Another useless C99 tidbit
From page 18 of the C99 standard:
All occurrences in a source file of the following sequences of three characters (called trigraph sequences) are replaced with the corresponding single character.
??= # ??( [ ??/ \ ??) ] ??' ^ ??< { ??! | ??> } ??- ~No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed above is not changed.
Ok, so take the following C program:
??=include <stdio.h> int main(int argc, char *argv??(??)) ??< printf("hello world\n"); ??>
And compile it with the -trigraphs switch to gcc:
dirac src $ gcc -trigraphs -o trigraphs trigraphs.c dirac src $ ./trigraphs hello world
Combined with this you could seriously obfuscate your C code.
Hidden Gems in C99 (1)
After some late night reading of the C99 spec, I've found quite a few hidden gems. I'm going to start posting some of these. Since it's late, I'll just post a teaser.
On page 64 of the C99 standard it says:
In all aspects of the language, the six tokens
<: :> <% %> %: %:%:behave,respectively,the same as the six tokens
[ ] { } # ##except for their spelling.
Really? Then let's try this program:
%:include <stdio .h> int main(int argc, char *argv<::>) <% printf("hello world\n"); %>
Compile it an run it:
dirac src $ gcc main.c dirac src $ ./a.out hello world
Whaddaya know... I know, I know... useless. Wait for the next post then.
About this website
Most Popular
Posts
| M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|
| « Jun | ||||||
| 1 | 2 | 3 | 4 | 5 | ||
| 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| 13 | 14 | 15 | 16 | 17 | 18 | 19 |
| 20 | 21 | 22 | 23 | 24 | 25 | 26 |
| 27 | 28 | 29 | ||||
Latest Book Review
How We Know What Isn'T So by Thomas GilovichMy rating: 4 of 5 stars
This is an excellent book that discusses mental traps that prevent you from thinking clearly. If you don't know about the perils of seeing patterns where there are none, or how susceptible we all are to the confirmation bias, you need to read this book. Two other books also come to mind, "Bad Science" by Ben Goldacre, and "How to Think about Weird Things" by Schick and Vaughn. These three books overlap somewhat, but they will make you a better critical thinker.
View all my reviews