programing error

programing error

[Baloff]

Hello

coding in C++, I have a linked list to store int, but when I store
double it is not working and I tried to find out why but could not, 

thanks for looking at this problem

output************************************************************
@debian:~/Exercies/ThinkingInC++/Vol1/4thCh/7$ ./proj1
dblStash.fetch(0) = 0
dblStash.fetch(1) = 1
dblStash.fetch(2) = 2
dblStash.fetch(3) = 3
dblStash.fetch(4) = 4
freeing storage
@debian:~/Exercies/ThinkingInC++/Vol1/4thCh/7$ ./proj1
dblStash.fetch(0) = 1.6976e-313
dblStash.fetch(1) = 1.6976e-313
dblStash.fetch(2) = 1.6976e-313
dblStash.fetch(3) = 1.6976e-313
dblStash.fetch(4) = 1.6976e-313
freeing storage
@debian:~/Exercies/ThinkingInC++/Vol1/4thCh/7$

for a linked list to store int, change 'double' to 'int' in 
the lines marked (1) and (2) below


//main.cpp**************************************************
#include "stash.h"
#include <iostream>
#include <fstream>
using namespace std;

int main() {
   Stash dblStash;
   dblStash.initialize(sizeof(double)); //    (1)
   for(int i = 0; i < 5; i++)
      dblStash.add(&i);
   
   for(int j = 0; j < dblStash.count(); j++)
      cout << "dblStash.fetch(" << j << ") = "
	   << *(double*)dblStash.fetch(j) //  (2)
	   <<endl;
   dblStash.cleanup();
}

//stash.h**************************************************
struct Stash 
{
   int size;
   int quantity; //number of element in the stash
   int next;  //index of element in the stash
   unsigned char* storage; 
   
   void initialize(int size);
   int add (const void* element);
   void* fetch (int index);
   int count ();
   void inflate (int increase);
   void cleanup ();
};

//stash.cpp**************************************************
#include "stash.h"
#include <iostream>
#include <cassert>
using namespace std;

const int increment = 5;

void Stash::initialize(int sz){
   size = sz;
   quantity = 0;
   next = 0;
   storage = 0;
}

int Stash::add(const void* element){
   if(next >= quantity) //Enough space left?
      inflate(increment);
   // Copy element into storage, 
   //starting at next empty space; 
   int startBytes = next * size;
   //now lets copy byte-by-byte
   unsigned char* e = (unsigned char*)element;
   for(int i = 0; i < size; i++)
      storage[startBytes + i] = e[i];
   next++;
   return(next -1);
}

void* Stash::fetch(int index){
   assert(0 <= index);
   if(index >= next)
      return 0; //to indicate the end
   return &(storage[index * size]);
}

int Stash::count() {
   return next;
}

void Stash::inflate(int increase) {
   assert(increase > 0);
   int newQuantity = quantity + increase;
   int newBytes = newQuantity * size;
   int oldBytes = quantity * size;
   unsigned char* b = new unsigned char[newBytes];
   for(int i = 0; i<oldBytes; i++)
      b[i] = storage[i];   //copy old tonew
   delete []storage;
   storage = b;
   quantity = newQuantity;
}

void Stash::cleanup() {
   if(storage != 0) {
      cout << "freeing storage" << endl;
      delete []storage;
   }
}

Re: programing error

[Barry Margolin]

In article <8764treyeg.fsf@wash.edu>, Baloff <washdc@wash.edu> wrote:

> Hello
> 
> coding in C++, I have a linked list to store int, but when I store
> double it is not working and I tried to find out why but could not, 

What does this have to do with GNU Emacs?  Try a group like 
comp.lang.c++.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

Re: programing error

[Pascal Bourguignon]

Baloff <washdc@wash.edu> writes:

> Hello
>
> coding in C++, I have a linked list to store int, but when I store
> double it is not working and I tried to find out why but could not, 
>
> thanks for looking at this problem
>
> output************************************************************
> @debian:~/Exercies/ThinkingInC++/Vol1/4thCh/7$ ./proj1
> dblStash.fetch(0) = 0
> dblStash.fetch(1) = 1
> dblStash.fetch(2) = 2
> dblStash.fetch(3) = 3
> dblStash.fetch(4) = 4
> freeing storage
> @debian:~/Exercies/ThinkingInC++/Vol1/4thCh/7$ ./proj1
> dblStash.fetch(0) = 1.6976e-313
> dblStash.fetch(1) = 1.6976e-313
> dblStash.fetch(2) = 1.6976e-313
> dblStash.fetch(3) = 1.6976e-313
> dblStash.fetch(4) = 1.6976e-313
> freeing storage
> @debian:~/Exercies/ThinkingInC++/Vol1/4thCh/7$

You need to  put doubles into the list if you want to get doubles out of it!
This is the standard GIGO principle: garbage in, garbage out.


>       dblStash.add(&i);

Replace with:

        double d=(double)i;
        dblStash.add(&d);

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
In deep sleep hear sound,
Cat vomit hairball somewhere.
Will find in morning.

Re: programing error

[Baloff]

oops, how did this happen, sorry