What is pointer Derefrencing in C?

Question

I was learning about recursion using c and there was a question with an array say for example:

void main(){
     char str[100];
     --snip--
     if(*str == 'c')
        count++;
     --snip--
}

here *str is the value retrieved from the pointer that points to first character of the string str.

My question is what is pointer derefrencing and can i do as follows:

--snip--
str+=1;
--snip--

to get new pointer pointing to the next location of another character in that string?

This may help too: https://stackoverflow.com/questions/1704407/what-is-the-difference-between-char-s-and-char-s — Jabberwocky, Mar 02 '21 at 09:23
*"can i do as follows"* - If you tried it, you would instantly notice that you cannot. — klutt, Mar 02 '21 at 09:43

mch · Answer 1 · 2021-03-02T09:23:33.270

5

You cannot increment an array, but you can increment a pointer to an element of the array:

char str[100];
char *pointer = str; //points to the begin
pointer++; //points to the second element
*pointer = 'a'; //sets the second element

str has the type char [100], in some expressions it decays to (e.g. behaves like) a pointer, but it is not a pointer, you cannot assign to str. str = ... or str+=1; is invalid, you can only assign something to an element of an array, not the array itself.

Therefore you have to create a pointer to an element of the array and then you can increment the pointer.

edited Mar 02 '21 at 09:23

answered Mar 02 '21 at 09:19

mch

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is that not same as str+=1 – Shoaib Wani Mar 02 '21 at 09:21
str is a pointer – Shoaib Wani Mar 02 '21 at 09:21
added some more text, is it better? An array is not a pointer – mch Mar 02 '21 at 09:27
in the book it does str+1 – Shoaib Wani Mar 02 '21 at 09:29
what will str+1 do anyways? – Shoaib Wani Mar 02 '21 at 09:29
`str+1` is different than `str+=1`. In `str+1` `str` decays to a pointer and then `1` gets added, so `str+1` points to the second element, but it does not change `str`. – mch Mar 02 '21 at 09:31
now i understand it thanks! – Shoaib Wani Mar 03 '21 at 10:26

What is pointer Derefrencing in C?

1 Answers1