Interesting C Question

ar1 · 05-07-2005, 04:53 AM

Take a look at the following code:

Code:

char a[10] = "abcdefghi";
printf("%s", a[3]);
printf("%s", 3[a]);

Both the printf's give the same output. Why??

It must be something to do with the way the string is represented in the memory by the C compiler, but what is it?

I would have thought that the offset is multiplied by the size of char, in which case they should give different outputs :/

nukkel · 05-07-2005, 05:47 AM

Yes this is quite cool...

In C,

Code:

x[\i]

is equivalent to

Code:

*(x + i)

, and because of the commutativity (is this the right word in English???) of the addition this is also equivalent to

Code:

*(i + x)

which in turn can also be written as

Code:

i[x]

...

Quote:

Originally posted by ar1
I would have thought that the offset is multiplied by the size of char, in which case they should give different outputs :/ [/B]

sizeof (char) = 1, so that makes no difference here.

greets,
nukkel

jtshaw · 05-07-2005, 10:24 AM

The size of the type actually shouldn't matter in this case. Pointers in C are always the same size, regardless of the datatype they are pointing too.