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problem with <bitset> and reinterpret_cast

AeonFlux1212 (125)
Hi! Here's some code...

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#include <cstdlib>
#include <iostream>
#include <bitset>
#include <fstream>

#define RANDOM_A      (1103515245)
#define RANDOM_C      (12345)
#define RANDOM_SHIFT  (16)

#define MAX_UNSIGNED_SHORT  (0xffff)
#define MAX_UNSIGNED_LONG   (0xffffffff)

const unsigned char NOMBRE_DE_BIT_DANS_UN_BYTE = 8;
const unsigned char TAILLE_CHAR = sizeof(unsigned char);

const unsigned long TAILLE_DES_BLOCS_MEMOIRE = 1024*1024;
const unsigned short NOMBRE_DE_BLOC_MEMOIRE = (MAX_UNSIGNED_LONG + 1) / (TAILLE_DES_BLOCS_MEMOIRE * NOMBRE_DE_BIT_DANS_UN_BYTE);

const unsigned char POSITION_DEBUT_FICHIER = 0;
const unsigned char OFFSET_DE_FIN_DE_FICHIER = 0;

const unsigned long TAILLE_DES_TRANCHES_DE_MEMOIRE_SUR_LE_DISQUE = TAILLE_DES_BLOCS_MEMOIRE * NOMBRE_DE_BLOC_MEMOIRE;

using namespace std;

int main(int argc, char *argv[])
{
    char* monTableau = new char[TAILLE_DES_BLOCS_MEMOIRE];
    
    for(unsigned long i = 0; i < TAILLE_DES_BLOCS_MEMOIRE; i++)
    {
        monTableau[i] = 0;
    }
    
    fstream monFichier("data.bin", ios::in | ios::out | ios::binary);
    
    unsigned long long offset = monFichier.tellg();
    
    for(unsigned short i = 0; i < NOMBRE_DE_BLOC_MEMOIRE; i++)
    {
        monFichier.write(monTableau, TAILLE_DES_BLOCS_MEMOIRE);
    }
    
    delete[] monTableau;
    
    monTableau = NULL;
    
    bitset<NOMBRE_DE_BIT_DANS_UN_BYTE> monBitSet;
    
    bool nEstPasPasseParLa;
    
    unsigned long long nombreDeBitsModifies = 0;
    
    unsigned char nombreDeTranchesMemoiresConsecutivesSurLeDisque = 1;
    
    bool trancheMemoireNonAjoutee;
    
    for(unsigned long m_ulRandomSeed = 0; nombreDeBitsModifies <= MAX_UNSIGNED_LONG; m_ulRandomSeed++)
    {
        if(monTableau)
        {
        }
        else
        {
            monTableau = new char;
        }
        
        nEstPasPasseParLa = true;
        
        for(unsigned char i = 0; i < nombreDeTranchesMemoiresConsecutivesSurLeDisque; i++)
        {
            monFichier.seekg(offset + i*TAILLE_DES_TRANCHES_DE_MEMOIRE_SUR_LE_DISQUE + m_ulRandomSeed / NOMBRE_DE_BIT_DANS_UN_BYTE);
            monFichier.read(monTableau, TAILLE_CHAR);
            
            monBitSet = reinterpret_cast<bitset<NOMBRE_DE_BIT_DANS_UN_BYTE>*>(monTableau);
        
            if(monBitSet[m_ulRandomSeed % NOMBRE_DE_BIT_DANS_UN_BYTE])
            {
                nEstPasPasseParLa = false;
            }
        }
        
        if(nEstPasPasseParLa)
        {
            monBitSet[m_ulRandomSeed % NOMBRE_DE_BIT_DANS_UN_BYTE] = 1;
            
            delete monTableau;
            monTableau = reinterpret_cast<char*>(&monBitSet);
            
