4 ms·

Pointers aren't even there for supporting a legacy language, they have their use and are distinct from references. Mixing the two and thinking they are equivale

Pointers aren't even there for supporting a legacy language, they have their use and are distinct from references. Mixing the two and thinking they are equivalent (though they are close in what they do) is a mistake.

throwawayaway 12y ago
How can you have pointers without allowing all the holes that C allows?
- pjmlp 12y ago
  By using them like safe system programming languages from Algol/Mesa line do. Out function parameters are implicit pointers via references. Cannot be null. Pointers and arrays aren't compatible. Pointer arithmetic is frown upon and in many of those languages requires an explicit unsafe block/system module import.
  - throwawayaway 12y ago
    would it be fair to say you have just described references, or do I have to go and lookup this algol/mesa stuff?
    - pjmlp 12y ago
      I can provide a better example, but only tonight. At work now.
    - pjmlp 12y ago
      Some examples using Modula-2, a Mesa's successor. How it allows for all the C pointer features, while adding a little bit more safety. MODULE examples; IMPORT Terminal, SYSTEM; (* procedure with reference parameter, no need for pointers *) PROCEDURE ChangeParam (VAR changeMe: CARDINAL); BEGIN changeMe := 25; END ChangeParam; (* procedure with a slice, bounds given by HIGH(changeMe) and LOW(changeMe). also a string in this case no need for explicit pointers *) PROCEDURE DumpLetters (VAR letters: ARRAY OF CHAR); VAR i : CARDINAL; BEGIN FOR i := 0 TO HIGH(letters) DO WriteChar(letters[i]); WriteLn; (* Or just use *) WriteString (letters); END DumpLetters; VAR anInt : CARDINAL := 12 ; aPtr : POINTER TO CHAR; aBuffer : ARRAY [1..2] OF CHAR; anAddr : ADDRESS; (* think void* *) aPtr2 : POINTER TO CHAR; BEGIN WriteInt(anInt); (* writes 12 *) ChangeParam (anInt); WriteInt(anInt); (* writes 25 *) DumpLetters ('A simple string'); NEW(aPtr); (* The compiler knows the size, no need for sizeof, but you can use ALLOCATE(aPTR, SIZE(CHAR)) if you want *) (* This is where it shares the same problems with C, due to manual memory control *) DISPOSE(aPtr); (* do pointer arithmetic if really required *) anAddr := SYSTEM.ADDADR (SYSTEM.ADR(aBuffer), SIZE(CHAR) * 1); aPtr2 := SYSTEM.CAST(POINTER TO CHAR, anAddr); (* aPtr2 now points to aBuffer(2) *) END examples; So the compiler will mark this module as unsafe since the meta-package SYSTEM is being used. All Modula-2 successors, have GC support, as such the DISPOSE() would have to be written as SYSTEM.DISPOSE() and could only be applied to untraced pointers.
      - throwawayaway 12y ago
        very interesting, reminds me of this: http://stackoverflow.com/questions/6456253/why-is-reference-to-array-defined-in-such-confusing-way-in-c http://stackoverflow.com/questions/6456253/why-is-reference-... it's a great shame it's defined in such an alien to use way in C++.
- Ragnarork 12y ago
  By not using them like in C. Of course this isn't an argument, but this shows that even though C++ doesn't prevent you from falling into the same trap that are present in C, it does give you the tool to at least allow you to do better than C to avoid these traps, notably thanks to RAII. Oh and let's not forget nullptr, which is a blessing compared to NULL. Pointers are still a feature of both languages. Pointers in C++ are basically the same than in C, just with mechanisms that solve the ownership and some safety problems. So yes, it allows the same holes, but at least you have tools to avoid falling in them.
  - throwawayaway 12y ago
    You need to understand so much about C to even talk about pointers in C++, and everything related to them, it's not funny. RAII -> Why? nullptr vs. NULL -> Why? Pointers -> Why? Don't use them in a certain way -> Why? The answer in all cases is C.
    - pjmlp 12y ago
      No, they are C++ pointers. There are endless languages that have pointers, no need to talk anything about C.
    - coldtea 12y ago
      >The answer in all cases is C. Starting to sound like a broken record. No, the answer in all cases can also be found in C++, and understood in C++ terms alone. C++ is a SUPERSET of C, not just an arbitrary language + C.
      - throwawayaway 12y ago
        cheers for the broken record warning. i will now abstain from further conversation - i will leave you with this - i don't care to read your answer in case i have to respond and you might have to deal with some more repetition: using the language of sets, the set of C++ minus the set of C, with what is now left: how can you explain the things i have listed?

