C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Passing a class object by value and standard behavior.          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Alex Fennell Guest Posted: Sat Jul 16, 2005 11:38 pm    Post subject: Passing a class object by value and standard behavior. Hi all, I am doing some experiments with unit testing and as part of that I am passing a class object by value into a function. When the function returns the class object's destructor is called as I would expect. What I didn't expect is that there is no call to the copy constructor or assignment operator. I hunted in Stroustrup a bit to no avail and C++FAQs touches on the subject but does not spell it out clearly. Can anyone enlighten me as to what the standard says the behavior should be or point me in the direction of a free copy of the standard for me to look? Thanks in advance! [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Greg Guest Posted: Sun Jul 17, 2005 8:26 pm    Post subject: Re: Passing a class object by value and standard behavior. Alex Fennell wrote: Quote: Hi all, I am doing some experiments with unit testing and as part of that I am passing a class object by value into a function. When the function returns the class object's destructor is called as I would expect. What I didn't expect is that there is no call to the copy constructor or assignment operator. I hunted in Stroustrup a bit to no avail and C++FAQs touches on the subject but does not spell it out clearly. Can anyone enlighten me as to what the standard says the behavior should be or point me in the direction of a free copy of the standard for me to look? Thanks in advance! The compiler does not always need to copy a class object when a copy of that object is required. In this case, a copy of the object is required in order it to be passed by value in a function call. But if the object being copied (or less likely, the copied object) is never used again (and only its destructor will be called), then the compiler can treat the object as its own copy and simply use the original object as the parameter in the function call. Doing so of course elminates the temporary and the otherwise expected copy constructor call. Greg [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ Language (Moderated) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.