            monFichier.seekp(offset + m_ulRandomSeed / NOMBRE_DE_BIT_DANS_UN_BYTE);
            monFichier.write(monTableau, TAILLE_CHAR);
            
            nombreDeBitsModifies++;
        }
        
        while(nEstPasPasseParLa)
        {
            m_ulRandomSeed = (RANDOM_A * m_ulRandomSeed) + RANDOM_C;
            
            trancheMemoireNonAjoutee = true;
            
            for(unsigned char i = 0; i < nombreDeTranchesMemoiresConsecutivesSurLeDisque && trancheMemoireNonAjoutee; i++)
            {
                monFichier.seekg(offset + i*TAILLE_DES_TRANCHES_DE_MEMOIRE_SUR_LE_DISQUE + m_ulRandomSeed / NOMBRE_DE_BIT_DANS_UN_BYTE);
                monFichier.read(monTableau, TAILLE_CHAR);
            
                monBitSet = reinterpret_cast<bitset<NOMBRE_DE_BIT_DANS_UN_BYTE>*>(monTableau);
            
                if(monBitSet[m_ulRandomSeed % NOMBRE_DE_BIT_DANS_UN_BYTE])
                {
                    nEstPasPasseParLa = false;
                    
                    delete monTableau;
                    monTableau = new char[TAILLE_DES_BLOCS_MEMOIRE];
                    
                    for(unsigned long i = 0; i < TAILLE_DES_BLOCS_MEMOIRE; i++)
                    {
                        monTableau[i] = 0;
                    }
                    
                    monFichier.seekp(OFFSET_DE_FIN_DE_FICHIER, ios::end);
                    
                    for(unsigned short i = 0; i < NOMBRE_DE_BLOC_MEMOIRE; i++)
                    {
                        monFichier.write(monTableau, TAILLE_DES_BLOCS_MEMOIRE);
                    }
                    
                    nombreDeTranchesMemoiresConsecutivesSurLeDisque++;
                
                    delete[] monTableau;
                
                    monTableau = NULL;
                    
                    trancheMemoireNonAjoutee = false;
                }
            }
            
            if(nEstPasPasseParLa)
            {
                monBitSet[m_ulRandomSeed % NOMBRE_DE_BIT_DANS_UN_BYTE] = 1;
                
                delete monTableau;
                monTableau = reinterpret_cast<char*>(&monBitSet);
                
                monFichier.seekp(offset + m_ulRandomSeed / NOMBRE_DE_BIT_DANS_UN_BYTE);
                monFichier.write(monTableau, TAILLE_CHAR);
                
                nombreDeBitsModifies++;
            }
        }
    }
    
    system("PAUSE");
    return EXIT_SUCCESS;
}


I have problems with lines 75 and 107, with which I get a "non-lvalue in assignment" error. Everything else seems just fine... I might know what it is but I thought you guys could give us a hint on how to use reinterpret_cast properly.

Thanks,
AeonFlux
LB (13399)
You can not do what you are trying to do. The compilation error is a syntax error (you need to reference the pointer), but the real problem is that you're trying to reinterpret_cast with non-POD types.

AeonFlux1212 wrote:
how to use reinterpret_cast properly.
Impossible - by design, there is no proper way to use it.
Bourgond Aries (415)
monBitSet is not a pointer.
AeonFlux1212 (125)
Yes you guys are right I think I fixed it ... I made monBitSet a pointer to a new bitset<NOMBRE_DE_BIT_DANS_UN_BYTE>.... the rest follows...

Thanks a lot!
AeonFlux




... L B what is a non-POD type?
AeonFlux1212 (125)
Hello again... after a lot of testing and debugging I figured out that casting a char* to a bitset<>* and vice-versa simply doesn't work... like L B mentionned earlier... I mean it works, but you can't really use the results like I wanted to use them.

So I had to make my own charTObits and bitsTOchar functions, and now everything seems to work just fine... :-)

Thanks for the help, reply if you have any questions.

AeonFlux
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