我在VC++6.0里找到了<stdio.h> 这个头文件，里面有一大段代码，这到底是怎么看的？



/***
*stdio.h - definitions/declarations for standard I/O routines
*
*       Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       This file defines the structures, values, macros, and functions
*       used by the level 2 I/O ("standard I/O") routines.
*       [ANSI/System V]
*
*       [Public]
*
****/

#if     _MSC_VER > 1000
#pragma once
#endif

#ifndef _INC_STDIO
#define _INC_STDIO

#if     !defined(_WIN32) && !defined(_MAC)
#error ERROR: Only Mac or Win32 targets supported!
#endif


#ifdef  _MSC_VER
/*
 * Currently, all MS C compilers for Win32 platforms default to 8 byte
 * alignment.
 */
#pragma pack(push,8)
#endif  /* _MSC_VER */

#ifdef  __cplusplus
extern "C" {
#endif



/* Define _CRTIMP */

#ifndef _CRTIMP
#ifdef  _DLL
#define _CRTIMP __declspec(dllimport)
#else   /* ndef _DLL */
#define _CRTIMP
#endif  /* _DLL */
#endif  /* _CRTIMP */


/* Define __cdecl for non-Microsoft compilers */

#if     ( !defined(_MSC_VER) && !defined(__cdecl) )
#define __cdecl
#endif

/* Define _CRTAPI1 (for compatibility with the NT SDK) */

#ifndef _CRTAPI1
#if    _MSC_VER >= 800 && _M_IX86 >= 300
#define _CRTAPI1 __cdecl
#else
#define _CRTAPI1
#endif
#endif


#ifndef _SIZE_T_DEFINED
typedef unsigned int size_t;
#define _SIZE_T_DEFINED
#endif


#ifndef _MAC
#ifndef _WCHAR_T_DEFINED
typedef unsigned short wchar_t;
#define _WCHAR_T_DEFINED
#endif


#ifndef _WCTYPE_T_DEFINED
typedef wchar_t wint_t;
typedef wchar_t wctype_t;
#define _WCTYPE_T_DEFINED
#endif
#endif /* ndef _MAC */


#ifndef _VA_LIST_DEFINED
#ifdef  _M_ALPHA
typedef struct {
        char *a0;       /* pointer to first homed integer argument */
        int offset;     /* byte offset of next parameter */
} va_list;
#else
typedef char *  va_list;
#endif
#define _VA_LIST_DEFINED
#endif


/* Buffered I/O macros */

#if     defined(_M_MPPC)
#define BUFSIZ  4096
#else  /* defined (_M_MPPC) */
#define BUFSIZ  512
#endif /* defined (_M_MPPC) */


/*
 * Default number of supported streams. _NFILE is confusing and obsolete, but
 * supported anyway for backwards compatibility.
 */
#define _NFILE      _NSTREAM_

#ifdef  _WIN32

#define _NSTREAM_   512

/*
 * Number of entries in _iob[] (declared below). Note that _NSTREAM_ must be
 * greater than or equal to _IOB_ENTRIES.
 */
#define _IOB_ENTRIES 20

#else   /* ndef _WIN32 */

#ifdef  _DLL
#define _NSTREAM_   128
#else
#ifdef  _MT
#define _NSTREAM_   40
#else
#define _NSTREAM_   20
#endif
#endif  /* _DLL */

#endif  /* ndef _MAC */

#define EOF     (-1)


#ifndef _FILE_DEFINED
struct _iobuf {
        char *_ptr;
        int   _cnt;
        char *_base;
        int   _flag;
        int   _file;
        int   _charbuf;
        int   _bufsiz;
        char *_tmpfname;
        };
typedef struct _iobuf FILE;
#define _FILE_DEFINED
#endif


#ifndef _MAC

/* Directory where temporary files may be created. */

#ifdef  _POSIX_
#define _P_tmpdir   "/"
#define _wP_tmpdir  L"/"
#else
#define _P_tmpdir   "\\"
#define _wP_tmpdir  L"\\"
#endif

/* L_tmpnam = size of P_tmpdir
 *            + 1 (in case P_tmpdir does not end in "/")
 *            + 12 (for the filename string)
 *            + 1 (for the null terminator)
 */
#define L_tmpnam sizeof(_P_tmpdir)+12

#else   /* def _MAC */

#define L_tmpnam 255

#endif  /* _MAC */


#ifdef  _POSIX_
#define L_ctermid   9
#define L_cuserid   32
#endif


/* Seek method constants */

#define SEEK_CUR    1
#define SEEK_END    2
#define SEEK_SET    0


#define FILENAME_MAX    260
#define FOPEN_MAX       20
#define _SYS_OPEN       20
#define TMP_MAX         32767


