Re: Code that worked in gcc-2.95.2 but not in 2.96...

[llewelly at edevnull dot com]

Benjamin Scherrey <scherrey@switchco.com> writes:

> I'm trying to get my code ready for gcc 3 and the new stdc++lib 3 but
> lots of stuff simple won't compiler/link properly. Many issues are just
> a more strict compiler (which is good) but a few things I just can't
> figure. The attached code fails to link although everything its looking
> for seems quite explicitly defined. Can some one rent me a clue as to
> what my problem is? This is being built with egcs-20000911 configured
> with '--enable-shared --enable-libstdcxx-v3' in a linux 2.2.13 kernel
> for i686.
> 
>     thanx & later,
> 
>         Ben Scherrey
> //
> //  default.cpp     -   Testing default parms (or null string values).
> //
> 
> #include <iostream>
> #include <iomanip>
> #include <stdexcept>
> #include <string>
> #include <strstream>
> 
> class Default : public exception
> {
> static const char* defaulttext;
> 
> public:
> 
>     Default( void ) throw() { msg = defaulttext; }
>     
>     Default( const string& what, const string file = "", const unsigned int line = 0 ) throw()
>     {
>         strstream AMsg;
>         AMsg << defaulttext << what;
>         if( file.size() )
>         {
>             AMsg << setfill(' ') << "\t" << file;
>             
>             if( line )
>             {
>                 AMsg << " : " << setw( 4 ) << line;
>             }
>         }
>    
>         AMsg << ends;
>         msg = AMsg.str();
>     }
>     
>     virtual const char* what( void ) const throw() { return msg.c_str(); }
>     
>     friend ostream& operator<<( ostream& o, const Default& d );
>     
> private:
> 
>     string msg;
>     
> };
> 
> const char* defaulttext = "Default exception!";

You are missing a qualifier here. Try:

  const char* Default::defaulttext = "Default exception!";

> 
> ostream& operator <<( ostream& o, const Default& d ) { o << d.what(); return o; }
> 
> 
> int main( int argc, char* argv[] )
> {
>     cout << "Constructing an initial Default exception." << endl;
>     Default X( "X Exception @", __FILE__, __LINE__ );
>     cout << "X( 'X Exception @', __FILE__, __LINE__ ) = " << X << endl;
>     Default Y( "Y Exception" );
>     cout << "Y( 'Y Exception' ) = " << Y << endl;
>     
>     return 0;
> }
> 
> //
> // eof(default.cpp)
> //
> /tmp/ccMlXncj.o: In function `Default::Default(basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> > const &, basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> >, unsigned int)':
> /tmp/ccMlXncj.o(.Default::gnu.linkonce.t.(basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> > const &, basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> >, unsigned int)+0x51): undefined reference to `Default::defaulttext'
> collect2: ld returned 1 exit status

Are you sure your compiler was configured with --enable-libstdcxx-v3 ?

  (0) libstdcxx-v3 uses char_traits<>, not string_char_traits<>.

  (1) --enable-libstdcxx-v3 turns on -fhonor-std by default, so that
        things like 'cout', 'endl', 'string', etc, need appropriate
        qualifiers or using declarations.