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hi all, I have a set of 40-50 global variables. I put all of them in one .h file say define.h. This define.h is included in some 6 files. CCS says that the variables are already defined (this is due 2 multiple inclusions) and gives error. I tried 2 work around the problem using the K & R approach: #ifndef _DEFINE_H #define _DEFINE_H /*contents of define.h*/ #endif But this also doesn't work what might be the possible reason? Rajesh ________________________________________________________________________ Yahoo! India Matrimony: Find your partner online. Go to http://yahoo.shaadi.com |
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problem with conditional compilation
Started by ●October 20, 2003
Reply by ●October 20, 20032003-10-20
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--- Raj <> wrote: > I have a set of 40-50 global variables. I put all > of > them in one .h file say define.h. !!! error !!! header files *.h are not meant for defining variables... they are meant for declaring variables, so the compiler knows the type of the variable and that the variable is defined somewhere else... so - my advice is - define all your global variables in a *.c file and then declare them in the *.h file... then you can include that *.h file in any *.c file you want - using compiler directives #ifndef and #define the way you described further on is obviously a good manner... > This define.h is > included in some 6 files. CCS says that the > variables > are already defined (this is due 2 multiple > inclusions) and gives error. I tried 2 work around > the > problem using the K & R approach: > #ifndef _DEFINE_H > #define _DEFINE_H > /*contents of define.h*/ > #endif > But this also doesn't work > what might be the possible reason? seems to me like "C language" problem rather than C6x problem ;-) good luck... Wojciech Rewers __________________________________ |
Reply by ●October 20, 20032003-10-20
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Rajesh- > I have a set of 40-50 global variables. I put all of > them in one .h file say define.h. This define.h is > included in some 6 files. CCS says that the variables > are already defined (this is due 2 multiple > inclusions) and gives error. I tried 2 work around the > problem using the K & R approach: > #ifndef _DEFINE_H > #define _DEFINE_H > /*contents of define.h*/ > #endif > But this also doesn't work > what might be the possible reason? I know why it does not work. But please I ask you to try to explain the problem better; for example, what is your error message? Simply saying "this does not work, please help me" is not showing everyone a good effort and makes it harder for people to help you. At least half of engineering is just communicating and asking the right questions :-) -Jeff |
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Reply by ●October 21, 20032003-10-21
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hi , I want all the global variables(say a b c d) at one place say some define.h and the in all the project files I want to include this define.h. For every such inclusion excepting the file that is linked first, I get the error message variable a b c d are already declared(if i include in 5 files I get 16 errors). To come around this problem i used K &R approach #ifndef _DEFINE_H #define _DEFINE_H /* contents of define.h*/ #endif. Even then I get the same error messages. Somebody had suggested u make it as my_define.h that also doesn't work. somebody said u declare all the variables in .c file and make extern declarations in .h file and include that .h file in all the files. This approach also didn't work So I am trying to figure out what is the problem. I guess this explains my problem better Rajesh Jeff Brower <> wrote: Rajesh- > I have a set of 40-50 global variables. I put all of > them in one .h file say define.h. This define.h is > included in some 6 files. CCS says that the variables > are already defined (this is due 2 multiple > inclusions) and gives error. I tried 2 work around the > problem using the K & R approach: > #ifndef _DEFINE_H > #define _DEFINE_H > /*contents of define.h*/ > #endif > But this also doesn't work > what might be the possible reason? I know why it does not work. But please I ask you to try to explain the problem better; for example, what is your error message? Simply saying "this does not work, please help me" is not showing everyone a good effort and makes it harder for people to help you. At least half of engineering is just communicating and asking the right questions :-) -Jeff _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: Send an email to To Post: Send an email to To Leave: Send an email to Archives: http://www.yahoogroups.com/group/c6x Other Groups: http://www.dsprelated.com ">http://docs.yahoo.com/info/terms/ i Yahoo! India Matrimony: Find your partner online.Post your profile. |
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Reply by ●October 21, 20032003-10-21