/* Define NULL pointer value */

#ifndef NULL
#ifdef  __cplusplus
#define NULL    0
#else
#define NULL    ((void *)0)
#endif
#endif


/* Declare _iob[] array */

#ifndef _STDIO_DEFINED
_CRTIMP extern FILE _iob[];
#endif  /* _STDIO_DEFINED */


/* Define file position type */

#ifndef _FPOS_T_DEFINED
#undef _FPOSOFF

#if defined (_POSIX_)
typedef long fpos_t;
#else /* _POSIX_ */

#if     !__STDC__ && _INTEGRAL_MAX_BITS >= 64
typedef __int64 fpos_t;
#define _FPOSOFF(fp) ((long)(fp))
#else
typedef struct fpos_t {
        unsigned int lopart;
        int          hipart;
        } fpos_t;
#define _FPOSOFF(fp) ((long)(fp).lopart)
#endif
#endif  /* _POSIX_ */

#define _FPOS_T_DEFINED
#endif


#define stdin  (&_iob[0])
#define stdout (&_iob[1])
#define stderr (&_iob[2])


#define _IOREAD         0x0001
#define _IOWRT          0x0002

#define _IOFBF          0x0000
#define _IOLBF          0x0040
#define _IONBF          0x0004

#define _IOMYBUF        0x0008
#define _IOEOF          0x0010
#define _IOERR          0x0020
#define _IOSTRG         0x0040
#define _IORW           0x0080
#ifdef _POSIX_
#define _IOAPPEND       0x0200
#endif


/* Function prototypes */

#ifndef _STDIO_DEFINED

_CRTIMP int __cdecl _filbuf(FILE *);
_CRTIMP int __cdecl _flsbuf(int, FILE *);

#ifdef  _POSIX_
_CRTIMP FILE * __cdecl _fsopen(const char *, const char *);
#else
_CRTIMP FILE * __cdecl _fsopen(const char *, const char *, int);
#endif

_CRTIMP void __cdecl clearerr(FILE *);
_CRTIMP int __cdecl fclose(FILE *);
_CRTIMP int __cdecl _fcloseall(void);

#ifdef  _POSIX_
_CRTIMP FILE * __cdecl fdopen(int, const char *);
#else
_CRTIMP FILE * __cdecl _fdopen(int, const char *);
#endif

_CRTIMP int __cdecl feof(FILE *);
_CRTIMP int __cdecl ferror(FILE *);
_CRTIMP int __cdecl fflush(FILE *);
_CRTIMP int __cdecl fgetc(FILE *);
_CRTIMP int __cdecl _fgetchar(void);
_CRTIMP int __cdecl fgetpos(FILE *, fpos_t *);
_CRTIMP char * __cdecl fgets(char *, int, FILE *);

#ifdef  _POSIX_
_CRTIMP int __cdecl fileno(FILE *);
#else
_CRTIMP int __cdecl _fileno(FILE *);
#endif

_CRTIMP int __cdecl _flushall(void);
_CRTIMP FILE * __cdecl fopen(const char *, const char *);
_CRTIMP int __cdecl fprintf(FILE *, const char *, ...);
_CRTIMP int __cdecl fputc(int, FILE *);
_CRTIMP int __cdecl _fputchar(int);
_CRTIMP int __cdecl fputs(const char *, FILE *);
_CRTIMP size_t __cdecl fread(void *, size_t, size_t, FILE *);
_CRTIMP FILE * __cdecl freopen(const char *, const char *, FILE *);
_CRTIMP int __cdecl fscanf(FILE *, const char *, ...);
_CRTIMP int __cdecl fsetpos(FILE *, const fpos_t *);
_CRTIMP int __cdecl fseek(FILE *, long, int);
_CRTIMP long __cdecl ftell(FILE *);
_CRTIMP size_t __cdecl fwrite(const void *, size_t, size_t, FILE *);
_CRTIMP int __cdecl getc(FILE *);
_CRTIMP int __cdecl getchar(void);
_CRTIMP int __cdecl _getmaxstdio(void);
_CRTIMP char * __cdecl gets(char *);
_CRTIMP int __cdecl _getw(FILE *);
_CRTIMP void __cdecl perror(const char *);
_CRTIMP int __cdecl _pclose(FILE *);
_CRTIMP FILE * __cdecl _popen(const char *, const char *);
_CRTIMP int __cdecl printf(const char *, ...);
_CRTIMP int __cdecl putc(int, FILE *);
_CRTIMP int __cdecl putchar(int);
_CRTIMP int __cdecl puts(const char *);
_CRTIMP int __cdecl _putw(int, FILE *);
_CRTIMP int __cdecl remove(const char *);
_CRTIMP int __cdecl rename(const char *, const char *);
_CRTIMP void __cdecl rewind(FILE *);
_CRTIMP int __cdecl _rmtmp(void);
_CRTIMP int __cdecl scanf(const char *, ...);
_CRTIMP void __cdecl setbuf(FILE *, char *);
_CRTIMP int __cdecl _setmaxstdio(int);
_CRTIMP int __cdecl setvbuf(FILE *, char *, int, size_t);
_CRTIMP int __cdecl _snprintf(char *, size_t, const char *, ...);
_CRTIMP int __cdecl sprintf(char *, const char *, ...);
_CRTIMP int __cdecl sscanf(const char *, const char *, ...);
_CRTIMP char * __cdecl _tempnam(const char *, const char *);
_CRTIMP FILE * __cdecl tmpfile(void);
_CRTIMP char * __cdecl tmpnam(char *);
_CRTIMP int __cdecl ungetc(int, FILE *);
_CRTIMP int __cdecl _unlink(const char *);
_CRTIMP int __cdecl vfprintf(FILE *, const char *, va_list);
_CRTIMP int __cdecl vprintf(const char *, va_list);
_CRTIMP int __cdecl _vsnprintf(char *, size_t, const char *, va_list);
_CRTIMP int __cdecl vsprintf(char *, const char *, va_list);

