From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael Bruck" <mbruck@rft.de>
To: <c++-embedded@cygnus.com>
Subject: Re: biggest deterrant to using C++?
Date: Sun, 23 Aug 1998 18:37:00 -0000
Message-id: <001401bdceff$cebb36c0$400581c0@avh.ins-coin.de>
X-SW-Source: 1998/msg00026.html

One of my bigger problems with using C++ in embedded projects is the
way ctors are handled. When you have global class variables the
compiler (in my case egcs) generates lots of constructor/destructor
calls for them, where they are completely uneccessary. For example:


struct general_thing {
        int    weight;

        general_thing(int _weight = 0) :  weight(_weight) {}

        virtual bool get() = 0;
};

struct atom_bomb : public general_thing {
        long    price;

        atom_bomb(long _price, int _weight = 1000) : price(_price),
general_thing(_weight) {}

        virtual bool get();
};

const    atom_bomb    my_bomb(50, 100);


I would like to have my_bomb somewhere in the ROM. And the example above
should not generate any code as long as I don't call the constructors in 
another context. What happens is, that the compiler always generates 
a function for each source file that calls all the constructors and 
then generates a section that contains the pointer to that function.
These sections from all files are then linked together into a table of
function pointers and the init-functions of all global objects are 
called at program startup through this table. This is ok if my 
constructors are doing something other than just copying around values.
This would cause in most situations just some overhead, 
but if you want to use ROM it's impossible to use (virtual) classes.



Micha