write.c

源码包中是我在学习Linux进程间通信时所写的关于五种通信方式（管道

/* 
 * write shared memory
*/

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

#define	MAPPED_FILENAME		"/tmp/test.mmap.1"

int main()
{	
	int 	fd;

	/* step 1, open file, get a fd */
	if( (fd = open(MAPPED_FILENAME, O_RDWR|O_CREAT|O_EXCL, 0666)) < 0 )
	{
		perror( "open error" );
		exit(1);
	}

	off_t	offset = 1024;

	/* step 2, create a hole file */
	if( lseek(fd, offset, SEEK_SET) == (off_t)-1 )
	{
		perror( "lseek failed" );
		close( fd );
		exit(1);
	}

	ssize_t	n;

	if( (n = write(fd, " ", 1)) < 0 )
	{
		perror( "write error" );
		exit(1);
	}

	void	*p;
	
	/* step 3, mmap(), get a pointer */
	if( (p = mmap(NULL, 1024, PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED )
	{
		perror( "mmap error" );
		close( fd );
		exit(1);
	}
	
	close( fd );

	fprintf( stdout, "mapped file to memory, size = %d\n", 1024 );
	
	/* read/write on shared memory */
	char	*banner = "hello, world.";

	memcpy( p+256, banner, strlen(banner) );

	pause();

	return 0;
}