1. gcc -E hello.c -o hello.i

或者写为:

  1. gcc -E hello.c

-E 表示可以让编译器在预处理后停止，并输出预处理结果。

可以输出 hello.i ，hello.i 文件中存放着 hello.c 经预处理之后的代码。 打开 hello.i 文件，看一看 就明白了。 其中 hello.i 的文件内容如下:

  1. # 1 "hello.c"
  2. # 1 "<built-in>"
  3. # 1 "<命令行>"
  4. # 1 "hello.c"
  5. # 1 "/usr/include/stdio.h" 1 3 4
  6. # 28 "/usr/include/stdio.h" 3 4
  7. # 1 "/usr/include/features.h" 1 3 4
  8. # 324 "/usr/include/features.h" 3 4
  9. # 1 "/usr/include/i386-linux-gnu/bits/predefs.h" 1 3 4
  10. # 325 "/usr/include/features.h" 2 3 4
  11. # 357 "/usr/include/features.h" 3 4
  12. # 1 "/usr/include/i386-linux-gnu/sys/cdefs.h" 1 3 4
  13. # 378 "/usr/include/i386-linux-gnu/sys/cdefs.h" 3 4
  14. # 1 "/usr/include/i386-linux-gnu/bits/wordsize.h" 1 3 4
  15. # 379 "/usr/include/i386-linux-gnu/sys/cdefs.h" 2 3 4
  16. # 358 "/usr/include/features.h" 2 3 4
  17. # 389 "/usr/include/features.h" 3 4
  18. # 1 "/usr/include/i386-linux-gnu/gnu/stubs.h" 1 3 4
  22. # 1 "/usr/include/i386-linux-gnu/bits/wordsize.h" 1 3 4
  23. # 5 "/usr/include/i386-linux-gnu/gnu/stubs.h" 2 3 4
  26. # 1 "/usr/include/i386-linux-gnu/gnu/stubs-32.h" 1 3 4
  27. # 8 "/usr/include/i386-linux-gnu/gnu/stubs.h" 2 3 4
  28. # 390 "/usr/include/features.h" 2 3 4
  29. # 29 "/usr/include/stdio.h" 2 3 4
  35. # 1 "/usr/lib/gcc/i686-linux-gnu/4.6/include/stddef.h" 1 3 4
  36. # 212 "/usr/lib/gcc/i686-linux-gnu/4.6/include/stddef.h" 3 4
  37. typedef unsigned int size_t;
  38. # 35 "/usr/include/stdio.h" 2 3 4
  40. # 1 "/usr/include/i386-linux-gnu/bits/types.h" 1 3 4
  41. # 28 "/usr/include/i386-linux-gnu/bits/types.h" 3 4
  42. # 1 "/usr/include/i386-linux-gnu/bits/wordsize.h" 1 3 4
  43. # 29 "/usr/include/i386-linux-gnu/bits/types.h" 2 3 4
  46. typedef unsigned char __u_char;
  47. typedef unsigned short int __u_short;
  48. typedef unsigned int __u_int;
  49. typedef unsigned long int __u_long;
  52. typedef signed char __int8_t;
  53. typedef unsigned char __uint8_t;
  54. typedef signed short int __int16_t;
  55. typedef unsigned short int __uint16_t;
  56. typedef signed int __int32_t;
  57. typedef unsigned int __uint32_t;
  62. __extension__ typedef signed long long int __int64_t;
  63. __extension__ typedef unsigned long long int __uint64_t;
  71. __extension__ typedef long long int __quad_t;
  72. __extension__ typedef unsigned long long int __u_quad_t;
  73. # 131 "/usr/include/i386-linux-gnu/bits/types.h" 3 4
  74. # 1 "/usr/include/i386-linux-gnu/bits/typesizes.h" 1 3 4
  75. # 132 "/usr/include/i386-linux-gnu/bits/types.h" 2 3 4
  78. __extension__ typedef __u_quad_t __dev_t;
  79. __extension__ typedef unsigned int __uid_t;
  80. __extension__ typedef unsigned int __gid_t;
  81. __extension__ typedef unsigned long int __ino_t;
  82. __extension__ typedef __u_quad_t __ino64_t;
  83. __extension__ typedef unsigned int __mode_t;
  84. __extension__ typedef unsigned int __nlink_t;
  85. __extension__ typedef long int __off_t;
  86. __extension__ typedef __quad_t __off64_t;
  87. __extension__ typedef int __pid_t;
  88. __extension__ typedef struct { int __val[2]; } __fsid_t;
  89. __extension__ typedef long int __clock_t;
  90. __extension__ typedef unsigned long int __rlim_t;
  91. __extension__ typedef __u_quad_t __rlim64_t;
