On Darwin (MacOS X) systems CPLGetSymbol() may not find the symbol.

[jhayes@…]

On Mach-o based systems C symbols have a leading underscore and depending on how
dlcompat is configured it may or may not add the leading underscore.

I'm using gdal-1.2.0 on MacOS X.3.? with fink's dlcompat.  I have not tried it
with 10.3 version of dlcompat.

Here is a patch that adds a leading underscore if dlsym fails.

======================

void *CPLGetSymbol( const char * pszLibrary, const char * pszSymbolName )

{
    void        *pLibrary;
    void        *pSymbol;

    pLibrary = dlopen(pszLibrary, RTLD_LAZY);
    if( pLibrary == NULL )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "%s", dlerror() );
        return NULL;
    }

    pSymbol = dlsym( pLibrary, pszSymbolName );
#if (defined(__APPLE__) && defined(__MACH__))
    /* On mach-o systems, C symbols have a leading underscore and depending
     * on how dlcompat is configured it may or may not add the leading
     * underscore.  So if dlsym() fails add an underscore and try again.
     */
    if( pSymbol == NULL )
    {
       char withUnder[strlen(pszSymbolName) + 2];
       withUnder[0] = '_'; withUnder[1] = 0;
       strcat(withUnder, pszSymbolName);
       pSymbol = dlsym( pLibrary, withUnder );
    }
#endif
    if( pSymbol == NULL )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "%s", dlerror() );
        return NULL;
    }

    return( pSymbol );
}

======================

[warmerdam]

Patch applied. 

Thanks!