Hello,
I'm trying to migrate from an existing solution to Boost.Log. So far
I've been able to emulate all important features of the existing library
- except one.
The existing library supported submitting a log message in multiple
statements. This is useful when the message being composed has
conditional parts, when a part of it is composed in a loop or even a
different function, something like this:
auto logmsg = log (Channel::CORE, Severity::DEBUG);
logmsg << "unconditional part";
if (condition)
logmsg << " conditional part";
for (auto element : container)
logmsg << element;
logging_subroutine (logmsg);
logmsg << endmsg;
To that end I extracted a structure from the manual_logging() function
from the Boost.Log documentation to hold the state of the message being
composed:
struct log_msg_state {
my_logger & logger;
logging::record rec;
logging::record_ostream strm;
...
...
};
Having done this, I can emulate most of the above example fairly easily
by defining a bunch of operator<<() overloads for the log_msg_state.
However, I've been struggling with record_ostream. It was a bit of a
challenge even to initialise it in the constructor - we can't use the
initialiser list as we have to make sure first that our logging::record
is valid. On the other hand, in the ctor body when the check can be
performed, it's too late as record_ostream has already been constructed
already and as it turns out, you can't do much with a constructed
instance - no usual stuff like
if (rec)
strm = logging::record_ostream (rec);
works! Fortunately, I've been able to hack around it like this:
if (rec)
new (&strm) logging::record_ostream (rec);
Not pretty but has been working well so far! However, I've failed to
find a solution for returning my log_msg_state (and thus record_ostream)
from a function. The non-copyability, non-assignability,
non-moveability are always getting in the way.
(Note also that I do NOT want to hold a pointer to record_ostream in my
log_msg_state and allocate it dynamically - that would certainly make
things easier but I don't want to penalise each and every log message
with a dynamic allocation for no good reason.)
Could someone please advise me how to get the functionality I need, a
solution or a work-around at least?
Thanks in advance
pvl
