c - Using shared memory with matrices -

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i want create matrix in shared memory segment. in second programme can read taillex, tailley matrix has '0' in value. create matrix in function initialisersegmem , values ok... have problem pointers...

my struct mem_share:

typedef struct mem_partage{     int** carte;     int tailley;     int taillex; }mem_share;  mem_share initialiserdonneemem(grille* g){     mem_share mem_share_carte;     int x = g->taillex;     int y = g->tailley;     int i,j;     mem_share_carte.carte = malloc(y*sizeof(int*));     for(i=0;i < y;i++){         mem_share_carte.carte[i] = malloc(x*sizeof(int));     }      mem_share_carte.carte = g->carte;     mem_share_carte.tailley = y;     mem_share_carte.taillex = x;      return mem_share_carte; }  void initialisersegmem(mem_share *mem_share_carte){     int shmid,id_memoire,i,j;        int test = 100;        int *adresse_mem;     key_t cle;     cle = 9999;     /* creation of shared memory segment */     if(shmget(cle,(int) sizeof(mem_share) ,ipc_creat | ipc_excl | 0777)== -1) {         printf("erreur : segment de mémoire partagée existant");     }     /*on attache le segment notre espace memoire */     id_memoire = shmget(cle,0,0);     adresse_mem = shmat(id_memoire,null,0);     /* les 2premiers int seront les tailles y et x*/     printf("tailley %d zzzz",mem_share_carte->tailley);     memcpy(adresse_mem,&mem_share_carte->tailley,sizeof(int));     adresse_mem+=sizeof(int);     memcpy(adresse_mem,&mem_share_carte->taillex,sizeof(int));     adresse_mem+=sizeof(int);      for(i=0;i<mem_share_carte->tailley;i++){         printf("\n");             for(j=0;j<mem_share_carte->taillex;j++){                 memcpy(adresse_mem,&(mem_share_carte->carte[i][j]),sizeof(int));             adresse_mem+=sizeof(int);             }     } }

in second program i'm trying read shared memories:

int shmid,tailley,taillex,y,x;  int *adresse_mem; key_t cle; /* on recupere la cle du segment */ cle = 9999; if ((shmid = shmget(cle, 0, 0666)) < 0) {     perror("shmget");     exit(1);     } /*     * on attache le segment notre espace memoire */ if ((adresse_mem = shmat(shmid, null, 0)) == (char *) -1) {     perror("shmat");     exit(1); } /* * on lit le segment : *  - on recupe la taille y *  - puis la taille x *  - puis la carte */ memcpy(&tailley,adresse_mem,sizeof(int)); adresse_mem+=sizeof(int); printf("tailley %d",tailley); memcpy(&taillex,adresse_mem,sizeof(int)); printf("taillex %d",taillex); adresse_mem+=sizeof(int);  int** carte; carte = malloc(tailley*sizeof(int*));  for(y=0;y<tailley;y++){     carte[y] = malloc(taillex*sizeof(int));     for(x=0;x>taillex;x++){         memcpy(&carte[y][x],adresse_mem,sizeof(int));         adresse_mem+=sizeof(int);     } } /*     affichage de la carte */ for(y = 0;y<tailley;y++){     printf("\n");     for(x = 0;x<taillex;x++){         printf("%d ",carte[y][x]);     } }

by way, in first program must update matrix in shared memories, can call initialisersegmem new matrix?

a simple example code. child , parent shared 2d vector using system v shared memory segment. sizeelement used offset estimation when data type change. here double used. not error handling on functions' returned code.

#include <stdio.h> #include <unistd.h> #include <sys/shm.h> #include <sys/stat.h> #include <wait.h>  unsigned int sizeof_dm(int rows, int cols, size_t sizeelement){     size_t size = rows * (sizeof(void *) + (cols * sizeelement));     return size; }  void create_index(void **m, int rows, int cols, size_t sizeelement){     int i;       size_t sizerow = cols * sizeelement;     m[0] = m+rows;     for(i=1; i<rows; i++){               m[i] = (m[i-1]+sizerow);     } }  void print_matriz(double **matrix, int rows, int cols){     printf("\n");         for(int i=0; i<rows; i++){             for(int j=0; j<cols; j++)                 printf("%.2f\t",matrix[i][j]);             printf("\n");         } }  int main(int argc, char **argv){      double **matrix;     int cols = 10, rows = 5, shmid;      size_t sizematrix = sizeof_dm(rows,cols,sizeof(double));     shmid = shmget(ipc_private, sizematrix, ipc_creat|0600);         matrix = shmat(shmid, null, 0);      create_index((void*)matrix, rows, cols, sizeof(double));       if(fork()){         int pos=0;         for(int i=0; i<rows; i++){             for(int j=0; j<cols; j++)                 matrix[i][j] = pos++;         }                wait(null);          print_matriz(matrix, rows, cols); //verify child's write         shmdt(matrix);         shmctl(shmid, ipc_rmid, 0);     }     else{            sleep(3); //avoid race condition         print_matriz(matrix, rows, cols);         matrix[2][2] = -99.99; //writing test child         shmdt(matrix);     }     return 0; }

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