[Digikam-users] potential incompatibility between exiv2-svn and exiv2-0.12

[Pedro Venda]

Hi everyone,

I am facing another compilation error, for which I do not have enough C++ 
experience to handle. I am compiling digikam along with trunk/exiv2 
and trunk/extragear/libs, I have updated the svn copy of digikam several 
times and even rm -rf and rechecked the whole trees again to rule out any 
mess I might have made.

The following error happens when compiling several objects from 
digikam/libs/widgets/metadata/:

if /bin/sh ../../../../libtool --silent --tag=CXX --mode=compile 
g++ -DHAVE_CONFIG_H -I. -I. -I../../../.. -I../../../../digikam/libs/dmetadata -I../../../../digikam/libs/dimg -I/usr/local/digikam-trunk/include   -I../../../../digikam/digikam -I/usr/kde/3.5/include -I/usr/qt/3/include -I.   -DQT_THREAD_SUPPORT  -D_REENTRANT  -Wno-long-long -Wundef -ansi -D_XOPEN_SOURCE=500 -D_BSD_SOURCE -Wcast-align -Wchar-subscripts -Wall -W -Wpointer-arith -O2 -I/usr/local/digikam-trunk/include -Wformat-security -Wmissing-format-attribute -Wno-non-virtual-dtor -fno-exceptions -fno-check-new -fno-common -DQT_CLEAN_NAMESPACE -DQT_NO_ASCII_CAST -DQT_NO_STL -DQT_NO_COMPAT -DQT_NO_TRANSLATION -DQT_CLEAN_NAMESPACE -DQT_CLEAN_NAMESPACE -DQT_NO_ASCII_CAST -DQT_NO_STL -DQT_NO_COMPAT -DQT_NO_TRANSLATION -fexceptions -MT 
iptcwidget.lo -MD -MP -MF ".deps/iptcwidget.Tpo" -c -o iptcwidget.lo 
iptcwidget.cpp; \
    then mv -f ".deps/iptcwidget.Tpo" ".deps/iptcwidget.Plo"; else 
rm -f ".deps/iptcwidget.Tpo"; exit 1; fi
iptcwidget.cpp: In member function 'virtual bool 
Digikam::IptcWidget::decodeMetadata()':                                                                      
iptcwidget.cpp:159: error: request for member 'c_str' 
in '((Exiv2::Error*)e)->Exiv2::Error::what()', which is of non-class 
type 'const char*'                 
iptcwidget.cpp: In member 
function 'virtual QString Digikam::IptcWidget::getTagTitle(const QString&)':
iptcwidget.cpp:188: error: request for member 'c_str' 
in '((Exiv2::Error*)e)->Exiv2::Error::what()', which is of non-class 
type 'const char*'                 
iptcwidget.cpp: In member 
function 'virtual QString Digikam::IptcWidget::getTagDescription(const 
QString&)':                                                  
iptcwidget.cpp:205: error: request for member 'c_str' 
in '((Exiv2::Error*)e)->Exiv2::Error::what()', which is of non-class 
type 'const char*'                 
make[5]: *** [iptcwidget.lo] Error 1                                                  

I looked at the exiv2 error.hpp (exiv2-svn) header and I found that the method
Exiv2::Error.what() already returns a (const char *) so c_str() is (probably) 
not adequate. The affected source files were: iptcwidget.cpp, exifwidget.cpp, 
gpswidget.cpp and makernotewidget.cpp.

This what() method differs in the way it is being prototyped/implemented 
between exiv2-svn and exiv2-0.12 (error.hpp). 
exiv2-svn is:
        virtual const char* what() const throw() { return msg_.c_str(); }
exiv2-0.12 is:
        virtual std::string what() const;

The call to c_str() might work if called from a std::string object, but not 
from a const char * type variable (which is not even semantically correct).
If I remove the call to c_str() on the affected objects, digikam compiles 
correctly but doesn't work. It starts and immediately after showing up the 
main screen, it segfaults with:

terminate called after throwing an instance of 'std::bad_alloc'
  what():  St9bad_alloc

Obviously, this is related to my changes on the source files. 
The next step I took was to compile digikam-svn against my system's exiv-0.12.  
It worked well, so I think I have found an incompatibility here...

I need help here from C++ developers. I suppose this should be quite simple to 
fix.

Best regards,
-- 

Pedro João Lopes Venda
email: pjvenda at pjvenda org
http://www.pjvenda.org