Question

In my program I want to use asserts that show an error message. Apart from the well known workarounds for C and C++ there’s the “real” solution as BOOST offers BOOST_ASSERT_MSG( expr, msg ) (see also assert() with message)

But a static message isn’t enough for me, I also want to show sometimes the failed variables, e.g. in a case like

BOOST_ASSERT_MSG( length >= 0, "No positive length found! It is " << length )

As you can see I’d like to format the message “string” as an stringstream or ostream as that’d allow me to easily show custom types (assuming I’ve defined the relevant formating function).

The problem here is that BOOST_ASSERT_MSG is by default requiring a char const * so that’s not compatible.

Is there a way to redefine / overload assertion_failed_msg() in such a way that using a stream as message will work? How?
(My naive approach failed as the compiler first wanted to do an operator<<("foo",bar) on the message itself…)

Answer 1

You could define your own macro

#define ASSERT_WITH_MSG(cond, msg) do \
{ if (!(cond)) { std::ostringstream str; str << msg; std::cerr << str.str(); std::abort(); } \
} while(0)