Btukfyl

Hi i want to use multidimensional very large array. I tried following code. It compiles but when i execute it it gives me segmentation fault error.

'int NT = 35; int NX = 25; int NY = 25; int NZ = 25;

double dt = 0.1; double dx = 0.5; double dy = 0.5; double dz = 0.5;



double PosT[NT]; 

double PosX[NX]; double PosY[NY]; double PosZ[NZ];



for(int i=0;i<NT;i++)

    PosT[i] = i*dt+dt;

for(int i=0; i<NX;i++)

    PosX[i] = dx*i;

for(int i=0; i<NY;i++)

    PosY[i] = dy*i;

for(int i=0; i<NZ;i++)

    PosZ[i] = dz*i;



double* b_x=(double*)malloc(NX*NY*NZ*sizeof(double));

double* b_y=(double*)malloc(NX*NY*NZ*sizeof(double));

double** B=(double**)malloc(NX*NY*NZ*NT*sizeof(double*));



if(b_x==NULL||b_y==NULL){

    cout<<"Malloc space error!"<<endl;

    return 0;

}

    for(int ix=0;ix<NX;ix++){

        for(int iy=0;iy<NY;iy++){

            for(int iz=0;iz<NZ;iz++){

                int position=ix*NY*NZ+iy*NZ+iz; 

                b_x[position] =0.;

                b_y[position] =0.;

            }

        }

    }'

but when i work in below part then i got segmentation error, my codes next part is following lines which include 2d arrays. and this 2d array is very large ,
perhaps due to this i am getting segmentation error

    'if(B==NULL){

    cout<<"Malloc space error!"<<endl;

    return 0;

    }

    cout<<"work"<<endl;

        for(int ix=0;ix<NX;ix++){

        for(int iy=0;iy<NY;iy++){

            for(int iz=0;iz<NZ;iz++){

                int position=ix*NY*NZ+iy*NZ+iz;

                for(int it=0;it<NT;it++){               

                B[position][it]=0.;

            }

        }

    }

}

 cout<<"not working"<<endl;' 

so code between work and not working has problem which causes segmentation error. Any solutions for this.

int NT = 35; int NX = 25; int NY = 25; int NZ = 25;

For simplicity, let's change all of these to NT=NX=NY=NZ=2. This line:

double** B=(double**)malloc(NX*NY*NZ*NT*sizeof(double*));

would then allocate space for 16 pointers. On the first iteration through the loops, this line:

B[position][it]=0.;

would be equivalent to:

double *tmp = B[0];  // Load uninitialized pointer from B[0]

tmp[0] = 0.0;        // Dereference uninitialized pointer to store something.

It shouldn't be at all surprising that this code results in a SIGSEGV.

What you probably meant:

double *B = malloc(NX*NY*NZ*NT*sizeof(double));

for(int ix = 0; ix < NX; ix++) {

  for(int iy = 0; iy < NY; iy++) {

    for(int iz = 0; iz < NZ; iz++) {

       for(int it = 0; it < NT; it++) {

         int position = NT * (NZ * (NY * ix + iy) + iz) + it;

         B[position] = 0.0;

       }

    }

  }

}