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.
