5

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scanf()不使用 stdio.h 的情况下使用函数

例子：

#include <stdio.h>

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

上面的代码可以写成

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

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

在这里通过调用extern int scanf(const char *format, ...);，scanf()将无缝工作。

我是一名培训师，我的学生问我这个奇怪的疑问及其原因。我需要如何用一些代码来实现它，就像extern int scanf(const char *format, ...);替换一样stdio.h

4

4 回答 4

8

我不确定我是否理解您的问题背后的原因，但有一种（非常丑陋的）方式。

只需使用带有正确选项（取决于您的环境）的预处理器（而不是编译器），它将生成一个可以编译的无头等效 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;
}

使用该命令，gcc -E main.cpp|grep -v "^#" |grep -v "^$"我提取了以下代码（请注意，以 # 开头的行和空行已被我的 grep 命令删除）：

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，它确实有点伤眼睛......

于 2013-08-14T05:34:15.913 回答
4

是的。请记住，它#include会读取文件并将其按字面意思放在此编译器指令的位置。因此，您可以简单地手动将内容stdio.h和其他标头复制到您的cpp文件中，并将您的代码附加到底部。

不过不推荐；）

编辑：回应评论：

给你： http: //pastebin.com/QG7MM3a7

于 2013-08-14T05:57:02.507 回答
3

C11 标准，§7.1.4/2 保证：

如果可以在不引用头文件中定义的任何类型的情况下声明库函数，则也允许声明函数并在不包括其关联头文件的情况下使用它。

因此，您的程序是任何标榜自己与 C 编程语言兼容的任何东西的有效输入。

确实，任何这样的系统也保证在printfinside声明stdio.h，因此使用起来会更容易（也更明显）#include。

但是包含头文件也有可能不受欢迎的副作用：在 C 中，它会导致头文件声明的标识符被保留为宏名称。（因此，#define printf foo 只有在不包含时才能这样做<stdio.h>。）在 C++ 中，包含任何标准头文件会导致所有作为关键字或在任何标准头文件中定义的标识符都保留为宏名称。（在 C 语言中，我无法在标准中找到禁止您使用类似 的内容#define while 42，但可能有等价的内容。）

所以，如果你想要疯狂地重新定义其他事物的关键字，请随意以这种方式编写程序。但是，除了非常关心合规性的编译器作者之外，没有人愿意帮助您，但我们倾向于使用精确的法律术语来表达投诉。如果无法做到这一点，您的情况将变成没有人会帮助您或与您合作。

于 2013-08-14T05:32:42.057 回答
2

简短的回答：是的

长答案：是的，但是您可能不会获得太多收益，因为您最终会自己复制大部分工作。

头文件，如 stdio.h，通常提供大量函数声明。请注意，声明不是定义。声明只是告诉编译器相信该函数存在（并允许您调用它），而定义为函数本身提供代码。

您正在为 scanf() 提供声明，因此编译器允许您调用它。然而，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。此外，这样做的唯一原因是因为 scanf() 的定义恰好已经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）会抱怨并给你一个错误，类似于“对 scanf() 的未定义引用 ...”。

因此，您可以通过为您希望使用的所有库函数提供声明来避免使用标准头文件，但您必须注意您提供的声明与库中包含的内容完全匹配（否则您可能会得到未解析的符号/来自链接器的引用错误）。这实际上是大多数标头的工作——它们充当不同代码模块之间的“合同”。在这种情况下，stdio.h 头文件是标准库提供的某些函数的“合同”：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不得不手动选择要声明的函数（同时进行交叉检查以确保声明正确）？

编辑：我可能误解了这个问题的目的。是的，您应该能够编写几乎任何程序并使用几乎所有 API，而无需实际包含标头，但是您必须繁琐地交叉检查所有声明以确保它们是正确的。您还将失去标题提供的用于优化的任何内联定义。

于 2013-08-14T05:34:52.250 回答