C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How to get sizeof(MY_TYPE) after the compilation ?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Eugene Koudriavitski Guest Posted: Fri Jul 30, 2004 9:48 am    Post subject: How to get sizeof(MY_TYPE) after the compilation ? Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. As a temporary solution I created a small separate application VerifySizeOfMyType that contains only MY_TYPE declaration and std::cout< However, every time I alter MY_TYPE, I have to rebuild this small application and compare the new size with the old one. I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. I think no preprocessor instructions can help, because sizeof is a compiler operator which is calculated after preprocessing. Can you advise how to solve the problem ? Thanks, Eugene [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Daniel Frey Guest Posted: Fri Jul 30, 2004 2:59 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? Eugene Koudriavitski wrote: Quote: I want to know sizeof(MY_TYPE) after the compilation stage. Can you advise how to solve the problem ? class A { int i; double d; char c; }; void check_size() { char sizeof_A_is_[ sizeof( A ) ]; } int main() { } This prints a nice warning at the compilation stage for my compiler: t.cc:8: warning: unused variable `char sizeof_A_is_[16]' HTH, Daniel -- Daniel Frey aixigo AG - financial solutions & technology Schlo=DF-Rahe-Stra=DFe 15, 52072 Aachen, Germany fon: +49 (0)241 936737-42, fax: +49 (0)241 936737-99 eMail: [email]daniel.frey (AT) aixigo (DOT) de[/email], web: http://www.aixigo.de The hacks that we write today become the bugs of tomorrow. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maxim Yegorushkin Guest Posted: Fri Jul 30, 2004 3:22 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? Eugene Koudriavitski <evgenik1 (AT) yahoo (DOT) ca> wrote: Quote: I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. As a temporary solution I created a small separate application VerifySizeOfMyType that contains only MY_TYPE declaration and std::cout< However, every time I alter MY_TYPE, I have to rebuild this small application and compare the new size with the old one. I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. I think no preprocessor instructions can help, because sizeof is a compiler operator which is calculated after preprocessing. Can you advise how to solve the problem ? You can use static assertion like this one: #define CONCAT(x, y) CONCAT1 (x, y) #define CONCAT1(x, y) x##y #define STATIC_ASSERT(expr) typedef char CONCAT(static_assert_failed_at_line_, __LINE__) [(expr) ? 1 : -1] and then in your code STATIC_ASSERT(sizeof(MY_TYPE) == N); that will break the compilation if the expression is false. You can find an advanced version of STATIC_ASSERT in boost/static_assert.hpp -- Maxim Yegorushkin [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Francis Glassborow Guest Posted: Fri Jul 30, 2004 3:33 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? In article <007b01c475f2$ca100740$439d9c18 (AT) ym (DOT) phub.net.cable.rogers.com>, Eugene Koudriavitski <evgenik1 (AT) yahoo (DOT) ca> writes Quote: Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. As a temporary solution I created a small separate application VerifySizeOfMyType that contains only MY_TYPE declaration and std::cout< However, every time I alter MY_TYPE, I have to rebuild this small application and compare the new size with the old one. I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. I think no preprocessor instructions can help, because sizeof is a compiler operator which is calculated after preprocessing. Can you advise how to solve the problem ? I suspect that any change you make to a type that results in a change to its size (and many that do not) will force a rebuild of all code that sees the definition of the type. Those parts that do not, cannot be concerned with its size (and if you are playing games with malloc and an external knowledge of the size of the type then your code is inherently fragile and, IMO, lacks production quality). -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit For project ideas and contributions: http://www.spellen.org/youcandoit/projects [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alberto Barbati Guest Posted: Fri Jul 30, 2004 3:37 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? Eugene Koudriavitski wrote: Quote: I want to know sizeof(MY_TYPE) after the compilation stage. [...] Can you advise how to solve the problem ? Looks like you might use static assertions. Have a look here for an implementation: http://www.boost.org/libs/static_assert/static_assert.htm Regards, Alberto [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Michael Karcher Guest Posted: Fri Jul 30, 2004 4:53 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? Eugene Koudriavitski <evgenik1 (AT) yahoo (DOT) ca> wrote: Quote: I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. You are right. A sizeof expression ist a "integral constant expression", which are usable for compile-time-arithmetic. You can do something like the following example, which is a special case of compile time assertion. This make the compiler emit an error if the size is wrong. The error message should contain "checksize<TYPE,SIZE>" to tell you exactly which test fails. You can look for "static assertions" in boost to find a more elaborate version of this concept. Michael Karcher // Helper class template <typename T, int S> checksize { // Allowed array sizes in C++ start at 1. // test1 is a error if sizeof(T) < S char test1[sizeof(T) - S + 1]; // test2 is a error if sizeof(T) > S char test2[S - sizeof(T) + 1]; }; // Your critical class struct mytype { int a,b,c,d; }; // The checking code -> generates a 2 byte object (probably small enough // to not be noticable in release code, perhaps do a #ifndef NDEBUG around // it static checksize<mytype,15> checker15; // should fail static checksize<mytype,16> checker; // should compile (for 4 byte ints) static checksize<mytype,17> checker17; // should fail GCC output: g++ newsgroup.cc -o newsgroup newsgroup.cc: In instantiation of `checksize<mytype, 15>': newsgroup.cc:20: instantiated from here newsgroup.cc:8: error: creating array with size zero (`0') newsgroup.cc: In instantiation of `checksize<mytype, 17>': newsgroup.cc:22: instantiated from here newsgroup.cc:6: error: creating array with size zero (`0') Michael Karcher [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Tom Tanner Guest Posted: Sat Jul 31, 2004 3:06 am    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? "Eugene Koudriavitski" <evgenik1 (AT) yahoo (DOT) ca> wrote Quote: Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? Well, no there isn't unless you compile something and examine the source code Quote: My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. That's slightly different. There are a few macros around that allow you to check a value known at compile time. Here's one for C #define CHECK(expr) { char unnamed[(expr) ? 1 : 0]; } If you then include CHECK(sizeof(MY_TYPE) == 16); in your program, it just won't compile if the structure has been changed. If you want the check in the header, you'll have to use templates, and define an enum or a class. The basic idea is template<bool> struct Compile_Time_Check; template<> struct Compile_Time_Check<true> {}; #define CHECK(name, expr) enum { name = sizeof(Compile_Time_Check<(expr)>) } You can then add CHECK(sizecheck, sizeof(MY_TYPE) == 16); in the header after the declaration of MY_TYPE. As soon as you compile anything, if the size of MY_TYPE isn't 16 (or whatever), the compile will fail. There's probably a macro that does this even more nicely in Boost [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top tom_usenet Guest Posted: Sat Jul 31, 2004 3:08 am    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? On 30 Jul 2004 05:48:46 -0400, "Eugene Koudriavitski" <evgenik1 (AT) yahoo (DOT) ca> wrote: Quote: Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. As a temporary solution I created a small separate application VerifySizeOfMyType that contains only MY_TYPE declaration and std::cout< However, every time I alter MY_TYPE, I have to rebuild this small application and compare the new size with the old one. I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. I think no preprocessor instructions can help, because sizeof is a compiler operator which is calculated after preprocessing. Can you advise how to solve the problem ? You can make size changes cause a compiler error. e.g. typedef int checkMY_TYPE_size[sizeof(MY_TYPE) == 24]; //or however big it is That works since it is illegal to declare an array of 0 size. Better is to use a library facility: http://www.boost.org/libs/static_assert/static_assert.htm (it's easy to write your own). Tom [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dag Viken Guest Posted: Sat Jul 31, 2004 3:10 am    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? "Eugene Koudriavitski" <evgenik1 (AT) yahoo (DOT) ca> wrote Quote: Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. As a temporary solution I created a small separate application VerifySizeOfMyType that contains only MY_TYPE declaration and std::cout< However, every time I alter MY_TYPE, I have to rebuild this small application and compare the new size with the old one. I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. I think no preprocessor instructions can help, because sizeof is a compiler operator which is calculated after preprocessing. Can you advise how to solve the problem ? Thanks, Eugene If you are using Visual C with MFC and have runtime type information enabled: HMODULE hmod = GetModuleHandle("myapp.exe"); FARPROC procadd = GetProcAddress(hmod, "my mangled name"); CRuntimeClass* pClassInfo = reinterpret_cast if (pClassInfo->m_nObjectSize != sizeof(MY_TYPE)) { die(); } You can find the mangled name for GetProcAddress using depends or dumpbin. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Florian Weimer Guest Posted: Sat Jul 31, 2004 3:46 am    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? * Eugene Koudriavitski: Quote: I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? When cross-compiling, autoconf uses a binary search algorithm and the fact that an array of zero elements is ill-formed. It's rather inefficient, but it doesn't require running any compiled code. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alan Griffiths Guest Posted: Sat Jul 31, 2004 1:50 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? "Eugene Koudriavitski" <evgenik1 (AT) yahoo (DOT) ca> wrote Quote: Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? Yes. But this is probably not a solution to your underlying problem. Quote: My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. There are many other changes (re-orderings, changes of member names, types or access) that also required a recompile of any translation units that include the definition of MY_TYPE. A better solution to detecting such changes is to use your version control system to prevent edits to MY_TYPE. Quote: Can you advise how to solve the problem ? Guessing at what your real problem is, I suspect that this may point the way: http://www.octopull.demon.co.uk/c++/implementation_hiding.html -- Alan Griffiths http://www.octopull.demon.co.uk/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maxim Yegorushkin Guest Posted: Sat Jul 31, 2004 6:49 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? tom_usenet wrote: [] Quote: You can make size changes cause a compiler error. e.g. typedef int checkMY_TYPE_size[sizeof(MY_TYPE) == 24]; //or however big it is That works since it is illegal to declare an array of 0 size. The reality is that Intel C++ 8 for Windows actually allows zero sized arrays issuing only a warning. The warning may be cast to an error but it's not on by default. So, more reliable way is to use negative sizes instead of zero. That is: typedef int checkMY_TYPE_size[sizeof(MY_TYPE) == 24 ? 1 : -1]; -- Maxim Yegorushkin [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top John Torjo Guest Posted: Mon Aug 02, 2004 2:27 pm    Post subject: Re: How to get sizeof(MY_TYPE) after the compilation ? "Eugene Koudriavitski" <evgenik1 (AT) yahoo (DOT) ca> wrote Quote: Hi All, I want to know sizeof(MY_TYPE) after the compilation stage. Is there any way to get this information without building and running the project? My code is a small part of some huge project, which takes an hour to rebuild, and I want to be sure that I haven't changed the size of MY_TYPE structure, by adding and deleting its data members. As a temporary solution I created a small separate application VerifySizeOfMyType that contains only MY_TYPE declaration and std::cout< However, every time I alter MY_TYPE, I have to rebuild this small application and compare the new size with the old one. I have feeling that since the compiler knows sizeof(MY_TYPE), then it is probably possible to get it just after the compilation step without building and running any additional code. I think no preprocessor instructions can help, because sizeof is a compiler operator which is calculated after preprocessing. Can you advise how to solve the problem ? I'm not sure you're solving the right problem As Francis pointed out, such advanced uses of sizeof() are really dangerous - they require knowledge of the compiler internals, etc. - and could easily lead to broken code (especially if your module interacts with other modules). So I think the real question is: why are you concerned with the size of MY_TYPE (and its change)? Could you not redesign your code so that this won't matter? Best, John John Torjo Freelancer -- [email]john (AT) torjo (DOT) com[/email] Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ Professional Logging Solution for FREE -- http://www.torjo.com/code/logging.zip (logging - C++) -- http://www.torjo.com/logview/ (viewing/filtering - Win32) -- http://www.torjo.com/logbreak/ (debugging - Win32) (source code available) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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