  92. __extension__ typedef unsigned int __id_t;
  93. __extension__ typedef long int __time_t;
  94. __extension__ typedef unsigned int __useconds_t;
  95. __extension__ typedef long int __suseconds_t;
  97. __extension__ typedef int __daddr_t;
  98. __extension__ typedef long int __swblk_t;
  99. __extension__ typedef int __key_t;
  102. __extension__ typedef int __clockid_t;
  105. __extension__ typedef void * __timer_t;
  108. __extension__ typedef long int __blksize_t;
  113. __extension__ typedef long int __blkcnt_t;
  114. __extension__ typedef __quad_t __blkcnt64_t;
  117. __extension__ typedef unsigned long int __fsblkcnt_t;
  118. __extension__ typedef __u_quad_t __fsblkcnt64_t;
  121. __extension__ typedef unsigned long int __fsfilcnt_t;
  122. __extension__ typedef __u_quad_t __fsfilcnt64_t;
  124. __extension__ typedef int __ssize_t;
  128. typedef __off64_t __loff_t;
  129. typedef __quad_t *__qaddr_t;
  130. typedef char *__caddr_t;
  133. __extension__ typedef int __intptr_t;
  136. __extension__ typedef unsigned int __socklen_t;
  137. # 37 "/usr/include/stdio.h" 2 3 4
  138. # 45 "/usr/include/stdio.h" 3 4
  139. struct _IO_FILE;
  143. typedef struct _IO_FILE FILE;
  149. # 65 "/usr/include/stdio.h" 3 4
  150. typedef struct _IO_FILE __FILE;
  151. # 75 "/usr/include/stdio.h" 3 4
  152. # 1 "/usr/include/libio.h" 1 3 4
  153. # 32 "/usr/include/libio.h" 3 4
  154. # 1 "/usr/include/_G_config.h" 1 3 4
  155. # 15 "/usr/include/_G_config.h" 3 4
  156. # 1 "/usr/lib/gcc/i686-linux-gnu/4.6/include/stddef.h" 1 3 4
  157. # 16 "/usr/include/_G_config.h" 2 3 4
  162. # 1 "/usr/include/wchar.h" 1 3 4
  163. # 83 "/usr/include/wchar.h" 3 4
  164. typedef struct
  165. {
  166.   int __count;
  167.   union
  168.   {
  170.     unsigned int __wch;
  174.     char __wchb[4];
  175.   } __value;
  176. } __mbstate_t;
  177. # 21 "/usr/include/_G_config.h" 2 3 4
  179. typedef struct
  180. {
  181.   __off_t __pos;
  182.   __mbstate_t __state;
  183. } _G_fpos_t;
  184. typedef struct
  185. {
  186.   __off64_t __pos;
  187.   __mbstate_t __state;
  188. } _G_fpos64_t;
  189. # 53 "/usr/include/_G_config.h" 3 4
  190. typedef int _G_int16_t __attribute__ ((__mode__ (__HI__)));
  191. typedef int _G_int32_t __attribute__ ((__mode__ (__SI__)));
  192. typedef unsigned int _G_uint16_t __attribute__ ((__mode__ (__HI__)));
  193. typedef unsigned int _G_uint32_t __attribute__ ((__mode__ (__SI__)));
  194. # 33 "/usr/include/libio.h" 2 3 4
  195. # 53 "/usr/include/libio.h" 3 4
  196. # 1 "/usr/lib/gcc/i686-linux-gnu/4.6/include/stdarg.h" 1 3 4
  197. # 40 "/usr/lib/gcc/i686-linux-gnu/4.6/include/stdarg.h" 3 4
  198. typedef __builtin_va_list __gnuc_va_list;
  199. # 54 "/usr/include/libio.h" 2 3 4
  200. # 172 "/usr/include/libio.h" 3 4
  201. struct _IO_jump_t; struct _IO_FILE;
  202. # 182 "/usr/include/libio.h" 3 4
  203. typedef void _IO_lock_t;
  209. struct _IO_marker {
  210.   struct _IO_marker *_next;
  211.   struct _IO_FILE *_sbuf;
  215.   int _pos;
  216. # 205 "/usr/include/libio.h" 3 4
  217. };
  220. enum __codecvt_result
  221. {
  222.   __codecvt_ok,
  223.   __codecvt_partial,
  224.   __codecvt_error,
  225.   __codecvt_noconv
  226. };
  227. # 273 "/usr/include/libio.h" 3 4
