Fun with pointers in C++
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Sorry, that's not my code, an i cant change it. I just saw it in some code and where surprised what's that :D Returning references would make it much harder to read:
GetA() = GetB()
looks like What the hell? Assignment to a Function? :omg: :wtf:
Learn to read code. Assignment to a function would be
GetA = GetB()
which would mean GetB() returns a function pointer rather than an int* and GetA is function pointer rather than a function. Learn to read code.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
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Your code will be correct if both GetA and GetB return pointer on GLOBAL or STATIC variable same type ofcorse. It is possible to code on C++ without C-knowledge, but not to programm :cool:
It would also be correct within the context of the code for a class where the functions are returning pointers to data members.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
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My only problem with that is that GetA and GetB are being called twice each. There is, of course, no guarantee that the second call to either will return the same value as the first. Further, there is not guarantee that either isn't an expensive operation. I would probably go for the much clearer: A* pa = GetA(); B* pb = GetB(); if (pa != NULL && pb!= NULL) *pa = *pb; Unfortunately, this method would always call GetB once, while the original would never call GetB if the first call to GetA returned NULL, so determining which is more efficient depends of how expensive the call to GetB is, and the likelihood than GetA returns null. Which would give us this: A* pa = GetA(); if (pa != NULL) { B* pb = GetB(); if (pb != NULL) *pa = *pb; } Which, despite being the most keystrokes, would be the best method in terms of speed efficiency, memory efficiency (fewest assembly instructions), and code clarity. In other words, just freakin' learn to type.
Truth, James
what about:
int* a;
int* b;
if ((a = GetA()) && (b = GetB()))
{
*a = *b;
}#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
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what about:
int* a;
int* b;
if ((a = GetA()) && (b = GetB()))
{
*a = *b;
}#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
That does work, but
if (a = GetA()) ...
is too easy to mistake for
if (a == GetA()) ...
Which is why I never leave the comparison implied, so we get:
if ((a = GetA()) != NULL && (b = GetB()) != NULL)
which is rather unwieldy. And for what purpose? The longer version I posted will produce the exact same object code.
Truth, James
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That does work, but
if (a = GetA()) ...
is too easy to mistake for
if (a == GetA()) ...
Which is why I never leave the comparison implied, so we get:
if ((a = GetA()) != NULL && (b = GetB()) != NULL)
which is rather unwieldy. And for what purpose? The longer version I posted will produce the exact same object code.
Truth, James
James Curran wrote:
The longer version I posted will produce the exact same object code.
Will it? The version you and I just discussed has the advantage of short-circuiting, where the first version you posted does not. Which is a "limitation" you pointed-out.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
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James Curran wrote:
The longer version I posted will produce the exact same object code.
Will it? The version you and I just discussed has the advantage of short-circuiting, where the first version you posted does not. Which is a "limitation" you pointed-out.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
I was referring to the second version I posted (i.e., "the longer version", the one with nested if()s). And that does produce identical object code. From VisualStudio 2013, Release build: Mine:
; 21 : void Method2()
; 22 : {
; 23 : A* pa = GetA();00023 e8 00 00 00 00 call ?GetA@@YAPAHXZ ; GetA
00028 8b f0 mov esi, eax; 24 : if (pa != NULL)
0002a 85 f6 test esi, esi
0002c 74 0d je SHORT $LN6@wmain; 25 : {
; 26 : B* pb = GetB();0002e e8 00 00 00 00 call ?GetB@@YAPAHXZ ; GetB
; 27 : if (pb != NULL)
00033 85 c0 test eax, eax
00035 74 04 je SHORT $LN6@wmain; 28 : *pa = *pb;
00037 8b 08 mov ecx, DWORD PTR [eax]
00039 89 0e mov DWORD PTR [esi], ecx
$LN6@wmain:; 29 : }
; 30 : }and yours:
; 32 : void Method3()
; 33 : {
; 34 : A* a;
; 35 : B* b;
; 36 : if ((a = GetA()) && (b = GetB()))0003b e8 00 00 00 00 call ?GetA@@YAPAHXZ ; GetA
00040 8b f0 mov esi, eax
00042 85 f6 test esi, esi
00044 74 0d je SHORT $LN13@wmain
00046 e8 00 00 00 00 call ?GetB@@YAPAHXZ ; GetB
0004b 85 c0 test eax, eax
0004d 74 04 je SHORT $LN13@wmain; 37 : {
; 38 : *a = *b;0004f 8b 08 mov ecx, DWORD PTR [eax]
00051 89 0e mov DWORD PTR [esi], ecx
$LN13@wmain:That's with all standard "Release mode" optimizations on, except "Whole Program Optimization" (to prevent it from inlining GetA & GetB)
Truth, James
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I was referring to the second version I posted (i.e., "the longer version", the one with nested if()s). And that does produce identical object code. From VisualStudio 2013, Release build: Mine:
; 21 : void Method2()
; 22 : {
; 23 : A* pa = GetA();00023 e8 00 00 00 00 call ?GetA@@YAPAHXZ ; GetA
00028 8b f0 mov esi, eax; 24 : if (pa != NULL)
0002a 85 f6 test esi, esi
0002c 74 0d je SHORT $LN6@wmain; 25 : {
