Thread: array of pointers/pointer arithmetic

Originally Posted by itCbitC

imho by stepwise dissecting the expression *(*(a + 0) + 0) as in
a + 0 is a pointer to the first element of a ie a + 0 == &a[0].
*(a + 0) applies dereferencing to obtain a[0].
*(a + 0) + 0 points to the same place that a[0] is pointing to.

We were doing fine up to right here. *(a+0) is a character a[0], adding 0 to it gives us the same character.

Originally Posted by itCbitC

*(*(a + 0) + 0) accesses the object that a[0] is pointing to ie 'A' in this case.

And this is just an error.

Originally Posted by tabstop

We were doing fine up to right here. *(a+0) is a character a[0], adding 0 to it gives us the same character.

And this is just an error.

care to explain if you please what you mean by the above statement??

Originally Posted by itCbitC

care to explain if you please what you mean by the above statement??

What it means is that I can't read. We have an array of char *, not of char as I had originally read it. So yes what you said is what we have. Sorry.

ah ha! yes I had made the same mistake earlier

Indeed ItC... i think i was mixed up with the notation show at the bottom of this fragment:

Code:

char *a[2];
	char *b[2];
	char **all[2] = {a, b};
	a[0]= (char *)malloc(20);
	a[1]= (char *)malloc(20);
	b[0]= (char *)malloc(20);
	b[1]= (char *)malloc(20);

	*(a + 0) = "AEI";
	*(a + 1) = "OUY";

	printf("string: %s\n", a[0]);
	printf("string: %s\n", a[1]);
	printf("char: %c\n", *(*(a + 0) + 0));
	printf("char: %c\n", *(*(a + 0) + 1));
	printf("char: %c\n", *(*(a + 0) + 2));

	*(*(all + 1) + 0) = "DOG";
	*(*(all + 1) + 1) = "CAT";

	printf("string: %s\n", b[0]);
	printf("string: %s\n", b[1]);
	printf("char: %c\n", *(*(*(all + 1) + 0) + 0));
	printf("char: %c\n", *(*(*(all + 1) + 0) + 1));
	printf("char: %c\n", *(*(*(all + 1) + 0) + 2));
	printf("char: %c\n", *(*(*(all + 1) + 1) + 0));
	printf("char: %c\n", *(*(*(all + 1) + 1) + 1));
	printf("char: %c\n", *(*(*(all + 1) + 1) + 2));

Which Outputs:

string: AEI
string: OUY
char: A
char: E
char: I
string: DOG
string: CAT
char: D
char: O
char: G
char: C
char: A
char: T

Many hours later I have "completed" the main program with one annoying warning about passing non const data to const parameters...

Code:

int main()
{
void test(const char * const *[]);
char *a[MAX];
char *b[MAX];
char *c[MAX;
char **all[MAXMEMBER] = {a, b, c};
test(all);
}

void test(const char * const *total[])
{
; //modify individual characters or the string as a whole is an error... but still a warning
}

Which gives me a "passing argument 1 of ‘test’ from incompatible pointer type" in eclipse and a similar warning in gcc. I am thinking some kind of cast is appropriate here.