shm_creat.cpp

linux环境下 共享内存的简单使用

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <ctype.h>

#define SHMSIZE 1024

int open_shm(key_t key_val)
{
  int shmid;
  if((shmid=shmget(key_val, SHMSIZE, IPC_CREAT|IPC_EXCL|0666))==-1)
  {
    printf("Shared memory segment exists. \n");
    if((shmid=shmget(key_val, SHMSIZE, 0))==-1)
    {
      perror("shmget");
      exit(1);
    } 
  }
  else
  {
    printf("Creating new shared memory segment. \n");
  }
  
  return shmid;
}

void writeshm(int shmid, void* segptr, char * text)
{
  printf("write text length: %d \n", strlen(text));
  strcpy((char*)segptr, text);
  strncpy((char*)segptr, text, strlen(text));
 // memcpy(segptr, "bagbao", sizeof(text));
  printf("Done...");
}


void readshm(int shmid, void* segptr)
{
   printf("segptr:%s \n", (char*)segptr); 
}

void removeshm(int shmid)
{
  shmctl(shmid, IPC_RMID, 0);
  printf("Shared memory deleted \n");
}

void changemode(int shmid, char* mode)
{
  struct shmid_ds myshm_ds;

  shmctl(shmid, IPC_STAT, &myshm_ds);

  printf("Old permissions were: %o \n", myshm_ds.shm_perm.mode);
  
  
  sscanf(mode,"%o", &myshm_ds.shm_perm.mode);
  
  shmctl(shmid, IPC_SET, &myshm_ds);

  printf("New permissions are : %o \n", myshm_ds.shm_perm.mode);

}


void usage()
{
  fprintf(stderr,"shmtoo -A utility for tinkering with shared memory \n");
  fprintf(stderr,"shmtool (w)rite <text> \n");
  fprintf(stderr,"shmtool (w)rite <text> \n");
  fprintf(stderr,"shmtool (r)ead <text> \n");
  fprintf(stderr,"shmtool (d)elete shm  \n");
  fprintf(stderr,"shmtool (m)ode change \n");
  exit(1);
}


int main(int argc, char ** argv)
{
  key_t key;
  int shmid;
  void* segptr;

  printf("argc =%d \n ", argc);

  if(argc==1) usage();

  key=ftok(".", 'S');

  if((shmid=open_shm(key))==-1)
  {
    perror("shmget");
    exit(1);
  } 

  printf("Creat shm ok \n");  
  
  if((segptr=shmat(shmid, 0, 0))==(void *)-1) 
  {
    perror("shmat");
    exit(1);
  }
  
  printf("shmat  ok \n");

  switch(tolower(argv[1][0]))
  {
    case 'w':
         writeshm(shmid, segptr, argv[2]);
         break;
    case 'r':
         readshm(shmid, segptr);
         break;
    case 'd':
         removeshm(shmid);
         break;
    case 'm':
         changemode(shmid, argv[2]);
         break;
    default:
         usage();

   }
   return 1;
}