In <[🔎] 200906171954.59429.v13@v13.gr>, Stefanos Harhalakis wrote:
>On Wednesday 17 June 2009, Boyd Stephen Smith Jr. wrote:
>> In <[🔎] 200906171857.57749.v13@v13.gr>, Stefanos Harhalakis wrote:
>> >Same thing for the trigraphs.
>>
>> puts("What??!"); /* ;) */
>
>I meant that they are not very popular and that they are not covered in
> most books or tutorials.
I know. I was attempting to make a joke by misusing a trigraph. (Per the
standard that would output "What|\n".)
> Thus, it is not obvious that this:
>
>#include<stdio.h>
>int main() { printf("??!??/n"); }
>
>may not output what the user expects (depending on the compiler)
Agreed.
>or why this:
>
>#include <stdio.h>
>int main() { printf("%c\n", "123"<:2:>); }
>
>will properly compile and output "3"
Those aren't trigraphs. They aren't substituted during phase 1 of
translation. They are only recognized as independent tokens, never (e.g.)
inside a string literal. They also stringify differently than the tokens
they can be substituted for.
Different stringification:
#define str(x) #x
int main() { puts(str(??!)); puts(str(<:)); }
outputs "|\n<:\n" not "|\n[\n".
Parsed after phase 1:
#define gltk(x, y) x ## y
#define str(x) # x
#define estr(x) str(x)
int main() { puts("??" "!" gtk2(<, :) 1 gtk2(:, >)); }
outputs "?!\n", not "\n".
(GCC pukes on it saying ":>" and "<:" are not preprocessing tokens, but
that's non-conformant per 6.4.1.)
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@iguanasuicide.net ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/
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