C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  preprocessor          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Guest Posted: Sat Feb 28, 2004 1:55 am    Post subject: preprocessor I have a preprocessor constant (SUPPORT_PNG_IMAGE) with 3 states, to control the compilation: --------- #undef SUPPORT_PNG_IMAGE #define SUPPORT_PNG_IMAGE #define SUPPORT_PNG_IMAGE ONLY --------- With the 1st & 3rd line the following line works --------- #if SUPPORT_PNG_IMAGE == ONLY --------- but with the 2nd, compiler throws: --------- fatal error C1017: invalid integer constant expression --------- how can I handle this? thanks Back to top Leor Zolman Guest Posted: Sat Feb 28, 2004 2:32 am    Post subject: Re: preprocessor On Sat, 28 Feb 2004 03:55:05 +0200, "<- Chameleon ->" <cham_gss (AT) hotmail (DOT) NOSPAM.com> wrote: Quote: I have a preprocessor constant (SUPPORT_PNG_IMAGE) with 3 states, to control the compilation: --------- #undef SUPPORT_PNG_IMAGE #define SUPPORT_PNG_IMAGE #define SUPPORT_PNG_IMAGE ONLY --------- With the 1st & 3rd line the following line works --------- #if SUPPORT_PNG_IMAGE == ONLY --------- but with the 2nd, compiler throws: --------- fatal error C1017: invalid integer constant expression --------- how can I handle this? I'd suggest sticking with one of the following conventions or the other for defining SUPPORT_PNG_IMAGE: Convention #1: Either it is defined or it isn't. Convention #2: It has a non-empty value, and we'll be testing it. The first convention, testable with any of the following: #ifdef SUPPORT_PNG_IMAGE #ifndef SUPPORT_PNG_IMAGE #if defined(SUPPORT_PNG_IMAGE) #if !defined(SUPPORT_PNG_IMAGE) is good enough for either/or situations. The second, testable with #if SYMBOL == whatever is suitable for having many mutually exclusive conditional compilation blocks. You /can/ get where you want to go with the convention you've already established, if you absolutely have to: #if !defined(SUPPORT_PNG_IMAGE) // your 1st case #if defined(SUPPORT_PNG_IMAGE) && SUPPORT_PNG_IMAGE != ONLY // case 2 #if defined(SUPPORT_PNG_IMAGE) && SUPPORT_PNG_IMAGE == ONLY // case 3 but it is not very orthogonal. BTW, ONLY has been previously #defined, right? -leor Quote: thanks Leor Zolman BD Software [email]leor (AT) bdsoft (DOT) com[/email] www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix C++ users: Download BD Software's free STL Error Message Decryptor at www.bdsoft.com/tools/stlfilt.html Back to top Andrey Tarasevich Guest Posted: Sat Feb 28, 2004 2:57 am    Post subject: Re: preprocessor <- Chameleon -> wrote: Quote: I have a preprocessor constant (SUPPORT_PNG_IMAGE) with 3 states, to control the compilation: --------- #undef SUPPORT_PNG_IMAGE #define SUPPORT_PNG_IMAGE #define SUPPORT_PNG_IMAGE ONLY --------- With the 1st & 3rd line the following line works --------- #if SUPPORT_PNG_IMAGE == ONLY --------- but with the 2nd, compiler throws: --------- fatal error C1017: invalid integer constant expression --------- how can I handle this? ... I assume that 'ONLY' is not #defined anywhere. Right? In the first case (when 'SUPPORT_PNG_IMAGE' is not defined) the preprocessor replaces both 'SUPPORT_PNG_IMAGE' and 'ONLY' with '0', which means that your '#if' will turn into #if 0 == 0 In the second case (when 'SUPPORT_PNG_IMAGE' is defined as nothing), your '#if' will turn into #if == 0 In the third case after full replacement you'll again end up with #if 0 == 0 Note, that the second variant is invalid (that's what causes the error). Not also that the first and the third variant produce the same result. Maybe you should try to do something like this instead #define SPI_NONE 0 #define SPI_ONLY 1 #define SPI_ALL 2 then do #define SUPPORT_PNG_IMAGE SPI_ONLY // or SPI_NONE, or SPI_ALL and implement the '#if' as follows #if SUPPORT_PNG_IMAGE == SPI_ONLY ... or #if SUPPORT_PNG_IMAGE < SPI_ALL ... etc. -- Best regards, Andrey Tarasevich 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.