C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  enums in C and C++          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Simon Elliott Guest Posted: Thu Oct 28, 2004 8:40 pm    Post subject: enums in C and C++ I'm porting thousands of lines of legacy C code to C++. One makor issue I've got is that of enums being treated differently in C and C++. There's an automatic cast from int to enum in C but not in C++. The code is full of constructs like this: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? -- Simon Elliott http://www.ctsn.co.uk Back to top Victor Bazarov Guest Posted: Thu Oct 28, 2004 8:45 pm    Post subject: Re: enums in C and C++ Simon Elliott wrote: Quote: I'm porting thousands of lines of legacy C code to C++. One makor issue I've got is that of enums being treated differently in C and C++. There's an automatic cast from int to enum in C but not in C++. The code is full of constructs like this: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? The only "clever" thing to do is to keep this C (if it worked before, why change?) V Back to top Artie Gold Guest Posted: Thu Oct 28, 2004 8:45 pm    Post subject: Re: enums in C and C++ Simon Elliott wrote: Quote: I'm porting thousands of lines of legacy C code to C++. One makor issue I've got is that of enums being treated differently in C and C++. There's an automatic cast from int to enum in C but not in C++. The code is full of constructs like this: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? Why are you bothering to port C code to C++?* Leave it in C and call what you need (from C++). HTH, --ag * - No slam on C++ intended; just a practical comment. -- Artie Gold -- Austin, Texas "If you don't think it matters, you're not paying attention." Back to top Thierry Miceli Guest Posted: Thu Oct 28, 2004 9:02 pm    Post subject: Re: enums in C and C++ Quote: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? If you really want to convert the code to C++ you could try to redefine the '|' operator for the enum. e.g: enum GardenVegetables { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 }; GardenVegetables operator|(GardenVegetables veg1, GardenVegetables veg2) { return (GardenVegetables) ((int)veg1 | (int)veg2); } Regards, Thierry www.ideat-solutions.com Back to top Julián Albo Guest Posted: Thu Oct 28, 2004 9:12 pm    Post subject: Re: enums in C and C++ "Simon Elliott" <Simon at ctsn.co.uk> wrote: Quote: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? You can write a garden_veg operator | (garden_veg, garden_veg) -- Salu2 Back to top Ioannis Vranos Guest Posted: Thu Oct 28, 2004 9:30 pm    Post subject: Re: enums in C and C++ Simon Elliott wrote: Quote: I'm porting thousands of lines of legacy C code to C++. One makor issue I've got is that of enums being treated differently in C and C++. There's an automatic cast from int to enum in C but not in C++. The code is full of constructs like this: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? Well, a quick fix could be something like: template <class T> inline T enum_cast_or(T a, T b) { return static_cast<T>(a|b); } enum SomeEnum { CARROT=0x01, TURNIP=0x02, PARSNIP=0x04, SPROUT=0x08 }; SomeEnum garden_veg = enum_cast_or(CARROT,PARSNIP); -- Ioannis Vranos http://www23.brinkster.com/noicys Back to top Jay Nabonne Guest Posted: Thu Oct 28, 2004 9:33 pm    Post subject: Re: enums in C and C++ On Thu, 28 Oct 2004 20:40:59 +0000, Simon Elliott wrote: Quote: I'm porting thousands of lines of legacy C code to C++. One makor issue I've got is that of enums being treated differently in C and C++. There's an automatic cast from int to enum in C but not in C++. The code is full of constructs like this: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? It's not really using it as an enum (once you '|' them, it's not really a value in the enumeration anymore). Do: enum garden_veg_enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 }; int garden_veg; and let it go... :) - Jay Back to top JKop Guest Posted: Fri Oct 29, 2004 8:54 am    Post subject: Re: enums in C and C++ Thierry Miceli posted: Quote: enum { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 } garden_veg; garden_veg = CARROT|PARSNIP; /* Fine in C, but not in C++ */ Do I really have to trawl through all this code and put in many hundreds of casts, or is there something clever I can do to get round this? If you really want to convert the code to C++ you could try to redefine the '|' operator for the enum. e.g: enum GardenVegetables { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 }; GardenVegetables operator|(GardenVegetables veg1, GardenVegetables veg2) { return (GardenVegetables) ((int)veg1 | (int)veg2); } return static_cast<GardenVegetables>( ( static_cast<int>(veg1) | static_cast<int>(veg2) ) ); C++, not C/C++ ;-D -JKop Back to top Siemel Naran Guest Posted: Fri Oct 29, 2004 10:36 am    Post subject: Re: enums in C and C++ "JKop" <NULL (AT) NULL (DOT) NULL> wrote Quote: Thierry Miceli posted: enum GardenVegetables { CARROT=0x01,TURNIP=0x02,PARSNIP=0x04,SPROUT=0x08 }; GardenVegetables operator|(GardenVegetables veg1, GardenVegetables veg2) { return (GardenVegetables) ((int)veg1 | (int)veg2); } return static_cast<GardenVegetables>( ( static_cast<int>(veg1) | static_cast<int>(veg2) ) ); C++, not C/C++ ;-D It seems fine to use C style casts for converting one integer/float type to another. Imagine that there exists a constructor GardenVegetables::GardenVegetables(int). Only for converting one pointer/reference type to another do I use one of the C++ style casts (usually static_cast, but sometimes reinterpret_cast). Also, instead of Quote: return (GardenVegetables) ((int)veg1 | (int)veg2); one could say return GardenVegetables ( (int(veg1) | int(veg2)) ); but neither way is superior, though I'm not sure if this second way is allowed in C. Similarly, "(size_t)i" which is equivalent to "size_t(i)" where i is an int, also seems fine to me as a good style of C++. Back to top JKop Guest Posted: Fri Oct 29, 2004 10:41 am    Post subject: Re: enums in C and C++ Quote: Similarly, "(size_t)i" which is equivalent to "size_t(i)" where i is an int, also seems fine to me as a good style of C++. See but that's why "reinterpret_cast" was given such a horrid name: float p; int* k = (int*) &p; //legal int* k = int*(&p) ; // no can do To achieve this, you need to be horrid: int* k = reinterpret_cast<int* const>(&p); I myself never use (int). Here's how I do it: Step 1) Use "static_cast". If rejected go to step 2. Step 2) Use "reinterpret_cast". I've never had to use "dynamic_cast" so far! -JKop -JKop Back to top Thierry Miceli Guest Posted: Fri Oct 29, 2004 3:32 pm    Post subject: Re: enums in C and C++ Quote: GardenVegetables operator|(GardenVegetables veg1, GardenVegetables veg2) { return (GardenVegetables) ((int)veg1 | (int)veg2); } return static_cast<GardenVegetables>( ( static_cast<int>(veg1) | static_cast<int>(veg2) ) ); C++, not C/C++ ;-D I agree, I sacrificed purity for readability. Thierry Back to top Siemel Naran Guest Posted: Sat Oct 30, 2004 10:15 am    Post subject: Re: enums in C and C++ "JKop" <NULL (AT) NULL (DOT) NULL> wrote Quote: Similarly, "(size_t)i" which is equivalent to "size_t(i)" where i is an int, also seems fine to me as a good style of C++. See but that's why "reinterpret_cast" was given such a horrid name: float p; int* k = (int*) &p; //legal int* k = int*(&p) ; // no can do I agree that for casting between pointer and reference types, it's good to use static_cast or reinterpret_cast. But for casting between value types, C style casts which behave like constructors, seem perfectly fine. Quote: To achieve this, you need to be horrid: int* k = reinterpret_cast<int* const>(&p); I myself never use (int). Here's how I do it: Step 1) Use "static_cast". If rejected go to step 2. Step 2) Use "reinterpret_cast". Agreed for pointer types only. Quote: I've never had to use "dynamic_cast" so far! It arises when writing generic code, and you can't or don't want to edit the base class by continually adding virtual functions to it. Back to top Ioannis Vranos Guest Posted: Sat Oct 30, 2004 2:06 pm    Post subject: Re: enums in C and C++ Siemel Naran wrote: Quote: I agree that for casting between pointer and reference types, it's good to use static_cast or reinterpret_cast. But for casting between value types, C style casts which behave like constructors, seem perfectly fine. C++ newer casts are still better. -- Ioannis Vranos http://www23.brinkster.com/noicys Back to top Simon Elliott Guest Posted: Mon Nov 01, 2004 10:26 am    Post subject: Re: enums in C and C++ On 28/10/2004, Simon Elliott wrote: [snip] Thanks for all the responses to this. I'm still unsure about how to proceed because there are lots of different enums which are used in lots of different ways. With the current compiler (BCB3) I have the (slightly grubby) option of suppressing the warning and leaving everything as it is. But it's possible that other compilers won't let me do this. -- Simon Elliott http://www.ctsn.co.uk 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.