my_rwl.c

《Linux C编程实战》人民邮电出版社

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

/*自定义的错误处理函数*/
void my_err(const char * err_string, int line)
{
	fprintf(stderr, "line:%d  ", line);
	perror(err_string);
	exit(1);
}

/*自定义的读数据函数*/
int my_read(int fd)
{
	int		len;
	int		ret;
	int		i;
	char	read_buf[64];

	/*获取文件长度并保持文件读写指针在文件开始处*/
	if (lseek(fd, 0, SEEK_END) == -1) {
		my_err("lseek", __LINE__);
	}
	if ((len = lseek(fd, 0, SEEK_CUR)) == -1) {
		my_err("lseek", __LINE__);
	}
	if ((lseek(fd, 0, SEEK_SET)) == -1) {
		my_err("lseek", __LINE__);
	}
	
	printf("len:%d\n", len);
	/*读数据*/
	if ((ret = read(fd, read_buf, len)) < 0) {
		my_err("read", __LINE__);
	}
	
	/*打印数据*/
	for (i=0; i<len; i++) {
		printf("%c", read_buf[i]);
	}
	printf("\n");

	return ret;
}

int main()
{
	int	fd;
	char 	write_buf[32] = "Hello World!";

	/*在当前目录下创建文件example_63.c*/
	//if ((fd = creat("example_63.c", S_IRWXU)) == -1) {
	if ((fd = open("example_63.c", O_RDWR|O_CREAT|O_TRUNC, S_IRWXU)) == -1) {
		my_err("open", __LINE__);
	} else {
		printf("create file success\n");
	}
	
	/*写数据*/
	if (write(fd, write_buf, strlen(write_buf)) != strlen(write_buf)) {
		my_err("write", __LINE__);
	}
	my_read(fd);

	/*演示文件的间隔*/
	printf("/*--------------------*/\n");
	if (lseek(fd, 10, SEEK_END) == -1) {
		my_err("lseek", __LINE__);
	}
	if (write(fd, write_buf, strlen(write_buf)) != strlen(write_buf)) {
		my_err("write", __LINE__);
	}
	my_read(fd);
	
	close(fd);
	return 0;
}