Question

我想知道是否有任何可能的方法来编写C/C++程序而不使用头文件。

#include <iostream.h> //I want this same code to work without including this line
#include <conio.h>    //I want this same code to work without including this line

int main ()
{
  clrscr();
  char str [80];
  int num;
  cout<<"Enter the string : "<<str;
  cin>>str;
  cout<<"Enter the number : "<<num;
  cin>>num;
  getch();  
  return 0;
}

我了解到C我们可以在不使用stdio.h的情况下使用scanf()函数

示例：

#include <stdio.h>

int main ()
{
  char str [80];
  scanf ("%s",str);  
  return 0;
}

以上代码可以写成

extern int scanf(const char *format, ...);

int main ()
{
  char str [80];
  scanf ("%s",str);  
  return 0;
}

通过致电extern int scanf(const char *format, ...);，scanf()将无缝运作。

我是一名培训师，我的学生问我这个奇怪的疑问及其原因。我需要了解如何使用某些代码实现，就像extern int scanf(const char *format, ...);替换stdio.h

一样

Answer 1

我不确定我理解你的问题背后的原因，但有一种（非常难看）的方式。

只需使用预处理器（而不是编译器）和正确的选项（取决于您的环境），它将生成一个可以编译的无标题的等效CPP文件。

手动做同样的事情很容易出错......在我看来完全没用。

以下是基于问题中提供的代码的示例。

#include <stdio.h>

int main ()
{
    char str [80];
      scanf ("%s",str);
        return 0;
}

使用命令gcc -E main.cpp|grep -v "^#" |grep -v "^$"我提取了以下代码（请注意，我的grep命令删除了以＃和空行开头的行）：

