Pointers to array of pointers in c -


can please explain me difference between 2 following declarations:

char (*arr_a)[5]; char arr_b[20];

and why:

sizeof (*arr_b) = sizeof (char) sizeof (*arr_a) = 5*sizeof(char) 

char (*arr_a)[5];

declares pointer 5-element array of char.

char arr_b[20];

declares 20-element array of char.

so, output of

sizeof (*arr_a)

should straight forward -- dereferencing pointer array yields array , it's size 5.

the following:

sizeof (*arr_b)

gives 1, because dereferencing identifier of array yields first element of array, of type char.

one thing need know understand how array evaluates in expression:

  • in most contexts, array evaluates pointer first element. example case when apply indexing array. a[i] synonymous *(a+i). array evaluates pointer, works expected.

  • there exceptions, notably sizeof, gives storage size of array itself. also, _alignof , & don't treat array pointer.


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