6 ms·

trigraphs are removed in c++ 17 https://en.m.wikipedia.org/wiki/C%2B%2B17#Removed_features https://en.m.wikipedia.org/wiki/C%2B%2B17#Removed_features

amelius 4y ago
I've never seen them used anywhere.
- Rebelgecko 4y ago
  They're good for obfuscating source code but AFAICT that's about it on modern machines
  - sargstuff 4y ago
    Less obscure if physical print type head doesn't have the corresponding trigraph representation. Unicode is a worthy successor to trigraphs -- no need for pre-processing! Guess with tri-graph elimination & awk getting unicode support will have to gawk C with cpp using pipology theory. But think the cpp has to go away first, after enough sed. https://grayson.sh/blogs/using-piphilology-to-hide-strings https://grayson.sh/blogs/using-piphilology-to-hide-strings https://www.gnu.org/software/gawk/manual/gawk.html#Signature-Program https://www.gnu.org/software/gawk/manual/gawk.html#Signature...
- mfost 4y ago
  They were meant for coding C on machines that had even less than ASCII as available text encoding really. So no wonder you never see them.
- shakna 4y ago
  They were meant, mostly, for punch-card machines. So if you started programming anywhere after the point in time when you needed to hand off your code to a punch card operator, you're unlikely to have seen them.
  - WalterBright 4y ago
    They were meant to support EBCDIC.
pjmlp 4y ago
They are still around in C though.
- david2ndaccount 4y ago
  They are being removed in C23.
  - pjmlp 4y ago
    I see, thanks.
- KerrAvon 4y ago
  gone in C23
  - sargstuff 4y ago
    ... but if someone sed it back in .....
  - pjmlp 4y ago
    I see, thanks.
piesquaredarr 4y ago
Huh, I never realized that C++ standards were removing C features. Time to be more careful about using g++ for everything.
- Denvercoder9 4y ago
  C++ has never been a strict superset of C. The most obvious example is the "class" and "new" keywords which can be used as an identifier in C, but not in C++. There's more subtle differences as well, such as character literals having type int in C and char in C++.
  - wheels 4y ago
    Another really common one is that casting from void * to any other type doesn't require a cast in C, but it does in C++: #include <stdlib.h> int main() { int *foo = malloc(sizeof(int)); return 0; } That works in C, but not in C++. There's actually another subtle different in there that main() means "unspecified arguments" in C, and "no arguments" in C++. ("No arguments" in C would be main(void).) However, it's no longer commonly used that way in C, but casts from void * to other types is very common in C.
    - favorited 4y ago
      The `func()` vs `func(void)` difference has been deprecated for a while, and is removed in C23.
  - bee_rider 4y ago
    Ah, what an elegant example, haha.
  - tialaramex 4y ago
    Using unions for type punning is legal C, but the exact same code has UB in C++ The modern C++ way to do this ~safely isn't legal C, and yet the type pun isn't safe in C++. I believe using memcpy() to launder the bits is legal in both languages and in some cases your compiler can figure out what you're doing and not actually emit the unnecessary copy.

amelius 4y ago

I've never seen them used anywhere.

Rebelgecko 4y ago
They're good for obfuscating source code but AFAICT that's about it on modern machines
- sargstuff 4y ago
  Less obscure if physical print type head doesn't have the corresponding trigraph representation. Unicode is a worthy successor to trigraphs -- no need for pre-processing! Guess with tri-graph elimination & awk getting unicode support will have to gawk C with cpp using pipology theory. But think the cpp has to go away first, after enough sed. https://grayson.sh/blogs/using-piphilology-to-hide-strings https://grayson.sh/blogs/using-piphilology-to-hide-strings https://www.gnu.org/software/gawk/manual/gawk.html#Signature-Program https://www.gnu.org/software/gawk/manual/gawk.html#Signature...
mfost 4y ago
They were meant for coding C on machines that had even less than ASCII as available text encoding really. So no wonder you never see them.
shakna 4y ago
They were meant, mostly, for punch-card machines. So if you started programming anywhere after the point in time when you needed to hand off your code to a punch card operator, you're unlikely to have seen them.
- WalterBright 4y ago
  They were meant to support EBCDIC.

pjmlp 4y ago

They are still around in C though.

david2ndaccount 4y ago
They are being removed in C23.
- pjmlp 4y ago
  I see, thanks.
KerrAvon 4y ago
gone in C23
- sargstuff 4y ago
  ... but if someone sed it back in .....
- pjmlp 4y ago
  I see, thanks.

piesquaredarr 4y ago

Huh, I never realized that C++ standards were removing C features. Time to be more careful about using g++ for everything.

Denvercoder9 4y ago
C++ has never been a strict superset of C. The most obvious example is the "class" and "new" keywords which can be used as an identifier in C, but not in C++. There's more subtle differences as well, such as character literals having type int in C and char in C++.
- wheels 4y ago
  Another really common one is that casting from void * to any other type doesn't require a cast in C, but it does in C++: #include <stdlib.h> int main() { int *foo = malloc(sizeof(int)); return 0; } That works in C, but not in C++. There's actually another subtle different in there that main() means "unspecified arguments" in C, and "no arguments" in C++. ("No arguments" in C would be main(void).) However, it's no longer commonly used that way in C, but casts from void * to other types is very common in C.
  - favorited 4y ago
    The `func()` vs `func(void)` difference has been deprecated for a while, and is removed in C23.
- bee_rider 4y ago
  Ah, what an elegant example, haha.
- tialaramex 4y ago
  Using unions for type punning is legal C, but the exact same code has UB in C++ The modern C++ way to do this ~safely isn't legal C, and yet the type pun isn't safe in C++. I believe using memcpy() to launder the bits is legal in both languages and in some cases your compiler can figure out what you're doing and not actually emit the unnecessary copy.