C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How to judge whether an inline function is inlined or not          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message hzhuo1@gmail.com Guest Posted: Sun Jul 23, 2006 2:53 pm    Post subject: How to judge whether an inline function is inlined or not ===================================== MODERATOR'S COMMENT: Let's keep replies on-topic: What the Standard says or should say about function ininling. ===================================== END OF MODERATOR'S COMMENT It is well known that a function can be explicitly declared inline using the keyword "inline". But the compiler doesn't make sure the inline function is really inlined. For example, in the following code, the function f is declared inline, but how can we judge whether the compiler substitudes the function call with its implementation code, or just give a function call？ I will be appreciative if anyone can give some suggestions. Zhuo Hao July 23rd,2006 The code is as follows: #include<iostream> using namespace std; inline void f(){ cout<<"Hello"; cout<<" World!"<<endl; } int main(){ f(); return 1; } --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Guest Posted: Sun Jul 23, 2006 6:45 pm    Post subject: Re: How to judge whether an inline function is inlined or no hzhuo1 (AT) gmail (DOT) com wrote: Quote: ===================================== MODERATOR'S COMMENT: Let's keep replies on-topic: What the Standard says or should say about function ininling. ===================================== END OF MODERATOR'S COMMENT The message that was posted was not about what the standard says or should say; he was asking how he could find out how an compiler had chosen to implement his code. I don't see how a response to that question could actually be responsive, and still be on-topic; this implies that the question itself was off-topic, and therefore should have bee rejected. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Jack Klein Guest Posted: Sun Jul 23, 2006 10:46 pm    Post subject: Re: How to judge whether an inline function is inlined or no On Sun, 23 Jul 2006 08:53:03 CST, "hzhuo1 (AT) gmail (DOT) com" <hzhuo1 (AT) gmail (DOT) com> wrote in comp.std.c++: Quote: ===================================== MODERATOR'S COMMENT: Let's keep replies on-topic: What the Standard says or should say about function ininling. ===================================== END OF MODERATOR'S COMMENT It is well known that a function can be explicitly declared inline using the keyword "inline". But the compiler doesn't make sure the inline function is really inlined. For example, in the following code, the function f is declared inline, but how can we judge whether the compiler substitudes the function call with its implementation code, or just give a function call? I will be appreciative if anyone can give some suggestions. Zhuo Hao July 23rd,2006 The code is as follows: #include<iostream using namespace std; inline void f(){ cout<<"Hello"; cout<<" World!"<<endl; } int main(){ f(); return 1; } Respecting the moderator's comment, the C++ standard says absolutely nothing about whether or not a compiler actually honors the request to expand a function's body in line. Some implementations have options to emit some sort of message when they decide not to honor an inline request. This is a QOI issue, and if your compiler does not provide such an option you might consider contacting the vendor or maintainers and requesting one. Something that one can do with any implementation is to examine the generated output to see whether or not a function is actually inlined. That, of course, is outside the scope of the language standard and is implementation specific. As to whether the standard should require a diagnostic from the translator whenever it does not, or does, inline a function when requested, I would be against it. It could generate a lot of spurious warnings. But as a QOI issue, having the ability to turn such messages on when desired, and off when not desired, is a nice feature. In general, it only really matters if a completed, correct program runs too slowly, and needs to be optimized. In that case there are tools, such as profilers, that can determine if non inlined functions are a cause of the problem. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://c-faq.com/ comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top James Dennett Guest Posted: Sun Jul 23, 2006 11:16 pm    Post subject: Re: How to judge whether an inline function is inlined or no kuyper (AT) wizard (DOT) net wrote: Quote: hzhuo1 (AT) gmail (DOT) com wrote: ===================================== MODERATOR'S COMMENT: Let's keep replies on-topic: What the Standard says or should say about function ininling. ===================================== END OF MODERATOR'S COMMENT The message that was posted was not about what the standard says or should say; he was asking how he could find out how an compiler had chosen to implement his code. I don't see how a response to that question could actually be responsive, and still be on-topic; this implies that the question itself was off-topic, and therefore should have bee rejected. I believe that a response noting that the standard does not address this, and possibly why, would be responsive and topical. Jack Klein's post seems to illustrate this fairly well. (I'm not the moderator who approved the original question, but the decision to approve seems reasonable to me.) I do, however, agree that there's not much more that can be said that is topical here. -- James --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top hzhuo1@gmail.com Guest Posted: Mon Jul 24, 2006 4:53 am    Post subject: Re: How to judge whether an inline function is inlined or no Jack Klein wrote: Quote: Respecting the moderator's comment, the C++ standard says absolutely nothing about whether or not a compiler actually honors the request to expand a function's body in line. Some implementations have options to emit some sort of message when they decide not to honor an inline request. This is a QOI issue, and if your compiler does not provide such an option you might consider contacting the vendor or maintainers and requesting one. Something that one can do with any implementation is to examine the generated output to see whether or not a function is actually inlined. That, of course, is outside the scope of the language standard and is implementation specific. As to whether the standard should require a diagnostic from the translator whenever it does not, or does, inline a function when requested, I would be against it. It could generate a lot of spurious warnings. But as a QOI issue, having the ability to turn such messages on when desired, and off when not desired, is a nice feature. In general, it only really matters if a completed, correct program runs too slowly, and needs to be optimized. In that case there are tools, such as profilers, that can determine if non inlined functions are a cause of the problem. Thanks for your advice. The standard says that it depends on the compiler whether to do the inlining or not. I tested my code with vc++8.0 and found it not inlined in debug mode but inlined in release mode. Zhuo Hao --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Gennaro Prota Guest Posted: Tue Jul 25, 2006 9:10 am    Post subject: Re: How to judge whether an inline function is inlined or no On Sun, 23 Jul 2006 17:46:11 GMT, jackklein (AT) spamcop (DOT) net (Jack Klein) wrote: Quote: Respecting the moderator's comment, the C++ standard says absolutely nothing about whether or not a compiler actually honors the request to expand a function's body in line. It's also worth noticing that though from a declarative standpoint the inline specifier applies to a function (function declaration) the "inlining" process is relative to a function call, and the compiler can (with good reasons) inline some of the calls and not others. Importantly, inlining can be decided at increasingly wider contexts as compiler technology progresses: it used to be established at the translation unit level, but many implementations are now capable of "link time code generation" (which implies they could even inline a call to a function written in another language, for instance). And there are profile directed optimizations: choose what and where to inline based on instrumented runs. Managed environments and JIT compilers go even further with "runtime inlining". All these techniques progressively move the decision were more information exist to decide. In light of this one might argue that the inline keyword is more a solution to remove some of programmers' misplaced concerns than a genuine technical tool. -- Gennaro Prota --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Francis Glassborow Guest Posted: Tue Jul 25, 2006 3:48 pm    Post subject: Re: How to judge whether an inline function is inlined or no In article <h4oac2t1rnb5mmu91fiiso4sp4no7v95vr (AT) 4ax (DOT) com>, Gennaro Prota <gennaro_prota (AT) yahoo (DOT) com> writes Quote: All these techniques progressively move the decision were more information exist to decide. In light of this one might argue that the inline keyword is more a solution to remove some of programmers' misplaced concerns than a genuine technical tool. Though originally motivated by the desire to make programmers feel more comfortable with short functions (such as member functions that provide access to the state of an object) its only 'semantic' value in C++ is in allowing multiple (though identical) definitions across TUs. -- Francis Glassborow ACCU Author of 'You Can Do It!' and "You Can Program in C++" see http://www.spellen.org/youcandoit For project ideas and contributions: http://www.spellen.org/youcandoit/projects --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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