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Hi Raj, Are you using the -d option? Bhooshan >hi all, >I have a set of 40-50 global variables. I put all of >them in one .h file say define.h. This define.h is >included in some 6 files. CCS says that the variables >are already defined (this is due 2 multiple >inclusions) and gives error. I tried 2 work around the >problem using the K & R approach: >#ifndef _DEFINE_H >#define _DEFINE_H >/*contents of define.h*/ >#endif >But this also doesn't work >what might be the possible reason? >Rajesh > > >________________________________________________________________________ >Yahoo! India Matrimony: Find your partner online. >Go to http://yahoo.shaadi.com > > >_____________________________________ >Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. > >_____________________________________ >About this discussion group: > >To Join: Send an email to c...@yahoogroups.com > >To Post: Send an email to c...@yahoogroups.com > >To Leave: Send an email to c...@yahoogroups.com > >Archives: http://www.yahoogroups.com/group/c6x > >Other Groups: http://www.dsprelated.com > > > > >Calling all NRIs! Avail of the best financial services. Smile all the way with ICICI Bank. |
Reply by ●October 21, 20032003-10-21
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Raj- > I want all the global variables(say a b c d) at one place say some > define.h and the in all the project files I want to include this > define.h. For every such inclusion excepting the file > that is linked first, I get the error message variable a b c d are > already declared(if i include in 5 files I get 16 errors). To > come around this problem i used K &R approach > #ifndef _DEFINE_H > #define _DEFINE_H > /* contents of define.h*/ > #endif. > Even then I get the same error messages. Try something like this: #ifndef _GLOBALS #define DECLSPEC #else #define DECLSPEC extern #endif DECLSPEC int a; DECLSPEC int b; . . . then pick only *one* .c file and define _GLOBALS prior to including define.h, for example main.c: #define _GLOBALS #include define.h #undef _GLOBALs The idea is that *one* time the variables are declared (instantiated) and use up mem space. All other times they are referenced as extern. -Jeff |
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Reply by ●October 21, 20032003-10-21
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I second Jeff's suggestion. I have used this method for over 10 years
and it works great. Paul -----Original Message----- From: Jeff Brower [mailto:] Sent: Tuesday, October 21, 2003 1:36 AM To: Rajesh Cc: Subject: Re: [c6x] problem with conditional compilation Raj- > I want all the global variables(say a b c d) at one place say some > define.h and the in all the project files I want to include this > define.h. For every such inclusion excepting the file > that is linked first, I get the error message variable a b c d are > already declared(if i include in 5 files I get 16 errors). To > come around this problem i used K &R approach > #ifndef _DEFINE_H > #define _DEFINE_H > /* contents of define.h*/ > #endif. > Even then I get the same error messages. Try something like this: #ifndef _GLOBALS #define DECLSPEC #else #define DECLSPEC extern #endif DECLSPEC int a; DECLSPEC int b; . . . then pick only *one* .c file and define _GLOBALS prior to including define.h, for example main.c: #define _GLOBALS #include define.h #undef _GLOBALs The idea is that *one* time the variables are declared (instantiated) and use up mem space. All other times they are referenced as extern. -Jeff _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: Send an email to To Post: Send an email to To Leave: Send an email to Archives: http://www.yahoogroups.com/group/c6x Other Groups: http://www.dsprelated.com ">http://docs.yahoo.com/info/terms/ |
Reply by ●October 21, 20032003-10-21
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--- Jeff Brower <> wrote: > Try something like this: > > #ifndef _GLOBALS > > #define DECLSPEC > > #else > > #define DECLSPEC extern > > #endif > DECLSPEC int a; > DECLSPEC int b; > . > . > . > > then pick only *one* .c file and define _GLOBALS > prior to including define.h, for > example main.c: > > #define _GLOBALS > #include define.h > #undef _GLOBALs > > The idea is that *one* time the variables are > declared (instantiated) and use up mem > space. All other times they are referenced as > extern. god... Jeff... with all the respect... I think what you're proposing is nasty! if you go back to the first "C language lesson" one can learn what the difference between *.h files and *.c files is... I told the original poster what to do: 1. define all variables in *.c file and 2. declare them in *.h file then all you need to do is to include the *.h file in all your c files where you want to have the access to the variables... the header files with all those declarations are just for the compiler so it knows what the variables' types are... it's all clean and it's just C - nothing more... plus - let's keep the C naming style - you say: > The idea is that *one* time the variables are > declared (instantiated) and use up mem > space. All other times they are referenced as > extern. I would say - the variable needs to be _defined_ once in the *.c source file and it needs to be _declared_ in the *.h header file... and to the OP: try creating a simple project with a couple of variables - learn to walk before you run - as he explained in the first post that he has some 40 something variables... well - as I said - keep it simple and clean... good luck to all you ;-) Wojciech Rewers __________________________________ |
