with sizeof. Note that different pointer types can have different sizes.
& - get its address
Assuming your pointer is an lvalue, you can take its address with &. The result is a pointer to a pointer.
- dereference it
Assuming the base type of your pointer isn't an incomplete type, you can dereference it; i.e., you can follow the pointer and get the object it refers to. Incomplete types include void and predeclared struct types that haven't been defined yet.
+, - - pointer arithmetic
If you have a pointer to an array element, you can add an integer amount to it. This amount can be negative, and ptr - n is equivalent to ptr + -n (and -n + ptr, since + is commutative, even with pointers). If ptr is a pointer to the i'th element of an array, then ptr + n is a pointer to the (i + n)'th array element, unless i + n is negative or greater than the number of array elements, in which case the results are undefined. If i + n is equal to the number of elements, the result is a pointer that must not be dereferenced.
That's it, really. However, there are a few other pointer operations defined in terms of the above fundamental operations:
struct dereference
p arrow m is equivalent to (*p).m, where . is the struct/union member access operator. This means p must be a pointer to a struct or union.
[] - indexed dereference
a[b] is equivalent to *(a + b). This means a and b must be a pointer to an array element and an integer; not necessarily respectively, because a[b] == *(a + b) == *(b + a) == b[a]. Another important equivalence is p[0] == 0[p] == *p.