C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  #define and commas          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Bolin Guest Posted: Fri Oct 29, 2004 8:49 pm    Post subject: #define and commas I am using a macro to define template functions that look the same except for a type. However when the return type it a template class with several template arguments (say, A<T1, T2>) then the macro does not work because of the comma -- the macro thinks there are more arguments provided since the comma separates arguments. To avoid the comma being taken into account the usual way is to put parenthesis, but here it would not work because the argument is a return type, and I cannot declare a function like (A<T1, T2>) foo(); Is there a way to get around this problem? Thanks B. Back to top Victor Bazarov Guest Posted: Fri Oct 29, 2004 9:07 pm    Post subject: Re: #define and commas Bolin wrote: Quote: I am using a macro to define template functions that look the same except for a type. However when the return type it a template class with several template arguments (say, A<T1, T2>) then the macro does not work because of the comma -- the macro thinks there are more arguments provided since the comma separates arguments. To avoid the comma being taken into account the usual way is to put parenthesis, but here it would not work because the argument is a return type, and I cannot declare a function like (A<T1, T2>) foo(); Is there a way to get around this problem? So, you have something like #define MYFUNC(T) A<T> foo##T(T t) { A<T> tt(t); return tt } and want to use it to define a function with more than one template argument? I guess I don't understand. Post more code. Alternative: define a different macro for more than one argument: #define MYFUNC1(T) ... #define MYFUNC2(T,U) ... and so on. V Back to top chris Guest Posted: Fri Oct 29, 2004 10:17 pm    Post subject: Re: #define and commas Bolin wrote: Quote: I am using a macro to define template functions that look the same except for a type. However when the return type it a template class with several template arguments (say, A<T1, T2>) then the macro does not work because of the comma -- the macro thinks there are more arguments provided since the comma separates arguments. To avoid the comma being taken into account the usual way is to put parenthesis, but here it would not work because the argument is a return type, and I cannot declare a function like (A<T1, T2>) foo(); Is there a way to get around this problem? The only way of fixing this is to declare multiple macros, one for each number of commands in the input. The is fixed in C99 with variable length macros, for example by: #define DEBUGLIST(...) fprintf(stderr, __VA_ARGS__) While this isn't in C++ yet, some compilers (in particular g++) will let you use this C99 construct in C++ code, and I would be highly suprised if it doesn't end up appearing in the very next version of C++. Chris Back to top John Harrison Guest Posted: Sat Oct 30, 2004 6:26 am    Post subject: Re: #define and commas "Bolin" <gao_bolin (AT) voila (DOT) fr> wrote Quote: I am using a macro to define template functions that look the same except for a type. However when the return type it a template class with several template arguments (say, A<T1, T2>) then the macro does not work because of the comma -- the macro thinks there are more arguments provided since the comma separates arguments. To avoid the comma being taken into account the usual way is to put parenthesis, but here it would not work because the argument is a return type, and I cannot declare a function like (A<T1, T2>) foo(); Is there a way to get around this problem? Thanks B. None that springs to mind. But the usual way to define functions (templates or not) that look the same except for a type is to use a template. So perhaps if you post the macro someone could suggest a way to make a template from it. john 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 (comp.lang.c++) 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.