extern "C" {
typedef unsigned int size_t;
typedef unsigned char __u_char;
typedef unsigned short int __u_short;
typedef unsigned int __u_int;
typedef unsigned long int __u_long;
typedef signed char __int8_t;
typedef unsigned char __uint8_t;
typedef signed short int __int16_t;
typedef unsigned short int __uint16_t;
typedef signed int __int32_t;
typedef unsigned int __uint32_t;
__extension__ typedef signed long long int __int64_t;
__extension__ typedef unsigned long long int __uint64_t;
__extension__ typedef long long int __quad_t;
__extension__ typedef unsigned long long int __u_quad_t;
__extension__ typedef __u_quad_t __dev_t;
__extension__ typedef unsigned int __uid_t;
__extension__ typedef unsigned int __gid_t;
__extension__ typedef unsigned long int __ino_t;
__extension__ typedef __u_quad_t __ino64_t;
__extension__ typedef unsigned int __mode_t;
__extension__ typedef unsigned int __nlink_t;
__extension__ typedef long int __off_t;
__extension__ typedef __quad_t __off64_t;
__extension__ typedef int __pid_t;
__extension__ typedef struct { int __val[2]; } __fsid_t;
__extension__ typedef long int __clock_t;
__extension__ typedef unsigned long int __rlim_t;
__extension__ typedef __u_quad_t __rlim64_t;
__extension__ typedef unsigned int __id_t;
__extension__ typedef long int __time_t;
__extension__ typedef unsigned int __useconds_t;
__extension__ typedef long int __suseconds_t;
__extension__ typedef int __daddr_t;
__extension__ typedef long int __swblk_t;
__extension__ typedef int __key_t;
__extension__ typedef int __clockid_t;
__extension__ typedef void * __timer_t;
__extension__ typedef long int __blksize_t;
__extension__ typedef long int __blkcnt_t;
__extension__ typedef __quad_t __blkcnt64_t;
__extension__ typedef unsigned long int __fsblkcnt_t;
__extension__ typedef __u_quad_t __fsblkcnt64_t;
__extension__ typedef unsigned long int __fsfilcnt_t;
__extension__ typedef __u_quad_t __fsfilcnt64_t;
__extension__ typedef int __ssize_t;
typedef __off64_t __loff_t;
typedef __quad_t *__qaddr_t;
typedef char *__caddr_t;
__extension__ typedef int __intptr_t;
__extension__ typedef unsigned int __socklen_t;
struct _IO_FILE;
typedef struct _IO_FILE FILE;
typedef struct _IO_FILE __FILE;
typedef struct
{
  int __count;
  union
  {
    unsigned int __wch;
    char __wchb[4];
  } __value;
} __mbstate_t;
typedef struct
{
  __off_t __pos;
  __mbstate_t __state;
} _G_fpos_t;
typedef struct
{
  __off64_t __pos;
  __mbstate_t __state;
} _G_fpos64_t;
typedef int _G_int16_t __attribute__ ((__mode__ (__HI__)));
typedef int _G_int32_t __attribute__ ((__mode__ (__SI__)));
typedef unsigned int _G_uint16_t __attribute__ ((__mode__ (__HI__)));
typedef unsigned int _G_uint32_t __attribute__ ((__mode__ (__SI__)));
typedef __builtin_va_list __gnuc_va_list;
struct _IO_jump_t; struct _IO_FILE;
typedef void _IO_lock_t;
struct _IO_marker {
  struct _IO_marker *_next;
  struct _IO_FILE *_sbuf;
  int _pos;
};
enum __codecvt_result
{
  __codecvt_ok,
  __codecvt_partial,
  __codecvt_error,
  __codecvt_noconv
};
struct _IO_FILE {
  int _flags;
  char* _IO_read_ptr;
  char* _IO_read_end;
  char* _IO_read_base;
  char* _IO_write_base;
  char* _IO_write_ptr;
  char* _IO_write_end;
  char* _IO_buf_base;
  char* _IO_buf_end;
  char *_IO_save_base;
  char *_IO_backup_base;
  char *_IO_save_end;
  struct _IO_marker *_markers;
  struct _IO_FILE *_chain;
  int _fileno;
  int _flags2;
  __off_t _old_offset;
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];
  _IO_lock_t *_lock;
  __off64_t _offset;
  void *__pad1;
  void *__pad2;
  void *__pad3;
  void *__pad4;
  size_t __pad5;
  int _mode;
  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
};
struct _IO_FILE_plus;
extern struct _IO_FILE_plus _IO_2_1_stdin_;
extern struct _IO_FILE_plus _IO_2_1_stdout_;
extern struct _IO_FILE_plus _IO_2_1_stderr_;
typedef __ssize_t __io_read_fn (void *__cookie, char *__buf, size_t __nbytes);
typedef __ssize_t __io_write_fn (void *__cookie, __const char *__buf,
     size_t __n);
typedef int __io_seek_fn (void *__cookie, __off64_t *__pos, int __w);
typedef int __io_close_fn (void *__cookie);
typedef __io_read_fn cookie_read_function_t;
typedef __io_write_fn cookie_write_function_t;
typedef __io_seek_fn cookie_seek_function_t;
typedef __io_close_fn cookie_close_function_t;
typedef struct
{
  __io_read_fn *read;
  __io_write_fn *write;
  __io_seek_fn *seek;
  __io_close_fn *close;
} _IO_cookie_io_functions_t;
typedef _IO_cookie_io_functions_t cookie_io_functions_t;
struct _IO_cookie_file;
extern void _IO_cookie_init (struct _IO_cookie_file *__cfile, int __read_write,
        void *__cookie, _IO_cookie_io_functions_t __fns);
