实例9-18.c

Linux下C语言编程例子

#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
typedef struct{
	char name[4];
	int  age;
}people;
main(int argc, char** argv)
{
	int fd,i;
	int pagesize,offset;
	people *p_map;
	
	pagesize = sysconf(_SC_PAGESIZE);
	printf("pagesize is %d\n",pagesize);
	fd = open(argv[1],O_CREAT|O_RDWR|O_TRUNC,00777);
	lseek(fd,pagesize*2-100,SEEK_SET);
	write(fd,"",1);
	offset = 0;	/*此处offset = 0编译成版本1；offset = pagesize编译成版本2*/
	p_map = (people*)mmap(NULL,pagesize*3,PROT_READ|PROT_WRITE,MAP_SHARED,fd,offset);
	close(fd);
	
	for(i = 1; i<10; i++)
	{
		(*(p_map+pagesize/sizeof(people)*i-2)).age = 100;
		printf("access page %d over\n",i);
		(*(p_map+pagesize/sizeof(people)*i-1)).age = 100;
		printf("access page %d edge over, now begin to access page %d\n",i, i+1);
		(*(p_map+pagesize/sizeof(people)*i)).age = 100;
		printf("access page %d over\n",i+1);
	}
	munmap(p_map,sizeof(people)*10);
}