Question

I have some code which compiles fine under Linux, but I am trying to port it to Windows. I have used the Boost 1.50 precompiled binaries from Boost Pro, but when I compile my code I get this cryptic error:

error C2664: 'boost::_bi::bind_t<R,F,L>::bind_t(const boost::_bi::bind_t<R,F,L> &)' :
   cannot convert parameter 1 from 'boost::_bi::bind_t<R,F,L>'
   to 'const boost::_bi::bind_t<R,F,L> &'
   C:\Program Files (x86)\boost\boost_1_50\boost\bind\bind_cc.hpp   [line] 50

The error is most unhelpful because it shows up deep in the Boost header files, with no indication of where in my code the problem is. Nevertheless by commenting out various blocks of code I have narrowed it down to this as the cause:

void test(int a)
    throw (int)   // removing this line makes it compile
{
    return;
}
...
boost::function<void(int)> fn = boost::bind<void>(test, _1);

It works if I remove the throw specifier in the function definition. It doesn’t matter what I throw, whether it’s a class or just an int. Am I doing something wrong, or can’t you bind to functions that throw exceptions in Visual C++? The Boost Bind docs don’t seem to suggest any issues with this, and GCC doesn’t have a problem with it either way.

[Side note: The code above is not my actual code, but when compiled it exhibits the same problem. Please avoid comments about throwing ints being bad and the like, as this is only supposed to be a trivial example in case anyone wishes to reproduce the problem.]

Answer 1

I don’t know why your code fails on VC++. However, in general exception specifications are best avoided because they can introduce very subtle effects. See this excellent column A Pragmatic Look at Exception Specifications by Herb Sutter:

So here’s what seems to be the best advice we as a community have
learned as of today:

Moral #1: Never write an exception specification.

Moral #2: Except possibly an empty one, but if I were you I’d avoid
even that.