format zero length string msvc-8

[drjohnfoster]

Since Microsoft have deprecated most of the standard 
library, their debug libraries also check for unsafe 
pointers. The following code gives an assertion:

(boost::format("%s") % "").str();

In debug mode, basic_string<char>::append(0, 0) 
called from mk_str in feed_args.hpp is tested by the 
macro _DEBUG_POINTER, and decides the pointer is 
invalid even though the count is 0.

I imagine this toxic behaviour is repeated in a 
number of places. It would be nice if the boost 
library could work around this problem at a low level.

[nobody]

Logged In: NO 

According to the C++ standard, basic_string<char>::append(0, 0) returns

basic_string<char>::append(basic_string<char>(0,0))

The standard specifically says the pointer shall not be a null.

So I believe that this was a bug in the boost format library, rather than a problem with the MSVC library. 

[magic_op]

Logged In: YES 
user_id=1562825
Originator: NO

This will also happen with an empty string (instead of just a character array/pointer)

std::string my_string;
(boost::format("%1%") % my_string).str();