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From: Alf P. Steinbach on 11 Jun 2010 07:42 * Martin B., on 11.06.2010 13:34: > > The constructing order of the specific constructor is relevant, and > *not* the declaration order of the members. (Or so I thought.) This will probably trigger a flood of like responses (one case where a mod factoid could be beneficial?), but in case it doesn't trigger that flood: no, the memory initializer list order does not matter, it's only the declaration order that matters. { Yes, a mod factoid could certainly have been beneficial. :) -mod/sk } Cheers, - Alf -- blog at <url: http://alfps.wordpress.com> [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Frank Bergemann on 11 Jun 2010 07:44 PolarPeter wrote: > One of many questions I typically ask candidates who come to interview > with me is this one: > > class A > { > public: > A() : y(2), x(y * 2) {} > ~A() {} > > private: > int x; > int y; > }; > > int main() > { > A a; > return 0; > } > > I ask them what the value of a.x and a.y will be after 'a' has been > constructed. > > [...] > > I'd like to know what you think - is it reasonable to expect > candidates who claim they have 10 years+ 'advanced' C++ experience to > know this? > I'd expect the candidate to say to you: "I see you have spent some efforts and not just quoted the example of Scott Meyer's 'Effective C++', Item #13 'List members in an initialization list in the order in which they are declared'." Likely you then would smile at each other :-) cheers, Frank -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Chris Morley on 12 Jun 2010 00:26 > I think it's a fair and reasonable question. For those who don't > get the correct answer a follow up question might be why is > x == 0 and y == 2. Go on, impress. Why? #include <stdio.h> class A { public: A() : y(2), x(y * 2) {} ~A() {} void print() {printf("x=%d, y=%d\n",x,y);} private: int x; int y; }; void testa() { A a; a.print(); } void foo() { int z=5; printf("%d\n",z); // ensure compiler doesn't optimise z away } int main() { foo(); testa(); return 0; } Compiled on VS2008 for win 32 console. Inline expansion set to keyword only (so we guarantee function calls & stack frames...) /O2 /Ob1 /Oi /GL /D "WIN32" /D "NDEBUG" /D "_CONSOLE" /D "_UNICODE" /D "UNICODE" /FD /EHsc /MD /Gy /Fo"Release\\" /Fd"Release\vc90.pdb" /W3 /nologo /c /Zi /TP /errorReport:prompt outputs: 5 x=10, y=2 x value is UB. I just seeded the stack in this example with 5 (on this platform). Seems a little harsh if they missed the first answer being UB to follow by asking a broken question... whose answer is "It's still UB." Chris -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: DeMarcus on 13 Jun 2010 05:45 On 2010-06-11 03:22, PolarPeter wrote: > One of many questions I typically ask candidates who come to interview > with me is this one: > > class A > { > public: > A() : y(2), x(y * 2) {} > ~A() {} > > private: > int x; > int y; > }; > > int main() > { > A a; > return 0; > } > > I ask them what the value of a.x and a.y will be after 'a' has been > constructed. > > Clearly, the issue here is that x is constructed first, and uses the > uninitialized value of y. However, a lot of candidates miss the order > issue, and think that a.y is 2, and a.x is 4. > > I think this question is pretty fundamental, given how often MILs are > used. I think people who say they have 10+ years professional > experience should be able either to see the issue, or at least talk > through why it works the way it works if they don't initially see it > but are then shown. > > I'd like to know what you think - is it reasonable to expect > candidates who claim they have 10 years+ 'advanced' C++ experience to > know this? > I would probably expect such person to know that there /is/ an initialization order mechanism for it. How it works takes no time to check up. However, since you ask; the most important thing is the way you present /yourself/ to a person that actually might be a really skilled programmer. If you judge him/her by one simple example only, he/she might think "Will this guy measure me by the number of lines I produce each day?". So as an answer to your question; well, yes, you could ask such question, but make sure you have a bunch of interesting questions or preferably a nice discussion where you could ask him/her something like "Tell me one of your most fun aha-experiences during your career". Or "What in C++0x are you waiting for most?". If you really want a 10 years+ experienced programmer it's important you don't make your company look boring. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Martin B. on 14 Jun 2010 18:03
Daniel Kr�gler wrote: > On 11 Jun., 13:34, "Martin B." <0xCDCDC...(a)gmx.at> wrote: >> PolarPeter wrote: >>> One of many questions I typically ask candidates who come to interview >>> with me is this one: >>> class A >>> { >>> public: >>> A() : y(2), x(y * 2) {} >>> ~A() {} >>> private: >>> int x; >>> int y; >>> }; >>> int main() >>> { >>> A a; >>> return 0; >>> } >>> I ask them what the value of a.x and a.y will be after 'a' has been >>> constructed. >>> Clearly, the issue here is that x is constructed first, and uses the >>> uninitialized value of y. However, a lot of candidates miss the order >>> issue, and think that a.y is 2, and a.x is 4. >> Under MSVC 2005 this give the result of y=2 and x=4. (With Language >> extensions disabled and with /W4 which doesn't give any warnings.) >> >> The constructing order of the specific constructor is relevant, and >> *not* the declaration order of the members. (Or so I thought.) > > You are misinformed. It is very important that the rules are as they > are specified, (...) Rather I'd say I was misremembering. Which just goes to show that the important part to remember is: Don't do this, or as item 47[*] says: "Define and initialize member variables in the same order." (Which also goes to show, that I could have just looked it up in the book sitting next to my desk -- if I'd remembered where I last read about it.) > On Jun 10, 9:22 pm, PolarPeter <polarpeterb...(a)gmail.com> wrote: >> I'd like to know what you think - is it reasonable to expect >> candidates who claim they have 10 years+ 'advanced' C++ experience to >> know this? Well I'm a C++ programmer with 5 years experience. Judge yourself how I handled the question. :-) cheers, Martin [*] Suttner/Alexandrescu, C++ Coding standards -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] |