Store data from struct in lists of variable size in C -

i want use mpi in project. in order send data processor, first have store particle data in list.

these lists can have variable size. want save data of struct:

typedef struct {         double    x[dim];         double    v[dim];         double    a[dim];         double    m; } particle; 

into list 'plist'. additionally want save size of list in plistsize:

typedef struct{     double **plist;     int plistsize; } particlelist; 

i still newbie in c task somehow difficult me.

so far did following:

#include <stdlib.h> #include <stdio.h>  #define dim 2  typedef struct{     double **plist;     int plistsize; } particlelist;  typedef struct {         double                x[dim];         double                v[dim];         double                a[dim];         double                 m; } particle;  void sendpar(int *n, int npr, particle *p){      // allocate memory particlelist     particlelist *pl = malloc(sizeof(pl)*npr);      // allocate memory plistsize -> not work     //for(int k=0; k<npr; k++){     //    pl->plistsize[k] = malloc(sizeof(int*));     //}      // allocate memory every list     for(int k=0; k<npr; k++){         pl->plist[k] = malloc(sizeof(double*) * n[k]);     }      // write data list.     for(int k=0; k<npr; k++){         for(int l=0; l<n[k]; l++){             int = 0;             for(int d=0; d<dim; d++){                 pl->plist[k][i] = p[k].x[d];                 i++;             }             for(int d=0; d<dim; d++){                 pl->plist[k][i] = p[k].v[d];                 i++;             }             for(int d=0; d<dim; d++){                 pl->plist[k][i] = p[k].a[d];                 i++;             }             pl->plist[k][i] = p[k].m;         }    // pl->plistsize[k] = n[k];     }      // free memory     free(pl); }  int main(){     // number of processors     int npr = 3;      // number of particles     int np = 3;      // allocate memory particles     particle *p = malloc(sizeof(p)*np);     for(int k=0; k<np; k++){         for(int d=0; d<dim; d++){             p[k].x[d] = 1000*k+100*d;             p[k].v[d] = 10000*k+1000*d;             p[k].a[d] = 10*k+d;         }         p[k].m = 100000+k;     }      // size of lists, in case every list has same length     int n[npr];     n[0] = 10;     n[1] = 10;     n[2] = 10;      sendpar(n, npr, p);      // free memory     free(p); } 

i seg fault error. did wrong here:

// allocate memory particlelist particlelist *pl = malloc(sizeof(pl)*npr);  // allocate memory every list for(int k=0; k<npr; k++){     pl->plist[k] = malloc(sizeof(double*) * n[k]); } 

additionally not able allocate memory plistsize. error warning: assignment makes integer pointer without cast. see why?