设计共享内存系统V.

Question

我需要一个共享内存，它应该有2个字段 mh_data标题; 和 任何类型任何长度的可变数据字段

我使用了代码 - ＆gt;

   #include <stdio.h>
 #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>
#include <sys/mman.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
//#include <conio.h>


#define ERROR  -1
#define SUCCESS 0


typedef           char    int8;
typedef unsigned int   u_int32;
typedef unsigned short u_int16;
typedef int error_code;


typedef union { 
        u_int32 group_user;             /* group/user numbers */
        struct {
                u_int16 grp;                    /* group number */
                u_int16 usr;                    /* user number  */
        } grp_usr;
} owner_id;

typedef struct mh_com {
        u_int16
                m_sync,                 /* sync bytes                                                                   */
                m_sysrev;               /* system revision check value                                          */
        u_int32
                m_size;                 /* module size                                                                          */
        owner_id
                m_owner;                /* group/user id                                                                        */
        u_int32
                m_name;                 /* offset to module name                                                        */
        u_int16
                m_access,               /* access permissions                                                           */
                m_tylan,                /* type/lang                                                                            */
                m_attrev,               /* attributes/revision                                                          */
                m_edit;                 /* edition                                                                                      */
        u_int32
                m_needs,                /* module hardware requirements flags  (reserved)       */
                m_share,                /* shared data offset                                                           */
                m_symbol,               /* symbol table offset                                                          */
                m_exec,                 /* offset to execution entry point                                      */
                m_excpt,                /* offset to exception entry point                                      */
                m_data,                 /* data storage requirement                                                     */
                m_stack,                /* stack size                                                                           */
                m_idata,                /* offset to initialized data                                           */
                m_idref,                /* offset to data reference lists                                       */
                m_init,                 /* initialization routine offset                                        */
                m_term;                 /* termination routine offset                                           */
        u_int32
                m_dbias,                /* data area bias                                                                       */
                m_cbias;                /* code area bias                                                                       */
        u_int16
                m_ident;                /* ident code for ident program                                         */
        char
                m_spare[8];             /* reserved bytes                                                                       */
        u_int16
                m_parity;               /* header parity                                                                        */
        int8    m_shm_obj[256];
} mh_com, *Mh_com;

typedef mh_com mh_data;

error_code _os_datmod(
                     const char *mod_name,
                     u_int32 sz,
                     u_int16 *attr_rev,
                     u_int16 *type_lang,
                     u_int32 perm,
                     void **mod_data,
                     mh_data **mod_head)
{
        struct datmod
        {
                mh_data header;
                int size;
                /*union Data
                {
                        char str[sz];
                }data;*/
                char data[sz];
                //void* dataPtr;
        };

        int fd;
        int len;
        struct stat shm_mod_stat;
        void *addr;
        len = strlen(mod_name);
        /* Open new POSIX shared memory object */
        if ((fd = shm_open(mod_name, O_RDWR |O_CREAT, /* mode_t */ 0666)) == -1)
        {
                /* TODO: If mod_name path is invalid, then return EOS_PNNF */
                return ERROR;
        }



        if(ftruncate(fd, sizeof(struct datmod))==-1)
        {
               perror("ftruncate");
               shm_unlink(mod_name);
               return ERROR;
        }

        /* do mmap */
        addr = (struct datmod *)mmap(NULL, sizeof(struct datmod), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

        if (addr == MAP_FAILED)
        {
                shm_unlink(mod_name);
                return ERROR;
        }

        ((struct datmod *)addr)->size = sz;

        /* mmaped address */
        *mod_data = &(((struct datmod *)addr)->data);
        *mod_head = &(((struct datmod *)addr)->header);
        //memset((((union Data*)(*mod_data))->str),0,sz);
        memset(((*(char **)mod_data)),0,sz);

        //(*mod_head)->m_shm_obj = (int8 *) malloc(len + 1);
        memcpy(&((*mod_head)->m_shm_obj), (mod_name), len);
        (*mod_head)->m_shm_obj[len] = '\0';

        close(fd);

        return SUCCESS;
}



int main()
{
        void* data;
        mh_data *  header;
        char str[] = "/Sandeep";
        _os_datmod(str,50,0,0,0,&data, &header);
        struct DATA
        {
                int i;
                float j;
        }*dat;
        dat = (struct DATA *)(data);
        dat->i = 5;
        dat->j = 4.2;
        //strcpy((char*)data , str);
        int res = fork();
        if(res==0)
        {
                _os_datmod(str,50,0,0,0,&data, &header);
                dat = (struct DATA *)(data);
                printf("i=%d,j=%f\n",dat->i,dat->j);
                //printf("%s",(char *)data);
        }
        printf("hello world\n");
}

但它会打印出来 你好，世界 I = 0，J = 0.000000 你好世界

我还需要改变

 struct datmod
        {
                mh_data header;
                int size;
                /*union Data
                {
                        char str[sz];
                }data;*/
                char data[sz];
                //void* dataPtr;
        };

这样 数据字段可以扩展到任何长度和任何类型。 所以，请建议