Joel de Guzman wrote:
Martin Apel wrote:
Hi all,
I posted this issue a week ago to the Spirit mailing list only, but I got no reply. So I repost this onto the Boost mailing list as well:
I tried to compile a Spirit grammar parsing a real number using closures under Microsoft Visual C++ 2005. The same grammar compiles fine on Linux using GCC 4.x. Boost version is 1.35.0 in both cases. As far as I understood, the error is caused by an assertion inside the closure class template: closure_frame_t& context() { assert(frame!=0); return frame.get(); } (line 352 of boost/spirit/phoenix/closures.hpp)
Even if I define NDEBUG, Phoenix closures don't compile, because the return statement after the assertion returns a pointer to a closure_frame_t and not a reference. From my point of view, this is not really a compiler issue, but a bug in the header file boost/spirit/phoenix/closures.hpp. I do not understand, why GCC compiles this without any errors, because I think the code should not compile at all. Any help would be appreciated.
Please post a minimal cpp file that exhibits the problem. Please try to make it as minimal as possible so as to focus on the problem. At any rate, have you read the FAQ:
http://spirit.sourceforge.net/distrib/spirit_1_8_5/libs/spirit/doc/faq.html#...
Regards,
Hi all, the mentioned FAQ entry is about an assertion triggered at runtime, but I don't even come that far, because the problem happens at compile time. While trying to generate a small example, I found out, what is causing the problem: I marked the grammar class using the closure with __declspec(dllexport), which causes MSVC to instantiate all members of a template, even if they are never needed. It seems that otherwise the "context" member function is never instantiated. If you remove the __declspec(dllexport), everything compiles. I still think, that the code is wrong, because it returns a pointer, where it should return a reference. I have attached a small example, which triggers the problem. By the way, the example implements a real parser, which uses the standard C++ runtime to convert the real number into a double. I had to implement this, because I found out, that the Spirit real_p parser creates numerically different results from the standard runtime, i.e. parsing the string "1.8" delivers a number like 1.8000000532 using Spirit, while the C++ runtime delivers something like 1.7999999973, which is always closer to the real value. Please note, that these numbers are not accurate, they are simply meant to demonstrate, what I mean. Regards, Martin