  228. struct _IO_FILE {
  229.   int _flags;
  234.   char* _IO_read_ptr;
  235.   char* _IO_read_end;
  236.   char* _IO_read_base;
  237.   char* _IO_write_base;
  238.   char* _IO_write_ptr;
  239.   char* _IO_write_end;
  240.   char* _IO_buf_base;
  241.   char* _IO_buf_end;
  243.   char *_IO_save_base;
  244.   char *_IO_backup_base;
  245.   char *_IO_save_end;
  247.   struct _IO_marker *_markers;
  249.   struct _IO_FILE *_chain;
  251.   int _fileno;
  255.   int _flags2;
  257.   __off_t _old_offset;
  261.   unsigned short _cur_column;
  262.   signed char _vtable_offset;
  263.   char _shortbuf[1];
  267.   _IO_lock_t *_lock;
  268. # 321 "/usr/include/libio.h" 3 4
  269.   __off64_t _offset;
  270. # 330 "/usr/include/libio.h" 3 4
  271.   void *__pad1;
  272.   void *__pad2;
  273.   void *__pad3;
  274.   void *__pad4;
  275.   size_t __pad5;
  277.   int _mode;
  279.   char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
  281. };
  284. typedef struct _IO_FILE _IO_FILE;
  287. struct _IO_FILE_plus;
  289. extern struct _IO_FILE_plus _IO_2_1_stdin_;
  290. extern struct _IO_FILE_plus _IO_2_1_stdout_;
  291. extern struct _IO_FILE_plus _IO_2_1_stderr_;
  292. # 366 "/usr/include/libio.h" 3 4
  293. typedef __ssize_t __io_read_fn (void *__cookie, char *__buf, size_t __nbytes);
  301. typedef __ssize_t __io_write_fn (void *__cookie, __const char *__buf,
  302.      size_t __n);
  310. typedef int __io_seek_fn (void *__cookie, __off64_t *__pos, int __w);
  313. typedef int __io_close_fn (void *__cookie);
  314. # 418 "/usr/include/libio.h" 3 4
  315. extern int __underflow (_IO_FILE *);
  316. extern int __uflow (_IO_FILE *);
  317. extern int __overflow (_IO_FILE *, int);
  318. # 462 "/usr/include/libio.h" 3 4
  319. extern int _IO_getc (_IO_FILE *__fp);
  320. extern int _IO_putc (int __c, _IO_FILE *__fp);
  321. extern int _IO_feof (_IO_FILE *__fp) __attribute__ ((__nothrow__ , __leaf__));
  322. extern int _IO_ferror (_IO_FILE *__fp) __attribute__ ((__nothrow__ , __leaf__));
  324. extern int _IO_peekc_locked (_IO_FILE *__fp);
  330. extern void _IO_flockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
  331. extern void _IO_funlockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
  332. extern int _IO_ftrylockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
  333. # 492 "/usr/include/libio.h" 3 4
  334. extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict,
  335.    __gnuc_va_list, int *__restrict);
  336. extern int _IO_vfprintf (_IO_FILE *__restrict, const char *__restrict,
  337.     __gnuc_va_list);
  338. extern __ssize_t _IO_padn (_IO_FILE *, int, __ssize_t);
  339. extern size_t _IO_sgetn (_IO_FILE *, void *, size_t);
  341. extern __off64_t _IO_seekoff (_IO_FILE *, __off64_t, int, int);
  342. extern __off64_t _IO_seekpos (_IO_FILE *, __off64_t, int);
  344. extern void _IO_free_backup_area (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
  345. # 76 "/usr/include/stdio.h" 2 3 4
  350. typedef __gnuc_va_list va_list;
  351. # 91 "/usr/include/stdio.h" 3 4
  352. typedef __off_t off_t;
  353. # 103 "/usr/include/stdio.h" 3 4
  354. typedef __ssize_t ssize_t;
  362. typedef _G_fpos_t fpos_t;
