shmread.c

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/shm.h>


#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>


#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)




typedef struct stu
{
int age;
char name[32];
} STU;


int main(int argc, char *argv[])
{
int shmid;
shmid = shmget(1234, 0, 0);
if (shmid == -1)
ERR_EXIT("shmget");


STU *p;
p = shmat(shmid, NULL, 0);
if (p == (void*)-1)
ERR_EXIT("shmat");


printf("name = %s age = %d\n", p->name, p->age);
memcpy(p, "quit", 4);


shmdt(p);
return 0;
}

shmwrite.c

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/shm.h>


#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>


#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)




typedef struct stu
{
int age;
char name[32];
} STU;


int main(int argc, char *argv[])
{
int shmid;
shmid = shmget(1234, sizeof(STU), IPC_CREAT | 0666);
if (shmid == -1)
ERR_EXIT("shmget");


STU *p;
p = shmat(shmid, NULL, 0);
if (p == (void*)-1)
ERR_EXIT("shmat");


strcpy(p->name, "lisi");
p->age = 20;




while (1)
{
if (memcmp(p, "quit", 4) == 0)
break;
}
shmdt(p);
shmctl(shmid, IPC_RMID, NULL);
return 0;
}

makefile:

.PHONY:clean all
CC=gcc
CFLAGS=-Wall -g
BIN=shmwrite shmread
all:$(BIN)
%.o:%.c
$(CC) $(CFLAGS) -c $< -o $@
clean:
rm -f *.o $(BIN)