extern "C" {
extern int __underflow (_IO_FILE *);
extern int __uflow (_IO_FILE *);
extern int __overflow (_IO_FILE *, int);
extern int _IO_getc (_IO_FILE *__fp);
extern int _IO_putc (int __c, _IO_FILE *__fp);
extern int _IO_feof (_IO_FILE *__fp) throw ();
extern int _IO_ferror (_IO_FILE *__fp) throw ();
extern int _IO_peekc_locked (_IO_FILE *__fp);
extern void _IO_flockfile (_IO_FILE *) throw ();
extern void _IO_funlockfile (_IO_FILE *) throw ();
extern int _IO_ftrylockfile (_IO_FILE *) throw ();
extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict,
   __gnuc_va_list, int *__restrict);
extern int _IO_vfprintf (_IO_FILE *__restrict, const char *__restrict,
    __gnuc_va_list);
extern __ssize_t _IO_padn (_IO_FILE *, int, __ssize_t);
extern size_t _IO_sgetn (_IO_FILE *, void *, size_t);
extern __off64_t _IO_seekoff (_IO_FILE *, __off64_t, int, int);
extern __off64_t _IO_seekpos (_IO_FILE *, __off64_t, int);
extern void _IO_free_backup_area (_IO_FILE *) throw ();
}
typedef __gnuc_va_list va_list;
typedef __off_t off_t;
typedef __off64_t off64_t;
typedef __ssize_t ssize_t;
typedef _G_fpos_t fpos_t;
typedef _G_fpos64_t fpos64_t;
extern struct _IO_FILE *stdin;
extern struct _IO_FILE *stdout;
extern struct _IO_FILE *stderr;
extern int remove (__const char *__filename) throw ();
extern int rename (__const char *__old, __const char *__new) throw ();
extern int renameat (int __oldfd, __const char *__old, int __newfd,
       __const char *__new) throw ();
extern FILE *tmpfile (void) ;
extern FILE *tmpfile64 (void) ;
extern char *tmpnam (char *__s) throw () ;
extern char *tmpnam_r (char *__s) throw () ;
extern char *tempnam (__const char *__dir, __const char *__pfx)
     throw () __attribute__ ((__malloc__)) ;
extern int fclose (FILE *__stream);
extern int fflush (FILE *__stream);
extern int fflush_unlocked (FILE *__stream);
extern int fcloseall (void);
extern FILE *fopen (__const char *__restrict __filename,
      __const char *__restrict __modes) ;
extern FILE *freopen (__const char *__restrict __filename,
        __const char *__restrict __modes,
        FILE *__restrict __stream) ;
extern FILE *fopen64 (__const char *__restrict __filename,
        __const char *__restrict __modes) ;
extern FILE *freopen64 (__const char *__restrict __filename,
   __const char *__restrict __modes,
   FILE *__restrict __stream) ;
extern FILE *fdopen (int __fd, __const char *__modes) throw () ;
extern FILE *fopencookie (void *__restrict __magic_cookie,
     __const char *__restrict __modes,
     _IO_cookie_io_functions_t __io_funcs) throw () ;
extern FILE *fmemopen (void *__s, size_t __len, __const char *__modes)
  throw () ;
extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) throw () ;
extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) throw ();
extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,
      int __modes, size_t __n) throw ();
extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,
         size_t __size) throw ();
extern void setlinebuf (FILE *__stream) throw ();
extern int fprintf (FILE *__restrict __stream,
      __const char *__restrict __format, ...);
extern int printf (__const char *__restrict __format, ...);
extern int sprintf (char *__restrict __s,
      __const char *__restrict __format, ...) throw ();
extern int vfprintf (FILE *__restrict __s, __const char *__restrict __format,
       __gnuc_va_list __arg);
extern int vprintf (__const char *__restrict __format, __gnuc_va_list __arg);
extern int vsprintf (char *__restrict __s, __const char *__restrict __format,
       __gnuc_va_list __arg) throw ();
extern int snprintf (char *__restrict __s, size_t __maxlen,
       __const char *__restrict __format, ...)
     throw () __attribute__ ((__format__ (__printf__, 3, 4)));
extern int vsnprintf (char *__restrict __s, size_t __maxlen,
        __const char *__restrict __format, __gnuc_va_list __arg)
     throw () __attribute__ ((__format__ (__printf__, 3, 0)));
extern int vasprintf (char **__restrict __ptr, __const char *__restrict __f,
        __gnuc_va_list __arg)
     throw () __attribute__ ((__format__ (__printf__, 2, 0))) ;
extern int __asprintf (char **__restrict __ptr,
         __const char *__restrict __fmt, ...)
     throw () __attribute__ ((__format__ (__printf__, 2, 3))) ;
extern int asprintf (char **__restrict __ptr,
       __const char *__restrict __fmt, ...)
     throw () __attribute__ ((__format__ (__printf__, 2, 3))) ;
extern int vdprintf (int __fd, __const char *__restrict __fmt,
       __gnuc_va_list __arg)
     __attribute__ ((__format__ (__printf__, 2, 0)));
extern int dprintf (int __fd, __const char *__restrict __fmt, ...)
