在C++中怎样实现对数据文件的指定数据类型的指定字节长度的数据读取啊?

函数名: fread
功 能: 从一个流中读数据
用 法: int fread(void *ptr, int size, int nitems, FILE *stream);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
FILE *stream;
char msg[] = "this is a test";
char buf[20];

if ((stream = fopen("DUMMY.FIL", "w+"))
== NULL)
{
fprintf(stderr,
"Cannot open output file.\n");
return 1;
}

/* write some data to the file */
fwrite(msg, strlen(msg)+1, 1, stream);

/* seek to the beginning of the file */
fseek(stream, SEEK_SET, 0);

/* read the data and display it */
fread(buf, strlen(msg)+1, 1, stream);
printf("%s\n", buf);

fclose(stream);
return 0;
}

你想要读两个字节的话：
fread(buf, 2, i, stream);
i+=2;