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Reply by ●October 21, 20032003-10-21
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--- Raj <> wrote: > I want all the global variables(say a b c d) at one > place say some define.h and the in all the project > files I want to include this define.h. For every > such inclusion excepting the file that is linked > first, I get the error message variable a b c d are > already declared(if i include in 5 files I get 16 > errors). well... are you really sure the compiler tells you that your variables are already _declared_? from what you're explaining - you are double (or multiple) _defining_ them! Learn what the difference between definition and declaration is! definition is the process of creating (instantiating) a variable - you are supposed to do that in *.c (and not *.h) file... declaration is just to tell the compiler the type of the specified variable - which itself (that variable) is defined somewhere in the souce (*.c) file and will be linked later on... god... those are the C language basics! it's really useful to learn them! > somebody said u declare all the variables in .c file > and make extern declarations in .h file and include > that .h file in all the files. well - that was me - but you misunderstood me (or can't even quote) - I told you to _define_ all the variables in *.c file and _declare_ them as extern in the header (*.h) file! then you include that header file in some source (*.c) files where the compiler needs to know the type of your variables defined in some other source files! > This approach also didn't work > So I am trying to figure out what is the problem. > I guess this explains my problem better well... many times I only give "hints" and I'm not really sure about whether it's gonna work, or not... well - this time is different... this time I know for sure that what I'm saying is 100% correct!!! you just have to know the difference between _definition_ and _declaration_ god - I did repeat everything at least 3 times - didn't I? well - good luck to you all ;-) Wojciech Rewers __________________________________ |
Reply by ●October 21, 20032003-10-21
Wojciech Rewers wrote:I think he already did that by looking at his original posting. He tried to put all the variables in one define.h and include this define.h in other project files.--- Jeff Brower <j...@signalogic.com> wrote:Try something like this: #ifndef _GLOBALS #define DECLSPEC #else #define DECLSPEC extern #endif DECLSPEC int a; DECLSPEC int b; . . . then pick only *one* .c file and define _GLOBALS prior to including define.h, for example main.c: #define _GLOBALS #include define.h #undef _GLOBALs The idea is that *one* time the variables are declared (instantiated) and use up mem space. All other times they are referenced as extern.god... Jeff... with all the respect... I think what you're proposing is nasty! if you go back to the first "C language lesson" one can learn what the difference between *.h files and *.c files is... I told the original poster what to do: 1. define all variables in *.c file and 2. declare them in *.h file My guess of his real problem is he somehow *re-declares* those variables in the .c files, which is not likely to happen for most engineers. Given the fact that he is still at the very begining stage of the C programming, I wouldn't think my guess is too wild. Hey Raj, why don't you post your define.h file and one project file that has the compile error. Just cut and paste the relevant section of code. That will solve the puzzle of "what the heck is going on". :-) Good luck to everybody! We do need some luck along the road, right? :-) Janethen all you need to do is to include the *.h file in all your c files where you want to have the access to the variables... the header files with all those declarations are just for the compiler so it knows what the variables' types are... it's all clean and it's just C - nothing more... plus - let's keep the C naming style - you say:The idea is that *one* time the variables are declared (instantiated) and use up mem space. All other times they are referenced as extern.I would say - the variable needs to be _defined_ once in the *.c source file and it needs to be _declared_ in the *.h header file... and to the OP: try creating a simple project with a couple of variables - learn to walk before you run - as he explained in the first post that he has some 40 something variables... well - as I said - keep it simple and clean... good luck to all you ;-) Wojciech Rewers |
