Note:gcc -E hello.c -o hello.i生成的hello.i中的__extension__什么意思

gcc预编译会去掉源码中所有的注释,并展开所有#<include *>选项

但其中会出现不少__extension__,这个__extension__是什么意思呢?

简单的说,gcc对ANSI C标准进行了扩展,使用这些扩展时,编译器会抛出警告。使用__extension__关键字告诉gcc不要抛出警告!

 

gcc -E hello.c -o hello.i生成的hello.i过程及源码如下:

注:hello.i是被部分修改过的,为了显示预编译处理的嵌套过程

hello.c

 

#include<stdio.h>

int main()
{
	printf("Hello,world\n");
	return 0;
}

使用命令预编译:

 

gcc -E hello.c -o hello.i

生成hello.i

 

# 1 "hello.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "hello.c"
# 1 "/usr/include/stdio.h" 1 3 4
# 28 "/usr/include/stdio.h" 3 4
#       1 "/usr/include/features.h" 1 3 4
#       322 "/usr/include/features.h" 3 4
#               1 "/usr/include/bits/predefs.h" 1 3 4
#       323 "/usr/include/features.h" 2 3 4
#       
#       355 "/usr/include/features.h" 3 4
#               1 "/usr/include/sys/cdefs.h" 1 3 4
#                       353 "/usr/include/sys/cdefs.h" 3 4
#                               1 "/usr/include/bits/wordsize.h" 1 3 4
#                       354 "/usr/include/sys/cdefs.h" 2 3 4
#       356 "/usr/include/features.h" 2 3 4
# 
#       387 "/usr/include/features.h" 3 4
#              1 "/usr/include/gnu/stubs.h" 1 3 4
#                       1 "/usr/include/bits/wordsize.h" 1 3 4
#               5 "/usr/include/gnu/stubs.h" 2 3 4
#                        1 "/usr/include/gnu/stubs-32.h" 1 3 4
                # 8 "/usr/include/gnu/stubs.h" 2 3 4
        # 388 "/usr/include/features.h" 2 3 4
# 29 "/usr/include/stdio.h" 2 3 4





# 1 "/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stddef.h" 1 3 4
# 211 "/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stddef.h" 3 4
typedef unsigned int size_t;
# 35 "/usr/include/stdio.h" 2 3 4

# 1 "/usr/include/bits/types.h" 1 3 4
# 28 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 29 "/usr/include/bits/types.h" 2 3 4


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;
# 131 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/typesizes.h" 1 3 4
# 132 "/usr/include/bits/types.h" 2 3 4


__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;
# 37 "/usr/include/stdio.h" 2 3 4
# 45 "/usr/include/stdio.h" 3 4
struct _IO_FILE;



typedef struct _IO_FILE FILE;





# 65 "/usr/include/stdio.h" 3 4
typedef struct _IO_FILE __FILE;
# 75 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/libio.h" 1 3 4
# 32 "/usr/include/libio.h" 3 4
# 1 "/usr/include/_G_config.h" 1 3 4
# 15 "/usr/include/_G_config.h" 3 4
# 1 "/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stddef.h" 1 3 4
# 16 "/usr/include/_G_config.h" 2 3 4




# 1 "/usr/include/wchar.h" 1 3 4
# 83 "/usr/include/wchar.h" 3 4
typedef struct
{
  int __count;
  union
  {

    unsigned int __wch;



    char __wchb[4];
  } __value;
} __mbstate_t;
# 21 "/usr/include/_G_config.h" 2 3 4

typedef struct
{
  __off_t __pos;
  __mbstate_t __state;
} _G_fpos_t;
typedef struct
{
  __off64_t __pos;
  __mbstate_t __state;
} _G_fpos64_t;
# 53 "/usr/include/_G_config.h" 3 4
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__)));
# 33 "/usr/include/libio.h" 2 3 4
# 53 "/usr/include/libio.h" 3 4
# 1 "/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stdarg.h" 1 3 4
# 40 "/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stdarg.h" 3 4
typedef __builtin_va_list __gnuc_va_list;
# 54 "/usr/include/libio.h" 2 3 4
# 170 "/usr/include/libio.h" 3 4
struct _IO_jump_t; struct _IO_FILE;
# 180 "/usr/include/libio.h" 3 4
typedef void _IO_lock_t;





struct _IO_marker {
  struct _IO_marker *_next;
  struct _IO_FILE *_sbuf;



  int _pos;
# 203 "/usr/include/libio.h" 3 4
};


enum __codecvt_result
{
  __codecvt_ok,
  __codecvt_partial,
  __codecvt_error,
  __codecvt_noconv
};
# 271 "/usr/include/libio.h" 3 4
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;
# 319 "/usr/include/libio.h" 3 4
  __off64_t _offset;
# 328 "/usr/include/libio.h" 3 4
  void *__pad1;
  void *__pad2;
  void *__pad3;
  void *__pad4;
  size_t __pad5;

  int _mode;