     __attribute__ ((__format__ (__printf__, 2, 3)));
extern int fscanf (FILE *__restrict __stream,
     __const char *__restrict __format, ...) ;
extern int scanf (__const char *__restrict __format, ...) ;
extern int sscanf (__const char *__restrict __s,
     __const char *__restrict __format, ...) throw ();
extern int vfscanf (FILE *__restrict __s, __const char *__restrict __format,
      __gnuc_va_list __arg)
     __attribute__ ((__format__ (__scanf__, 2, 0))) ;
extern int vscanf (__const char *__restrict __format, __gnuc_va_list __arg)
     __attribute__ ((__format__ (__scanf__, 1, 0))) ;
extern int vsscanf (__const char *__restrict __s,
      __const char *__restrict __format, __gnuc_va_list __arg)
     throw () __attribute__ ((__format__ (__scanf__, 2, 0)));
extern int fgetc (FILE *__stream);
extern int getc (FILE *__stream);
extern int getchar (void);
extern int getc_unlocked (FILE *__stream);
extern int getchar_unlocked (void);
extern int fgetc_unlocked (FILE *__stream);
extern int fputc (int __c, FILE *__stream);
extern int putc (int __c, FILE *__stream);
extern int putchar (int __c);
extern int fputc_unlocked (int __c, FILE *__stream);
extern int putc_unlocked (int __c, FILE *__stream);
extern int putchar_unlocked (int __c);
extern int getw (FILE *__stream);
extern int putw (int __w, FILE *__stream);
extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
     ;
extern char *gets (char *__s) ;
extern char *fgets_unlocked (char *__restrict __s, int __n,
        FILE *__restrict __stream) ;
extern __ssize_t __getdelim (char **__restrict __lineptr,
          size_t *__restrict __n, int __delimiter,
          FILE *__restrict __stream) ;
extern __ssize_t getdelim (char **__restrict __lineptr,
        size_t *__restrict __n, int __delimiter,
        FILE *__restrict __stream) ;
extern __ssize_t getline (char **__restrict __lineptr,
       size_t *__restrict __n,
       FILE *__restrict __stream) ;
extern int fputs (__const char *__restrict __s, FILE *__restrict __stream);
extern int puts (__const char *__s);
extern int ungetc (int __c, FILE *__stream);
extern size_t fread (void *__restrict __ptr, size_t __size,
       size_t __n, FILE *__restrict __stream) ;
extern size_t fwrite (__const void *__restrict __ptr, size_t __size,
        size_t __n, FILE *__restrict __s);
extern int fputs_unlocked (__const char *__restrict __s,
      FILE *__restrict __stream);
extern size_t fread_unlocked (void *__restrict __ptr, size_t __size,
         size_t __n, FILE *__restrict __stream) ;
extern size_t fwrite_unlocked (__const void *__restrict __ptr, size_t __size,
          size_t __n, FILE *__restrict __stream);
extern int fseek (FILE *__stream, long int __off, int __whence);
extern long int ftell (FILE *__stream) ;
extern void rewind (FILE *__stream);
extern int fseeko (FILE *__stream, __off_t __off, int __whence);
extern __off_t ftello (FILE *__stream) ;
extern int fgetpos (FILE *__restrict __stream, fpos_t *__restrict __pos);
extern int fsetpos (FILE *__stream, __const fpos_t *__pos);
extern int fseeko64 (FILE *__stream, __off64_t __off, int __whence);
extern __off64_t ftello64 (FILE *__stream) ;
extern int fgetpos64 (FILE *__restrict __stream, fpos64_t *__restrict __pos);
extern int fsetpos64 (FILE *__stream, __const fpos64_t *__pos);
extern void clearerr (FILE *__stream) throw ();
extern int feof (FILE *__stream) throw () ;
extern int ferror (FILE *__stream) throw () ;
extern void clearerr_unlocked (FILE *__stream) throw ();
extern int feof_unlocked (FILE *__stream) throw () ;
extern int ferror_unlocked (FILE *__stream) throw () ;
extern void perror (__const char *__s);
extern int sys_nerr;
extern __const char *__const sys_errlist[];
extern int _sys_nerr;
extern __const char *__const _sys_errlist[];
extern int fileno (FILE *__stream) throw () ;
extern int fileno_unlocked (FILE *__stream) throw () ;
extern FILE *popen (__const char *__command, __const char *__modes) ;
extern int pclose (FILE *__stream);
extern char *ctermid (char *__s) throw ();
extern char *cuserid (char *__s);
struct obstack;
extern int obstack_printf (struct obstack *__restrict __obstack,
      __const char *__restrict __format, ...)
     throw () __attribute__ ((__format__ (__printf__, 2, 3)));
extern int obstack_vprintf (struct obstack *__restrict __obstack,
       __const char *__restrict __format,
       __gnuc_va_list __args)
     throw () __attribute__ ((__format__ (__printf__, 2, 0)));
extern void flockfile (FILE *__stream) throw ();
extern int ftrylockfile (FILE *__stream) throw () ;
extern void funlockfile (FILE *__stream) throw ();
}
int main ()
{
    char str [80];
      scanf ("%s",str);
        return 0;
}