; 26 : B* pb = GetB();0002e e8 00 00 00 00 call ?GetB@@YAPAHXZ ; GetB
; 27 : if (pb != NULL)
00033 85 c0 test eax, eax
00035 74 04 je SHORT $LN6@wmain; 28 : *pa = *pb;
00037 8b 08 mov ecx, DWORD PTR [eax]
00039 89 0e mov DWORD PTR [esi], ecx
$LN6@wmain:; 29 : }
; 30 : }and yours:
; 32 : void Method3()
; 33 : {
; 34 : A* a;
; 35 : B* b;
; 36 : if ((a = GetA()) && (b = GetB()))0003b e8 00 00 00 00 call ?GetA@@YAPAHXZ ; GetA
00040 8b f0 mov esi, eax
00042 85 f6 test esi, esi
00044 74 0d je SHORT $LN13@wmain
00046 e8 00 00 00 00 call ?GetB@@YAPAHXZ ; GetB
0004b 85 c0 test eax, eax
0004d 74 04 je SHORT $LN13@wmain; 37 : {
; 38 : *a = *b;0004f 8b 08 mov ecx, DWORD PTR [eax]
00051 89 0e mov DWORD PTR [esi], ecx
$LN13@wmain:That's with all standard "Release mode" optimizations on, except "Whole Program Optimization" (to prevent it from inlining GetA & GetB)
Truth, James
Interesting. Thanks.
#SupportHeForShe
If your actions inspire others to dream more, learn more, do more and become more, you are a leader.-John Q. Adams You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun Only 2 things are infinite, the universe and human stupidity, and I'm not sure about the former.-Albert Einstein
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C3D1 wrote:
Returning references would make it much harder to read
We'll just have to agree to disagree on that. IMO, this is a quite useful C++ paradigm.
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
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Daniel Pfeffer wrote:
IMO, this is a quite useful C++ paradigm.
...and that makes me even happier to barely being able to read C++ :laugh:
De gustibus non est disputandum :)
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
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De gustibus non est disputandum :)
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
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That's what I like about this forum. You go in thinking programming and you get a bit of Latin training. Hope I remember what the phrase means next time I see it.
Me too. There are plenty of sites around that merely answer programming questions, but only a few with the range of highly intelligent, humorous, and opinionated contributors that you find here. Amazingly, the amount of sniping and backbiting is kept to a minimum! Long may it last!
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
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Me too. There are plenty of sites around that merely answer programming questions, but only a few with the range of highly intelligent, humorous, and opinionated contributors that you find here. Amazingly, the amount of sniping and backbiting is kept to a minimum! Long may it last!
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
-
Me too. There are plenty of sites around that merely answer programming questions, but only a few with the range of highly intelligent, humorous, and opinionated contributors that you find here. Amazingly, the amount of sniping and backbiting is kept to a minimum! Long may it last!
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
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In two hours you can have a great lunch, jogging, some fun with your partner, some nice song listening/playing and also a shower. All that cannot be done because the language is cryptic: that's why I hate C/C++! Good post, though...
Mario Vernari wrote:
that's why I hate C/C++!
Yea, I kind of agree with that sentiment, however, I have yet to run across the language that will supply me with a great lunch, but I do admit to sometimes having fun with it. (Does that mean I'm cheating on my partner?)
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In two hours you can have a great lunch, jogging, some fun with your partner, some nice song listening/playing and also a shower. All that cannot be done because the language is cryptic: that's why I hate C/C++! Good post, though...
Mario Vernari wrote:
that's why I hate C/C++!
Yea, I kind of agree with that sentiment, however, I have yet to run across the language that will supply me with a great lunch, but I do admit to sometimes having fun with it. (Not C++ and does that mean I'm cheating on my partner?)
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De gustibus non est disputandum :)
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
Daniel Pfeffer wrote:
De gustibus non est disputandum :)
I.e. C++ is the Durian (stinkfruit) in Software Development.
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C3D1 wrote:
Returning references would make it much harder to read
We'll just have to agree to disagree on that. IMO, this is a quite useful C++ paradigm.
If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. --Winston Churchill
I agree, but I definitely would not name such a function "GetA".
"If you don't fail at least 90 percent of the time, you're not aiming high enough." Alan Kay.
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Sorry, that's not my code, an i cant change it. I just saw it in some code and where surprised what's that :D Returning references would make it much harder to read:
GetA() = GetB()
looks like What the hell? Assignment to a Function? :omg: :wtf:
You can't read C++ code without knowing the types. Who knows if equals was overridden, everything could happen. Even then you should read, GetA() return something, then operator = is called on this something.