C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Temporaries versus sequence points          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message Trevor L. Jackson, III Guest Posted: Fri Feb 18, 2005 10:56 pm    Post subject: Temporaries versus sequence points Given an object whose initialization requires a special machine state, and which machine state has to be restored once the object's constructor has completed, I am tempted to use a temporary in the constructor initialization list. For example: struct Tmp { // Manage machine state state_t state_; Tmp() : state_( true ) {} ~Tmp() { state_ = false; } } struct Object { // Depends in special machine state data_t data_; Object : data_( Tmp(), /* init_expr goes here*/ ) {} } However, if the temporary Tmp is not certain to survive past the comma then I have to eliminate the sequence point at some cost in clarity. Does the temporary Tmp in the initialization list of the Object constructor last until the end of the full expression (the closing parenthesis) or only until the next sequence point (the comma operator)? /tj3 --- [ 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.jamesd.demon.co.uk/csc/faq.html ] Back to top Matti Rintala Guest Posted: Sat Feb 19, 2005 7:24 pm    Post subject: Re: Temporaries versus sequence points Trevor L. Jackson, III wrote: Quote: struct Tmp { // Manage machine state state_t state_; Tmp() : state_( true ) {} ~Tmp() { state_ = false; } } struct Object { // Depends in special machine state data_t data_; Object : data_( Tmp(), /* init_expr goes here*/ ) {} } Does the temporary Tmp in the initialization list of the Object constructor last until the end of the full expression (the closing parenthesis) or only until the next sequence point (the comma operator)? Yes, it survives: 12.2 3: "Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created." Here a full expression is the whole comma expression, so the temporary object is destroyed at the end of it. -- ------------- Matti Rintala ------------ [email]matti.rintala (AT) tut (DOT) fi[/email] ------------ Painting is the art of inclusion. Photography is an art of exclusion. --- [ 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.jamesd.demon.co.uk/csc/faq.html ] Back to top Trevor L. Jackson, III Guest Posted: Sun Feb 20, 2005 12:05 am    Post subject: Re: Temporaries versus sequence points Matti Rintala wrote: Quote: Trevor L. Jackson, III wrote: struct Tmp { // Manage machine state state_t state_; Tmp() : state_( true ) {} ~Tmp() { state_ = false; } } struct Object { // Depends in special machine state data_t data_; Object : data_( Tmp(), /* init_expr goes here*/ ) {} } Does the temporary Tmp in the initialization list of the Object constructor last until the end of the full expression (the closing parenthesis) or only until the next sequence point (the comma operator)? Yes, it survives: 12.2 3: "Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created." Here a full expression is the whole comma expression, so the temporary object is destroyed at the end of it. Thanks for the info. /tj3 --- [ 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.jamesd.demon.co.uk/csc/faq.html ] 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, library and standards 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.