throwawayaway 12y ago

How can you have pointers without allowing all the holes that C allows?

pjmlp 12y ago
By using them like safe system programming languages from Algol/Mesa line do. Out function parameters are implicit pointers via references. Cannot be null. Pointers and arrays aren't compatible. Pointer arithmetic is frown upon and in many of those languages requires an explicit unsafe block/system module import.
- throwawayaway 12y ago
  would it be fair to say you have just described references, or do I have to go and lookup this algol/mesa stuff?
  - pjmlp 12y ago
    I can provide a better example, but only tonight. At work now.
  - pjmlp 12y ago
    Some examples using Modula-2, a Mesa's successor. How it allows for all the C pointer features, while adding a little bit more safety. MODULE examples; IMPORT Terminal, SYSTEM; (* procedure with reference parameter, no need for pointers *) PROCEDURE ChangeParam (VAR changeMe: CARDINAL); BEGIN changeMe := 25; END ChangeParam; (* procedure with a slice, bounds given by HIGH(changeMe) and LOW(changeMe). also a string in this case no need for explicit pointers *) PROCEDURE DumpLetters (VAR letters: ARRAY OF CHAR); VAR i : CARDINAL; BEGIN FOR i := 0 TO HIGH(letters) DO WriteChar(letters[i]); WriteLn; (* Or just use *) WriteString (letters); END DumpLetters; VAR anInt : CARDINAL := 12 ; aPtr : POINTER TO CHAR; aBuffer : ARRAY [1..2] OF CHAR; anAddr : ADDRESS; (* think void* *) aPtr2 : POINTER TO CHAR; BEGIN WriteInt(anInt); (* writes 12 *) ChangeParam (anInt); WriteInt(anInt); (* writes 25 *) DumpLetters ('A simple string'); NEW(aPtr); (* The compiler knows the size, no need for sizeof, but you can use ALLOCATE(aPTR, SIZE(CHAR)) if you want *) (* This is where it shares the same problems with C, due to manual memory control *) DISPOSE(aPtr); (* do pointer arithmetic if really required *) anAddr := SYSTEM.ADDADR (SYSTEM.ADR(aBuffer), SIZE(CHAR) * 1); aPtr2 := SYSTEM.CAST(POINTER TO CHAR, anAddr); (* aPtr2 now points to aBuffer(2) *) END examples; So the compiler will mark this module as unsafe since the meta-package SYSTEM is being used. All Modula-2 successors, have GC support, as such the DISPOSE() would have to be written as SYSTEM.DISPOSE() and could only be applied to untraced pointers.
    - throwawayaway 12y ago
      very interesting, reminds me of this: http://stackoverflow.com/questions/6456253/why-is-reference-to-array-defined-in-such-confusing-way-in-c http://stackoverflow.com/questions/6456253/why-is-reference-... it's a great shame it's defined in such an alien to use way in C++.
Ragnarork 12y ago
By not using them like in C. Of course this isn't an argument, but this shows that even though C++ doesn't prevent you from falling into the same trap that are present in C, it does give you the tool to at least allow you to do better than C to avoid these traps, notably thanks to RAII. Oh and let's not forget nullptr, which is a blessing compared to NULL. Pointers are still a feature of both languages. Pointers in C++ are basically the same than in C, just with mechanisms that solve the ownership and some safety problems. So yes, it allows the same holes, but at least you have tools to avoid falling in them.
- throwawayaway 12y ago
  You need to understand so much about C to even talk about pointers in C++, and everything related to them, it's not funny. RAII -> Why? nullptr vs. NULL -> Why? Pointers -> Why? Don't use them in a certain way -> Why? The answer in all cases is C.
  - pjmlp 12y ago
    No, they are C++ pointers. There are endless languages that have pointers, no need to talk anything about C.
  - coldtea 12y ago
    >The answer in all cases is C. Starting to sound like a broken record. No, the answer in all cases can also be found in C++, and understood in C++ terms alone. C++ is a SUPERSET of C, not just an arbitrary language + C.
    - throwawayaway 12y ago
      cheers for the broken record warning. i will now abstain from further conversation - i will leave you with this - i don't care to read your answer in case i have to respond and you might have to deal with some more repetition: using the language of sets, the set of C++ minus the set of C, with what is now left: how can you explain the things i have listed?