Re: POD initialization

From:
"Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Tue, 19 Jun 2007 20:26:47 -0400
Message-ID:
<Gs-dnXuMXtTa6eXbnZ2dnUVZ_jqdnZ2d@comcast.com>
pallav wrote:

I have the following structs below.

static PinDelayPtr unspecifiedPipoDelayModel(new PinDelay());

#define DELAY_VALUE_NOT_GIVEN -7654321.0

typedef boost::shared_ptr<struct PinDelay> PinDelayPtr

struct DelayTime
{
 double rise;
 double fall;

 DelayTime();
 DelayTime(const double r, const double f);
};

struct PinDelay
{
 DelayTime block;
 DelayTime drive;
 double load;
 double maxload;
 DelayTime usertime;

 PinDelay();

 PinDelay::PinDelay(const double pload, const double pmaxload,
                    const double brise, const double frise,
                    const double bfall, const double ffall,
                    const double urise, const double ufall);
};

struct DelayWireLoadTable
{
 double slope;
 unsigned int npinset;
 std::vector<double> pins;
};


The struct above is not a POD-struct. It contains a 'vector',
which is non-POD. When an object of this struct is default-
initialised, each member is default-initialised. For the 'pins'
vector it means to default-initialise (invoke the constructor),
for built-ins it means to NOT initialise.

struct DelayCircuitImpl
{
 DelayTime defarr;
 DelayTime defreq;
 DelayWireLoadTable wltable;
 PinDelayPtr pipomodel;
};

My constructors looks like the following:

DelayTime::DelayTime()
 : rise(DELAY_VALUE_NOT_GIVEN), fall(DELAY_VALUE_NOT_GIVEN) {}

PinDelay::PinDelay()
 : load(DELAY_VALUE_NOT_GIVEN), maxload(DELAY_VALUE_NOT_GIVEN) {}

DelayCircuit::DelayCircuit()


I don't see this class anywhere.

 : dc(new DelayCircuitImpl())
{


If you look at 'dc->wltable' _right_here_, what would it be?
I would say that both 'slope' and 'npinset' would have garbage.

 dc->wltable.slope = DELAY_VALUE_NOT_GIVEN;
 dc->pipomodel = PinDelayPtr(new
PinDelay(*unspecifiedPipoDelayModel));
}

Since the struct contain POD (plain old data), I would think they
should be initialized to 0.


No.

However, I am not sure why the variable
'npinset' does not get a default value of 0.


It's not supposed to. Add a constructor to your 'DelayCircuitImpl'
_and_ to 'DelayWireLoadTable'.

In my gdb output, I have
the following:
gdb) p *(*dc).dc
$4 = {
 defarr = {
   rise = -7654321,
   fall = -7654321
 },
 defreq = {
   rise = -7654321,
   fall = -7654321
 },
 wltable = {
   slope = -7654321,
   npinset = 6311712,
   pins = {
     <std::_Vector_base<double,std::allocator<double> >> = {
       _M_impl = {
         <std::allocator<double>> = {
           <__gnu_cxx::new_allocator<double>> = {<No data fields>},
<No data fields>},
         members of std::_Vector_base<double,std::allocator<double>

:_Vector_impl:

         _M_start = 0x0,
         _M_finish = 0x0,
         _M_end_of_storage = 0x0
       }
     }, <No data fields>}
 },
 pipomodel = {
   px = 0x602960,
   pn = {
     pi_ = 0x6029b0
   }
 }
}

Everything looks good except, npinset has a garbage value. Is there
something I am not understanding about POD initialization? Something
in my code that is preventing npinset to be initialized to 0? Any
clarification is appreciation.


How about this:
------------------------------
#include <vector>
struct A {
    int a;
    std::vector<int> vi;
};

#include <iostream>
struct B {
    A *pa;
    B() : pa(new A()) {
        std::cout << pa->a << ' ' << pa->vi.size() << std::endl;
    }
};

int main() {
    B b;
}
-----------------------------
It should print something non-zero and then 0.

V
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