标准I/O-2-文件结束或出错,EOF,fgetc,feof,ferror,clearerr,rewind（未完）
参考博文：
http://bbs.chinaunix.net/thread-233220-1-1.html
http://www.cnitblog.com/guopingleee/archive/2009/01/29/54047.html
http://hi.baidu.com/qq630727668%BA%CD51wangying19881118/blog/item/6bc6493395c80f4bad4b5fa3.html
http://www.cnblogs.com/xbspring/archive/2009/01/08/1371696.html（文本文件与二进制文件）
http://www.cnblogs.com/tenghoo/archive/2008/06/01/1211663.html（原码、补码和反码）
----------FILE定义
1、网上流传的版本
/* <stdio.h> */
typedef struct {
int level; /* fill/empty level of buffer */
unsigned flags; /* File status flags */
char fd; /* File descriptor */
unsigned char hold; /* Ungetc char if no buffer */
int bsize; /* Buffer size */
unsigned char _FAR *buffer; /* Data transfer buffer */
unsigned char _FAR *curp; /* Current active pointer */
unsigned istemp; /* Temporary file indicator */
short token; /* Used for validity checking */
} FILE; /* This is the FILE object */
2、VS2008
/* <stdio.h> */
struct _iobuf {
char *_ptr;//文件内部指针
int _cnt;
char *_base;
int _flag;
int _file;
int _charbuf;
int _bufsiz;
char *_tmpfname;
};
typedef struct _iobuf FILE;
3、Linux GCC
/* <libio.h> */
struct _IO_FILE {
int _flags; /* High-order word is _IO_MAGIC; rest is flags. */
#define _IO_file_flags _flags
/* The following pointers correspond to the C++ streambuf protocol. */
/* Note: Tk uses the _IO_read_ptr and _IO_read_end fields directly. */
char* _IO_read_ptr; /* Current read pointer */
char* _IO_read_end; /* End of get area. */
char* _IO_read_base; /* Start of putback+get area. */
char* _IO_write_base; /* Start of put area. */
char* _IO_write_ptr; /* Current put pointer. */
char* _IO_write_end; /* End of put area. */
char* _IO_buf_base; /* Start of reserve area. */
char* _IO_buf_end; /* End of reserve area. */
/* The following fields are used to support backing up and undo. */
char *_IO_save_base; /* Pointer to start of non-current get area. */
char *_IO_backup_base; /* Pointer to first valid character of backup area */
char *_IO_save_end; /* Pointer to end of non-current get area. */
struct _IO_marker *_markers;
struct _IO_FILE *_chain;
int _fileno;
int _blksize;
_IO_off_t _offset;
#define __HAVE_COLUMN /* temporary */
/* 1+column number of pbase(); 0 is unknown. */
unsigned short _cur_column;
char _unused;
char _shortbuf[1];
/* char* _save_gptr; char* _save_egptr; */
_IO_lock_t *_lock;
};
/* <stdio.h> */
#include <libio.h>
typedef struct _IO_FILE FILE;
----------函数原型及作用
int feof(FILE *stream);The function feof() tests the end-of-file indicator for the stream pointed to by stream, returning non-zero if it is set.The end-of-file indicator can only be cleared by the function clearerr().
说明：测试文件内部指针是否到达文件末尾
int ferror(FILE *stream);The function ferror() tests the error indicator for the stream pointed to by stream, returning non-zero if it is set.The error indicator can only be reset by the clearerr() function.
说明：测试文件内部指针是否出错
int fgetc(FILE *stream);reads the next character from stream and returns it as an unsigned char cast to an int, or EOF on end of file or error.
MSDN中的一段话：use feof or ferror to distinguish between an error and an end-of-file condition（用feof和ferror来区分end-of-file和error两种情况）
说明：返回值有两类，一类是获取到的字符（被转化为int型了），二类是返回-1(EOF)（见下面的【重点讨论】）
void clearerr(FILE *stream);The function clearerr() clears the end-of-file and error indicators for the stream pointed to by stream.
说明：清除end-of-file indicator和error indicator。【重点】FILE结构体里有记录文件内部指针到达文件末尾和出错的标志变量，当用fgetc()处理文件时，如果到达文件末尾或出错，相应的标志变量会置于出错状态，clearerr()的作用是将这两个标志变量置于正常状态
void rewind(FILE *stream);（下面这段摘自MSDN）
The rewind function repositions the file pointer associated with stream to the beginning of the file. A call to rewind is similar to
(void) fseek( stream, 0L, SEEK_SET );
However, unlike fseek, rewind clears the error indicators for the stream as well as the end-of-file indicator. Also, unlike fseek, rewind does not return a value to
indicate whether the pointer was successfully moved.
说明：rewind()的作用不但是将文件内部指针回置开始处，而且还会清除end-of-file indicator和error indicator
----------如何判断一个文件内部指针已到达文件末尾？——EOF和feof()
****以下都以fgetc()读取为例
1、feof()判断
对文本文件和二进制文件均使用，但须注意一点，如下：
----例1（错误）（谭浩强的书中是这样的）
char c;
while(!feof(fp))
{
c = fgetc(fp);
printf("%X\n", c);
}当fgetc()读到文件末尾时，还会输出一次，即0xFF(-1)
----例2（正确）
char c;
c = fgetc(fp);
while(!feof(fp))
{
printf("%X\n", c);
c = fgetc(fp);
}
2、EOF判断
（未完待续）
----------补充——原码、反码、补码
对于char型数据：char ch = oxFF;
ch的二进制形式是多少？-1
(FF)H --> (1111,1111)B——这是补码形式 --> (1000,0001)B——这是原码形式，即-1
对于int型数据：int a = 0xFF;
a的二进制形式是多少？255
注：gcc中int型占4个byte
(FF)H --> (00000000,00000000,00000000,11111111)——由于最高位为0，即正数，正数的原码和补码相同
那int a = -1;的十六进制是多少？0xFFFFFFFF