Linux下文件操作

代码如下：

代码很简单，刚开始一直读取不到数据，原来是在写完后，偏移地址指针处在文件末尾，则可用lseek函数使指针指向文件开头。
/*****
author:mlkk
date:2017.0.25
function:test the lseek
*****/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#define  Size   20

int  main(void)
{

int fd;

unsigned char i;

int ret;

unsigned  char *W_buf = NULL;

unsigned  char *R_buf = NULL ; 

char *dev_mlkk = "/dev/test.txt";

fd = open(dev_mlkk,  O_CREAT | O_RDWR | O_SYNC);

if (fd < 0)

{

printf(" open %s failure .\n",dev_mlkk);

return -1;

}

W_buf = (unsigned  char *)malloc(Size * sizeof( unsigned char));

R_buf = (unsigned  char *)malloc(Size * sizeof( unsigned char));

for (i=0; i < Size; i++)

W_buf[i] = i;

printf("open successfull .\n");

ret = write(fd, W_buf, Size );

printf("write %d .\n", ret);

lseek(fd, 0, SEEK_SET); 

ret =  read(fd, R_buf, Size);

if (ret > 0)

{

printf("read :%d :\n", ret);

for(i = 0; i < Size; i++)

{

printf("%d: %d \n",i,R_buf[i]);

}

}

else

{

printf("read  failed .\n");

return -1;

}

free(W_buf);

free(R_buf);

W_buf = NULL;

R_buf = NULL;

close(fd);

}