在成功获取到key之后，就可以使用该key作为某种方法的进程间通信的key值，例如shmget共享内存的方式。
shmget的函数原型为
int shmget( key_t, size_t, flag);
在创建成功后，就返回共享内存的描述符。在shmget中使用到的key_t就是通过ftok的方式生成的
实例:
#include
#include
#include
#include
#include
#define SIZE 1024
extern int errno;
int main()
{
int shmid;
char *shmptr;
//创建共享内存
if((shmid = shmget(IPC_PRIVATE, SIZE, 0600)) < 0)
{
printf("shmget error:%s\n", strerror(errno));
return -1;
}
//将共享内存连接到 可用地址上
if((shmptr = (char*)shmat(shmid, 0, 0)) == (void*)-1)
{
printf("shmat error:%s\n", strerror(errno));
return -1;
}
memcpy(shmptr, "hello world", sizeof("hello world"));
printf("share memory from %lx to %lx, content:%s\n",(unsigned long)shmptr, (unsigned long)(shmptr + SIZE), shmptr);
//拆卸共享内存
if((shmctl(shmid, IPC_RMID, 0) < 0))
{
printf("shmctl error:%s\n", strerror(errno));
return -1;
}
}
多进程之间共享内存情况:
#include
#include
#include
#include
#include
#include
#include
#include
#define SIZE 1024
extern int errno;
int main()
{
int shmid;
char *shmptr;
key_t key;
pid_t pid;
if((pid = fork()) < 0)
{
printf("fork error:%s\n", strerror(errno));
return -1;
}
else if(pid == 0)
{
sleep(2);
if((key = ftok("/dev/null", 1)) < 0)
{
printf("ftok error:%s\n", strerror(errno));
return -1;
}
if((shmid = shmget(key, SIZE, 0600)) < 0)
{
printf("shmget error:%s\n", strerror(errno));
exit(-1);
}
if((shmptr = (char*)shmat(shmid, 0, 0)) == (void*)-1)
{
printf("shmat error:%s\n", strerror(errno));
exit(-1);
}
//memcpy(shmptr, "hello world", sizeof("hello world"));
printf("child:pid is %d,share memory from %lx to %lx, content:%s\n",getpid(), (unsigned long)shmptr, (unsigned long)(shmptr + SIZE
), shmptr);
printf("child process sleep 2 seconds\n");
sleep(2);
if((shmctl(shmid, IPC_RMID, 0) < 0))
{
printf("shmctl error:%s\n", strerror(errno));
exit(-1);
}
exit(0);
}
//parent
else
{
if((key = ftok("/dev/null", 1)) < 0)
{
printf("ftok error:%s\n", strerror(errno));
return -1;
}
if((shmid = shmget(key, SIZE, 0600|IPC_CREAT|IPC_EXCL)) < 0)
{
printf("shmget error:%s\n", strerror(errno));
exit(-1);
}
if((shmptr = (char*)shmat(shmid, 0, 0)) == (void*)-1)
{
printf("shmat error:%s\n", strerror(errno));
exit(-1);
}
memcpy(shmptr, "hello world", sizeof("hello world"));
printf("parent:pid is %d,share memory from %lx to %lx, content:%s\n",getpid(),(unsigned long)shmptr, (unsigned long)(shmptr + SIZE
), shmptr);
printf("parent process sleep 2 seconds\n");
sleep(2);
if((shmctl(shmid, IPC_RMID, 0) < 0))
{
printf("shmctl error:%s\n", strerror(errno));
exit(-1);
}
}
waitpid(pid,NULL,0);
exit(0);
}
输出为:
shmctl(shmid, IPC_RMID, 0)的作用是从系统中删除该恭喜存储段。因为每个共享存储段有一个连接计数(shmid_ds结构中的shm_nattch)，所以除非使用该段的最后一个进程终止与该段脱接，否则不会实际上删除该存储段。