#ifndef _MAC
#ifndef _WSTDIO_DEFINED

/* wide function prototypes, also declared in wchar.h  */

#ifndef WEOF
#define WEOF (wint_t)(0xFFFF)
#endif

#ifdef  _POSIX_
_CRTIMP FILE * __cdecl _wfsopen(const wchar_t *, const wchar_t *);
#else
_CRTIMP FILE * __cdecl _wfsopen(const wchar_t *, const wchar_t *, int);
#endif

_CRTIMP wint_t __cdecl fgetwc(FILE *);
_CRTIMP wint_t __cdecl _fgetwchar(void);
_CRTIMP wint_t __cdecl fputwc(wint_t, FILE *);
_CRTIMP wint_t __cdecl _fputwchar(wint_t);
_CRTIMP wint_t __cdecl getwc(FILE *);
_CRTIMP wint_t __cdecl getwchar(void);
_CRTIMP wint_t __cdecl putwc(wint_t, FILE *);
_CRTIMP wint_t __cdecl putwchar(wint_t);
_CRTIMP wint_t __cdecl ungetwc(wint_t, FILE *);

_CRTIMP wchar_t * __cdecl fgetws(wchar_t *, int, FILE *);
_CRTIMP int __cdecl fputws(const wchar_t *, FILE *);
_CRTIMP wchar_t * __cdecl _getws(wchar_t *);
_CRTIMP int __cdecl _putws(const wchar_t *);

_CRTIMP int __cdecl fwprintf(FILE *, const wchar_t *, ...);
_CRTIMP int __cdecl wprintf(const wchar_t *, ...);
_CRTIMP int __cdecl _snwprintf(wchar_t *, size_t, const wchar_t *, ...);
_CRTIMP int __cdecl swprintf(wchar_t *, const wchar_t *, ...);
_CRTIMP int __cdecl vfwprintf(FILE *, const wchar_t *, va_list);
_CRTIMP int __cdecl vwprintf(const wchar_t *, va_list);
_CRTIMP int __cdecl _vsnwprintf(wchar_t *, size_t, const wchar_t *, va_list);
_CRTIMP int __cdecl vswprintf(wchar_t *, const wchar_t *, va_list);
_CRTIMP int __cdecl fwscanf(FILE *, const wchar_t *, ...);
_CRTIMP int __cdecl swscanf(const wchar_t *, const wchar_t *, ...);
_CRTIMP int __cdecl wscanf(const wchar_t *, ...);

#define getwchar()              fgetwc(stdin)
#define putwchar(_c)            fputwc((_c),stdout)
#define getwc(_stm)             fgetwc(_stm)
#define putwc(_c,_stm)          fputwc(_c,_stm)

_CRTIMP FILE * __cdecl _wfdopen(int, const wchar_t *);
_CRTIMP FILE * __cdecl _wfopen(const wchar_t *, const wchar_t *);
_CRTIMP FILE * __cdecl _wfreopen(const wchar_t *, const wchar_t *, FILE *);
_CRTIMP void __cdecl _wperror(const wchar_t *);
_CRTIMP FILE * __cdecl _wpopen(const wchar_t *, const wchar_t *);
_CRTIMP int __cdecl _wremove(const wchar_t *);
_CRTIMP wchar_t * __cdecl _wtempnam(const wchar_t *, const wchar_t *);
_CRTIMP wchar_t * __cdecl _wtmpnam(wchar_t *);


#define _WSTDIO_DEFINED
#endif  /* _WSTDIO_DEFINED */
#endif /* ndef _MAC */

#define _STDIO_DEFINED
#endif  /* _STDIO_DEFINED */


/* Macro definitions */

#define feof(_stream)     ((_stream)->_flag & _IOEOF)
#define ferror(_stream)   ((_stream)->_flag & _IOERR)
#define _fileno(_stream)  ((_stream)->_file)
#define getc(_stream)     (--(_stream)->_cnt >= 0 \
                ? 0xff & *(_stream)->_ptr++ : _filbuf(_stream))
#define putc(_c,_stream)  (--(_stream)->_cnt >= 0 \
                ? 0xff & (*(_stream)->_ptr++ = (char)(_c)) :  _flsbuf((_c),(_stream)))
#define getchar()         getc(stdin)
#define putchar(_c)       putc((_c),stdout)



#ifdef  _MT
#undef  getc
#undef  putc
#undef  getchar
#undef  putchar
#endif



#if     !__STDC__ && !defined(_POSIX_)

/* Non-ANSI names for compatibility */

#define P_tmpdir  _P_tmpdir
#define SYS_OPEN  _SYS_OPEN

_CRTIMP int __cdecl fcloseall(void);
_CRTIMP FILE * __cdecl fdopen(int, const char *);
_CRTIMP int __cdecl fgetchar(void);
_CRTIMP int __cdecl fileno(FILE *);
_CRTIMP int __cdecl flushall(void);
_CRTIMP int __cdecl fputchar(int);
_CRTIMP int __cdecl getw(FILE *);
_CRTIMP int __cdecl putw(int, FILE *);
_CRTIMP int __cdecl rmtmp(void);
_CRTIMP char * __cdecl tempnam(const char *, const char *);
_CRTIMP int __cdecl unlink(const char *);

#endif  /* __STDC__ */

#ifdef  __cplusplus
}
#endif

#ifdef  _MSC_VER
#pragma pack(pop)
#endif  /* _MSC_VER */

#endif  /* _INC_STDIO */







                                                               

非常长
   

看看就算了，没必要看懂它。除非是自己写的头文件。

  没看懂，能学么？

不用学它的，你要学的是自己写的，将来你需要编写大量类似的东西，但没必要跟它一样。那里很多设置是编译器依据自己版本专用的动作，跟你没太大关系，看懂了也没用。看一看，只是知道编译器对我们所写的源代码，其实动了手脚，很多自己以为写得很漂亮的代码，其实还是跟原来一样。比如很多人以为?:的效率很高，写在一行上，但其实在编译器编译时，这种代码被改回了if else格式，这些改动，就是在这些头文件中做的。再如printf()，你在这个头文件中能找到，它编译时实际上就不是printf()，而是根据版本和选项设置的不同被改成了另外的函数名，而这种函数名是有些人刻意回避的。

抽象啊

    嗯，我知道像printf()这些函数，是软件自己就给编好了，但是如果我想自己写个函数，然后创个自己的头文件包含起来，以后用这个函数就直接调用，不用再写上一堆代码了。

我原来也有这样的疑问，不过后来看书讲头文件就是要用来隐藏implement的复杂性的，所以也就不追究了

头文件是作全局变量声明、函数原型、宏定义、常量声明之类用的，不是写代码用的。

其实你平时写程序都有以下的东西，比如：
#define PI    3.1415926
int max(int i, int j);

把上面的两行，搬到一个叫my.h的头文件中，然后，在原先的.c文件原来的位置，写
#include "my.h"

这样，就是头文件的用法了。

但是，不要以为原先
int max(int i, int j)
{
}
这里的函数体可以搬到my.h去，正确的写法是把这部分代码另外储存为一个.c文件，比如max.c。

这样，原先的程序，就只有#include和main()函数代码，干净多了。头文件就是这种用场。

stdio.h中的printf()函数，只是原型声明，没有函数代码，那些代码没人看到过，恐怕除了原先那个作者，没人知道它是怎么写的。

我一直有个疑问啊：
我看书里面也是说头文件只供函数说明用，是implement和user的接口。具体的implement是在另外一个.c或.cpp文件里面的。
可是我写程序的时候，比如#include<a.h>   编译程序如何去找到那个a.cpp呢？
一直以来我都是在自己的*.h中加入一句#include<*.cpp>,来让编译程序找到.cpp的
我就想不通如何写出没有函数代码的h文件？