  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];

};


typedef struct _IO_FILE _IO_FILE;


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_;
# 364 "/usr/include/libio.h" 3 4
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);
# 416 "/usr/include/libio.h" 3 4
extern int __underflow (_IO_FILE *);
extern int __uflow (_IO_FILE *);
extern int __overflow (_IO_FILE *, int);
# 460 "/usr/include/libio.h" 3 4
extern int _IO_getc (_IO_FILE *__fp);
extern int _IO_putc (int __c, _IO_FILE *__fp);
extern int _IO_feof (_IO_FILE *__fp) __attribute__ ((__nothrow__));
extern int _IO_ferror (_IO_FILE *__fp) __attribute__ ((__nothrow__));

extern int _IO_peekc_locked (_IO_FILE *__fp);





extern void _IO_flockfile (_IO_FILE *) __attribute__ ((__nothrow__));
extern void _IO_funlockfile (_IO_FILE *) __attribute__ ((__nothrow__));
extern int _IO_ftrylockfile (_IO_FILE *) __attribute__ ((__nothrow__));
# 490 "/usr/include/libio.h" 3 4
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 *) __attribute__ ((__nothrow__));
# 76 "/usr/include/stdio.h" 2 3 4




typedef __gnuc_va_list va_list;
# 91 "/usr/include/stdio.h" 3 4
typedef __off_t off_t;
# 103 "/usr/include/stdio.h" 3 4
typedef __ssize_t ssize_t;







typedef _G_fpos_t fpos_t;




# 161 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/bits/stdio_lim.h" 1 3 4
# 162 "/usr/include/stdio.h" 2 3 4



extern struct _IO_FILE *stdin;
extern struct _IO_FILE *stdout;
extern struct _IO_FILE *stderr;







extern int remove (__const char *__filename) __attribute__ ((__nothrow__));

extern int rename (__const char *__old, __const char *__new) __attribute__ ((__nothrow__));




extern int renameat (int __oldfd, __const char *__old, int __newfd,
       __const char *__new) __attribute__ ((__nothrow__));








extern FILE *tmpfile (void) ;
# 206 "/usr/include/stdio.h" 3 4
extern char *tmpnam (char *__s) __attribute__ ((__nothrow__)) ;





extern char *tmpnam_r (char *__s) __attribute__ ((__nothrow__)) ;
# 224 "/usr/include/stdio.h" 3 4
extern char *tempnam (__const char *__dir, __const char *__pfx)
     __attribute__ ((__nothrow__)) __attribute__ ((__malloc__)) ;








extern int fclose (FILE *__stream);




extern int fflush (FILE *__stream);

# 249 "/usr/include/stdio.h" 3 4
extern int fflush_unlocked (FILE *__stream);
# 263 "/usr/include/stdio.h" 3 4






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) ;
# 292 "/usr/include/stdio.h" 3 4

# 303 "/usr/include/stdio.h" 3 4
extern FILE *fdopen (int __fd, __const char *__modes) __attribute__ ((__nothrow__)) ;
# 316 "/usr/include/stdio.h" 3 4
extern FILE *fmemopen (void *__s, size_t __len, __const char *__modes)
  __attribute__ ((__nothrow__)) ;




extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) __attribute__ ((__nothrow__)) ;






extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __attribute__ ((__nothrow__));



extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,
      int __modes, size_t __n) __attribute__ ((__nothrow__));





extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,
         size_t __size) __attribute__ ((__nothrow__));


extern void setlinebuf (FILE *__stream) __attribute__ ((__nothrow__));








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, ...) __attribute__ ((__nothrow__));





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) __attribute__ ((__nothrow__));





extern int snprintf (char *__restrict __s, size_t __maxlen,
       __const char *__restrict __format, ...)
     __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 4)));

extern int vsnprintf (char *__restrict __s, size_t __maxlen,
        __const char *__restrict __format, __gnuc_va_list __arg)
     __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 0)));

# 414 "/usr/include/stdio.h" 3 4
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, ...) __attribute__ ((__nothrow__));
# 445 "/usr/include/stdio.h" 3 4
extern int fscanf (FILE *__restrict __stream, __const char *__restrict __format, ...) __asm__ ("" "__isoc99_fscanf") ;


extern int scanf (__const char *__restrict __format, ...) __asm__ ("" "__isoc99_scanf") ;

extern int sscanf (__const char *__restrict __s, __const char *__restrict __format, ...) __asm__ ("" "__isoc99_sscanf") __attribute__ ((__nothrow__));
# 465 "/usr/include/stdio.h" 3 4








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)
     __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__scanf__, 2, 0)));
# 496 "/usr/include/stdio.h" 3 4
extern int vfscanf (FILE *__restrict __s, __const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vfscanf")



     __attribute__ ((__format__ (__scanf__, 2, 0))) ;
extern int vscanf (__const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vscanf")

     __attribute__ ((__format__ (__scanf__, 1, 0))) ;
extern int vsscanf (__const char *__restrict __s, __const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vsscanf") __attribute__ ((__nothrow__))



     __attribute__ ((__format__ (__scanf__, 2, 0)));
# 524 "/usr/include/stdio.h" 3 4









extern int fgetc (FILE *__stream);
extern int getc (FILE *__stream);





extern int getchar (void);

# 552 "/usr/include/stdio.h" 3 4
extern int getc_unlocked (FILE *__stream);
extern int getchar_unlocked (void);
# 563 "/usr/include/stdio.h" 3 4
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);

# 596 "/usr/include/stdio.h" 3 4
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) ;

# 658 "/usr/include/stdio.h" 3 4
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);

# 730 "/usr/include/stdio.h" 3 4
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);

# 766 "/usr/include/stdio.h" 3 4
extern int fseeko (FILE *__stream, __off_t __off, int __whence);




extern __off_t ftello (FILE *__stream) ;
# 785 "/usr/include/stdio.h" 3 4






extern int fgetpos (FILE *__restrict __stream, fpos_t *__restrict __pos);




extern int fsetpos (FILE *__stream, __const fpos_t *__pos);
# 808 "/usr/include/stdio.h" 3 4

# 817 "/usr/include/stdio.h" 3 4


extern void clearerr (FILE *__stream) __attribute__ ((__nothrow__));

extern int feof (FILE *__stream) __attribute__ ((__nothrow__)) ;

extern int ferror (FILE *__stream) __attribute__ ((__nothrow__)) ;




extern void clearerr_unlocked (FILE *__stream) __attribute__ ((__nothrow__));
extern int feof_unlocked (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern int ferror_unlocked (FILE *__stream) __attribute__ ((__nothrow__)) ;








extern void perror (__const char *__s);






# 1 "/usr/include/bits/sys_errlist.h" 1 3 4
# 27 "/usr/include/bits/sys_errlist.h" 3 4
extern int sys_nerr;
extern __const char *__const sys_errlist[];
# 847 "/usr/include/stdio.h" 2 3 4




extern int fileno (FILE *__stream) __attribute__ ((__nothrow__)) ;




extern int fileno_unlocked (FILE *__stream) __attribute__ ((__nothrow__)) ;
# 866 "/usr/include/stdio.h" 3 4
extern FILE *popen (__const char *__command, __const char *__modes) ;





extern int pclose (FILE *__stream);





extern char *ctermid (char *__s) __attribute__ ((__nothrow__));
# 906 "/usr/include/stdio.h" 3 4
extern void flockfile (FILE *__stream) __attribute__ ((__nothrow__));



extern int ftrylockfile (FILE *__stream) __attribute__ ((__nothrow__)) ;


extern void funlockfile (FILE *__stream) __attribute__ ((__nothrow__));
# 936 "/usr/include/stdio.h" 3 4

# 2 "hello.c" 2

int main()
{
 printf("Hello,world\n");
 return 0;
}
posted @ 2010-12-26 14:37  Codefor  阅读(2830)  评论(0编辑  收藏  举报