  367. # 165 "/usr/include/stdio.h" 3 4
  368. # 1 "/usr/include/i386-linux-gnu/bits/stdio_lim.h" 1 3 4
  369. # 166 "/usr/include/stdio.h" 2 3 4
  373. extern struct _IO_FILE *stdin;
  374. extern struct _IO_FILE *stdout;
  375. extern struct _IO_FILE *stderr;
  383. extern int remove (__const char *__filename) __attribute__ ((__nothrow__ , __leaf__));
  385. extern int rename (__const char *__old, __const char *__new) __attribute__ ((__nothrow__ , __leaf__));
  390. extern int renameat (int __oldfd, __const char *__old, int __newfd,
  391.        __const char *__new) __attribute__ ((__nothrow__ , __leaf__));
  400. extern FILE *tmpfile (void) ;
  401. # 210 "/usr/include/stdio.h" 3 4
  402. extern char *tmpnam (char *__s) __attribute__ ((__nothrow__ , __leaf__)) ;
  408. extern char *tmpnam_r (char *__s) __attribute__ ((__nothrow__ , __leaf__)) ;
  409. # 228 "/usr/include/stdio.h" 3 4
  410. extern char *tempnam (__const char *__dir, __const char *__pfx)
  411.      __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) ;
  420. extern int fclose (FILE *__stream);
  425. extern int fflush (FILE *__stream);
  427. # 253 "/usr/include/stdio.h" 3 4
  428. extern int fflush_unlocked (FILE *__stream);
  429. # 267 "/usr/include/stdio.h" 3 4
  436. extern FILE *fopen (__const char *__restrict __filename,
  437.       __const char *__restrict __modes) ;
  442. extern FILE *freopen (__const char *__restrict __filename,
  443.         __const char *__restrict __modes,
  444.         FILE *__restrict __stream) ;
  445. # 296 "/usr/include/stdio.h" 3 4
  447. # 307 "/usr/include/stdio.h" 3 4
  448. extern FILE *fdopen (int __fd, __const char *__modes) __attribute__ ((__nothrow__ , __leaf__)) ;
  449. # 320 "/usr/include/stdio.h" 3 4
  450. extern FILE *fmemopen (void *__s, size_t __len, __const char *__modes)
  451.   __attribute__ ((__nothrow__ , __leaf__)) ;
  456. extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) __attribute__ ((__nothrow__ , __leaf__)) ;
  463. extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __attribute__ ((__nothrow__ , __leaf__));
  467. extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,
  468.       int __modes, size_t __n) __attribute__ ((__nothrow__ , __leaf__));
  474. extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,
  475.          size_t __size) __attribute__ ((__nothrow__ , __leaf__));
  478. extern void setlinebuf (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
  487. extern int fprintf (FILE *__restrict __stream,
  488.       __const char *__restrict __format, ...);
  493. extern int printf (__const char *__restrict __format, ...);
  495. extern int sprintf (char *__restrict __s,
  496.       __const char *__restrict __format, ...) __attribute__ ((__nothrow__));
  502. extern int vfprintf (FILE *__restrict __s, __const char *__restrict __format,
  503.        __gnuc_va_list __arg);
  508. extern int vprintf (__const char *__restrict __format, __gnuc_va_list __arg);
  510. extern int vsprintf (char *__restrict __s, __const char *__restrict __format,
  511.        __gnuc_va_list __arg) __attribute__ ((__nothrow__));
  517. extern int snprintf (char *__restrict __s, size_t __maxlen,
  518.        __const char *__restrict __format, ...)
