C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  throw()...Clarification          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message anand Guest Posted: Thu May 19, 2005 8:54 am    Post subject: throw()...Clarification Hi void f(); means that any type of exception may be thrown from the function. If you say void f() throw(); it means that no exceptions are thrown from a function So suppose i write a code like this #include<iostream> using namespace std; class A { public: A(int x1,int y1)(x1),y(y1){} ; int calc () throw(); private: int x,y; }; int A::calc () { int temp; temp=x-y; if(temp<0) throw 0; return temp; } int main() { A a(4,5); try{ a.calc (); }catch(...) { cout<<"Exception"< } return 0; } According to the definition of throw() calc() function should not throw any exception. But while executing the above code in am getting "Exception" as output.. Any ideas...??? I have compiled this program using vc++6.0 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maciej Sobczak Guest Posted: Thu May 19, 2005 1:45 pm    Post subject: Re: throw()...Clarification Hi, anand wrote: Quote: I have compiled this program using vc++6.0 AFAIR, this compiler ignores exception specs. You code does not compile on g++ 3.2. After adding throw() to the implementation of A::calc (it is missing in your code), the code compiles and correctly aborts when run. -- Maciej Sobczak : http://www.msobczak.com/ Programming : http://www.msobczak.com/prog/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Me Guest Posted: Thu May 19, 2005 1:51 pm    Post subject: Re: throw()...Clarification (code snipped for clarity) Quote: class A { int calc() throw(); }; int A::calc() throw() { throw 0; return 0; } According to the definition of throw() calc() function should not throw any exception. But while executing the above code in am getting "Exception" as output.. VC6 ignores throw specifications. It's partially fixed in the latest VC (http://msdn.microsoft.com/library/en-us/vclang/html/vclrf154functionexceptionspecifiers.asp) which you can get for free ([url]http://msdn.microsoft.com/visualc/vctoolkit2003/)[/url]. Here is what the compiler should translate the above code above to (by the way, your original code should not compile because you were missing a throw() signature in the function definition): int A::calc() throw() try { throw 0; return 0; } catch (...) { std::unexpected(); } where std::unexpected calls std::terminate by default, which terminates your program by default. You also seem to be confused about a few things too. Don't use throw specifications in your code (except when defining an operator new that returns NULL on failure). It is considered by some to be bad style, they can disable certain optimizations depending on your compiler ([url]http://www.boost.org/more/lib_guide.htm#Exception-specification)[/url], and most importantly, they don't mean what you think they mean (see [url]http://www.gotw.ca/publications/mill22.htm)[/url]. Don't use catch (...) in your code, there are only like 2 or 3 specific cases where it's needed. I encourage you to further read up on C++ and exception handling, exception safety is not as foolproof as some people seem to believe they are. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top        C++Talk.NET Forum Index -> C++ Language (Moderated) All times are GMT Page 1 of 1 Powered by phpBB © 2001, 2006 phpBB Group