是的，它确实伤了眼睛......

Answer 2

是。请记住，#include读取文件并将其放在此编译器指令的位置。因此，您只需手动将stdio.h和其他标题的内容复制到cpp文件中，然后将代码附加到底部。

不建议使用;）

编辑：回复评论：

在这里：http://pastebin.com/QG7MM3a7

Answer 3

C11标准，§7.1.4/ 2保证：

如果可以声明库函数而不引用标头中定义的任何类型，则允许声明该函数并使用它而不包括其关联的标题。

因此，您的程序对任何宣称自己与C编程语言兼容的内容都是有效的输入。

确实，任何此类系统都保证在printf内声明stdio.h，因此使用#include会更容易（也更明显）。

但是包含标题也有可能不合需要的副作用：在C中，它会导致标题声明的标识符被保留为宏名称。（因此，如果您不包含#define printf foo，则只能<stdio.h> 。）在C ++中，包括任何标准标头会导致所有标识符都是关键字，或者在任何标准中定义标题，成为宏名称保留。（在C中，我在标准中找不到像#define while 42那样禁止你的东西，但可能有相当的东西。）

所以，如果你想让权限重新定义关键字到其他东西，请随意编写程序。但是，除了可能非常关心合规性的编译器作者之外，没有人会愿意帮助你，但我们更倾向于以精确的法律术语来表达投诉。如果没有这样做，你的情况就会变得没有人会帮助或与你合作。

Answer 4

简答：是的

答案很长：是的，但你可能不会获得太多收益，因为你最终会自己复制大部分工作。

头文件，如stdio.h，通常提供许多函数声明。请注意，声明不是定义。声明只告诉编译器相信该函数存在（并允许您调用它），而定义提供函数本身的代码。

您正在为scanf（）提供声明，因此编译器允许您调用它。但是，stdio.h头文件已经为scanf提供了一个声明，所以你并没有真正获得很多东西。此外，这个正常工作的唯一原因是因为scanf（）的定义恰好存在于您的可执行文件中 - 很可能是因为它是一个库函数，并且您的编译器自动包含该库。如果它没有包含包含scanf（）的库，则链接器（在编译器之后运行）会抱怨，并且在“未定义引用scanf（）...”的行中给出错误。

因此，您可以通过为要使用的所有库函数提供声明来避免使用标准标题，但是您必须小心，您提供的声明与库中包含的声明完全匹配（否则您可能从链接器获取未解决的符号/引用错误）。这实际上是大多数标题的工作 - 它们充当不同代码模块之间的“契约”。在这种情况下，stdio.h头是标准库提供的一些函数的“契约”：它允许您通过提供声明来调用它们，但此外，它隐含地声称这些函数的定义存在于某处。

考虑到所有这些，您是否真的想避免包含标题并且必须手动选择和声明您声明的功能（同时进行交叉检查以确保您的声明正确）？

编辑：我可能误解了问题的目的。是的，您应该能够编写几乎所有程序并使用几乎所有API而不实际包含标题，但您必须繁琐地交叉检查所有声明以确保它们是正确的。您还将失去标头提供的任何内联定义以进行优化。

没有头文件的C / C ++程序

4 个答案: