C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Static Objects as Struct Members          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message pmatos Guest Posted: Fri Feb 25, 2005 1:03 pm    Post subject: Static Objects as Struct Members Hi all, I have a struct with a: static map<int, int> rules; Now, I want it to always be initialized with the pairs (-1, 1), (-2, 2) and (-3, 3). I don't need to dynamically add or delete pairs. I only need the struct to have this constant static map. How can I initialize it? I've tried some solutions like having in the struct constructor: rules[-1] = 1; rules[-2] = 2; rules[-3] = 3; But it doesn't work. Can somebody help me with this? Cheers, Paulo Matos Back to top Karl Heinz Buchegger Guest Posted: Fri Feb 25, 2005 1:13 pm    Post subject: Re: Static Objects as Struct Members pmatos wrote: Quote: Hi all, I have a struct with a: static map<int, int> rules; Now, I want it to always be initialized with the pairs (-1, 1), (-2, 2) and (-3, 3). I don't need to dynamically add or delete pairs. I only need the struct to have this constant static map. That's quite unusal. Why would you use a map for this, other then beeing able to use the access syntax? Why not simply struct mapping { int key; int value; } static mapping rules[] = { { -1, 1 }, {-2, 2}, {-3, 3} }; But then again, looking at the numbers, the whole rules-mapping can be replaced by simple formulas: given the value (1 .. 3), what is the correct key for it: int Rules_KeyFromValue( int Value ) { return -Value; } given a key (-1 .. -3), what is the correct value for it: int Rules_ValueFromKey( int Key ) { return -Key; } You could add some error checking (Key in range, Value in range), but basically this gives the very same functionality then your std::map. And it is simpler and faster also. Quote: How can I initialize it? I've tried some solutions like having in the struct constructor: rules[-1] = 1; rules[-2] = 2; rules[-3] = 3; Well. That wouldn't work. Mostly because rules is not some struct, but is a std::map. And the constructor for a std::map is already written and outside your reach. Just put that code somewhere into a strategic place (eg. at the very beginning of main() or some function that is called when your application starts up). But the question remains: With that requirements why do you use a std::map at all? There is really no need for it. -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Aslan Kral Guest Posted: Fri Feb 25, 2005 1:27 pm    Post subject: Re: Static Objects as Struct Members "pmatos" <pocm (AT) sat (DOT) inesc-id.pt>, haber iletisinde sunlari yazdi:1109336610.120440.22070 (AT) o13g2000cwo (DOT) googlegroups.com... Quote: Hi all, I have a struct with a: static map<int, int> rules; Now, I want it to always be initialized with the pairs (-1, 1), (-2, 2) and (-3, 3). I don't need to dynamically add or delete pairs. I only need the struct to have this constant static map. How can I initialize it? I've tried some solutions like having in the struct constructor: rules[-1] = 1; rules[-2] = 2; rules[-3] = 3; But it doesn't work. Can somebody help me with this? Cheers, Paulo Matos The following does what you want: struct staticmap : map<int, int> { staticmap() { (*this)[-1] = 1; (*this)[-2] = 2; (*this)[-3] = 3; } }; static staticmap staticrules; static map<int, int>& rules = staticrules; /*use rules as you wish*/ Back to top pmatos Guest Posted: Fri Feb 25, 2005 2:20 pm    Post subject: Re: Static Objects as Struct Members Ok, probably I didn't explain myself correctly. Of course, I don't want something like that 'literally'! I just asked the question in a way that you could understand the context and solve my problem at the same time. The issue is that I have a lot of pairs which should be put in a map to send to a library function which explicitly waits for a map. And the pairs are constant, I don't need to change them. They are not -1, 1 and -2,2 ... etc but the issue remains the same. I want to create a static map and initialize it so that I can send it to the library function that expects it. If you're just curious, the library is spirit and the map is a map of parser_id, string which associates rules identification numbers with strings which are the name of the rules, the function tree_to_xml expects this map. Since I have a list of fixed parser rules and a list of names for them I can create a map that will never be changed dynamically. Anyway, thanks for the help. Cheers, Paulo Matos Back to top pmatos Guest Posted: Fri Feb 25, 2005 2:30 pm    Post subject: Re: Static Objects as Struct Members That way won't work because rules will not be a static member of my struct. Even if inside my struct I add your code, I'll have defined staticrules which will be useless since it was defined only to define rules. Back to top Aslan Kral Guest Posted: Fri Feb 25, 2005 2:37 pm    Post subject: Re: Static Objects as Struct Members "pmatos" <pocm (AT) sat (DOT) inesc-id.pt>, haber iletisinde sunlari yazdi:1109341852.271473.11380 (AT) g14g2000cwa (DOT) googlegroups.com... Quote: That way won't work because rules will not be a static member of my struct. Even if inside my struct I add your code, I'll have defined staticrules which will be useless since it was defined only to define rules. There is no static member in the code. That answers your question regarding initializing the map before main() is entered. Of course you can do it some other ways too. Back to top Karl Heinz Buchegger Guest Posted: Fri Feb 25, 2005 3:15 pm    Post subject: Re: Static Objects as Struct Members pmatos wrote: Quote: That way won't work because rules will not be a static member of my struct. Even if inside my struct I add your code, I'll have defined staticrules which will be useless since it was defined only to define rules. I really don't understand that argumentation. What Aslan suggested was to encapsulate that map into another structure, just to get a hands on defining a constructor. That should work pretty well. In fact you never ever touch the staticrules object again. After the constructor is run, it has done its job and can be forgotten completely. But if you are unhappy with that, you can always use another dummy variable and use a function to initialize that variable. Inside that function you fill your map. static map<int, int> rules; static bool rules_init_dummy = InitRules(); static bool InitRules() { rules[-1] = 1; rules[-2] = 2; rules[-3] = 3; return true; } Again: The variable rules_init_dummy is not important. It is only there to have a way to call a function (namely 'InitRules') at program startup time. -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Aslan Kral Guest Posted: Fri Feb 25, 2005 3:38 pm    Post subject: Re: Static Objects as Struct Members "Karl Heinz Buchegger" <kbuchegg (AT) gascad (DOT) at>, haber iletisinde sunlari yazdi:421F4100.F5FCDC29 (AT) gascad (DOT) at... Quote: pmatos wrote: That way won't work because rules will not be a static member of my struct. Even if inside my struct I add your code, I'll have defined staticrules which will be useless since it was defined only to define rules. I really don't understand that argumentation. What Aslan suggested was to encapsulate that map into another structure, just to get a hands on defining a constructor. That should work pretty well. In fact you never ever touch the staticrules object again. After the constructor is run, it has done its job and can be forgotten completely. In fact staticrules can be avoided like this: #include <map> using namespace std; struct staticmap : map<int, int> { staticmap() { (*this)[-1] = 1; (*this)[-2] = 2; (*this)[-3] = 3; } }; static map<int, int>& rules = staticmap(); int main() { size_t size = rules.size(); } Back to top Jay Nabonne Guest Posted: Sat Feb 26, 2005 6:50 am    Post subject: Re: Static Objects as Struct Members On Fri, 25 Feb 2005 05:03:30 -0800, pmatos wrote: Quote: Hi all, I have a struct with a: static map<int, int> rules; Now, I want it to always be initialized with the pairs (-1, 1), (-2, 2) and (-3, 3). I don't need to dynamically add or delete pairs. I only need the struct to have this constant static map. How can I initialize it? How about: // Example class class MyClass { static std::map<int, int> rules; }; // Create an array of values. static std::pair<int, int> ruleValues[] = { std::pair<int, int>(-1, 1), std::pair<int, int>(-2, 2), std::pair<int, int>(-3, 3) }; // Pass the start and end+1 of the array std::map<int, int> MyClass::rules(ruleValues, ruleValues+sizeof(ruleValues)/sizeof(ruleValues[0])); - Jay 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.