Re: [Boost-users] [Boost.Format] empty string argument causes VC 8.0 to assert

On 11/28/05, Mick Hollins wrote:

The following code causes a runtime assertion in VC 8.0:

std::string l_param; std::string l_str = (boost::format("here is an empty string: %1%") % l_param).str();

It passes an empty string argument to boost::format. The assert is inside the implementation of basic_string::append() and boils down to the fact that the implementation of boost::format ends up calling basic_string::append(const char *, size_type) with a null pointer, which causes basic_string::append to assert.

::_Inside(const char * _Ptr=0x00000000) Line 2023 + 0x13 bytes C++ msvcp80d.dll!std::basic_string & res="", const char * beg=0x00000000, unsigned int size=0, int w=0, const char fill_char=' ', int f=513, const char prefix_space=0, bool

This assertion seems to only happen with /MDd (e.g. debug runtime), but I'd say it qualifies as a bug in Boost.Format. Here's the stack trace: msvcp80d.dll!std::_Debug_message(const wchar_t * message=0x105157a0, const wchar_t * file=0x10514a0c, unsigned int line=2023) Line 23 C++ msvcp80d.dll!std::_Debug_pointer<char>(const char * _First=0x00000000, const wchar_t * _File=0x10514a0c, unsigned int _Line=2023) Line 1334 + 0x12 bytes C++ msvcp80d.dll!std::basic_string

const &>(const std::basic_string & x="", const boost::io::detail::format_item & res="", boost::io::basic_altstringbuf(boost::basic_format & self={...}, const std::basic_string & x="") Line 242 + 0x3f bytes C++ format.exe!boost::io::detail::feed(boost::basic_format & self={...}, const std::basic_string & x="") Line 251 + 0xd bytes C++ format.exe!boost::basic_format

...

(const std::basic_string

And here's the offending code from boost::io::detail::mk_str (feed_args.hpp): typedef typename std::basic_string::size_type size_type; res.resize(0); if(w<=0 || static_cast(w) <=size) { // no need to pad. res.reserve(size + !!prefix_space); if(prefix_space) res.append(1, prefix_space); => res.append(beg, size); } I think the simple and obvious fix is to just check for size != 0 before calling res.append, but I'm not familiar with this code. -- Caleb Epstein caleb dot epstein at gmail dot com