  519.      __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 4)));
  521. extern int vsnprintf (char *__restrict __s, size_t __maxlen,
  522.         __const char *__restrict __format, __gnuc_va_list __arg)
  523.      __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 0)));
  525. # 418 "/usr/include/stdio.h" 3 4
  526. extern int vdprintf (int __fd, __const char *__restrict __fmt,
  527.        __gnuc_va_list __arg)
  528.      __attribute__ ((__format__ (__printf__, 2, 0)));
  529. extern int dprintf (int __fd, __const char *__restrict __fmt, ...)
  530.      __attribute__ ((__format__ (__printf__, 2, 3)));
  539. extern int fscanf (FILE *__restrict __stream,
  540.      __const char *__restrict __format, ...) ;
  545. extern int scanf (__const char *__restrict __format, ...) ;
  547. extern int sscanf (__const char *__restrict __s,
  548.      __const char *__restrict __format, ...) __attribute__ ((__nothrow__ , __leaf__));
  549. # 449 "/usr/include/stdio.h" 3 4
  550. extern int fscanf (FILE *__restrict __stream, __const char *__restrict __format, ...) __asm__ ("" "__isoc99_fscanf")
  552.                                ;
  553. extern int scanf (__const char *__restrict __format, ...) __asm__ ("" "__isoc99_scanf")
  554.                               ;
  555. extern int sscanf (__const char *__restrict __s, __const char *__restrict __format, ...) __asm__ ("" "__isoc99_sscanf") __attribute__ ((__nothrow__ , __leaf__))
  557.                       ;
  558. # 469 "/usr/include/stdio.h" 3 4
  567. extern int vfscanf (FILE *__restrict __s, __const char *__restrict __format,
  568.       __gnuc_va_list __arg)
  569.      __attribute__ ((__format__ (__scanf__, 2, 0))) ;
  575. extern int vscanf (__const char *__restrict __format, __gnuc_va_list __arg)
  576.      __attribute__ ((__format__ (__scanf__, 1, 0))) ;
  579. extern int vsscanf (__const char *__restrict __s,
  580.       __const char *__restrict __format, __gnuc_va_list __arg)
  581.      __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__format__ (__scanf__, 2, 0)));
  582. # 500 "/usr/include/stdio.h" 3 4
  583. extern int vfscanf (FILE *__restrict __s, __const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vfscanf")
  587.      __attribute__ ((__format__ (__scanf__, 2, 0))) ;
  588. extern int vscanf (__const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vscanf")
  590.      __attribute__ ((__format__ (__scanf__, 1, 0))) ;
  591. extern int vsscanf (__const char *__restrict __s, __const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vsscanf") __attribute__ ((__nothrow__ , __leaf__))
  595.      __attribute__ ((__format__ (__scanf__, 2, 0)));
  596. # 528 "/usr/include/stdio.h" 3 4
  606. extern int fgetc (FILE *__stream);
  607. extern int getc (FILE *__stream);
  613. extern int getchar (void);
  615. # 556 "/usr/include/stdio.h" 3 4
  616. extern int getc_unlocked (FILE *__stream);
  617. extern int getchar_unlocked (void);
  618. # 567 "/usr/include/stdio.h" 3 4
  619. extern int fgetc_unlocked (FILE *__stream);
  631. extern int fputc (int __c, FILE *__stream);
  632. extern int putc (int __c, FILE *__stream);
  638. extern int putchar (int __c);
  640. # 600 "/usr/include/stdio.h" 3 4
  641. extern int fputc_unlocked (int __c, FILE *__stream);
  649. extern int putc_unlocked (int __c, FILE *__stream);
  650. extern int putchar_unlocked (int __c);
  657. extern int getw (FILE *__stream);
  660. extern int putw (int __w, FILE *__stream);
  669. extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
  670.      ;
  677. extern char *gets (char *__s) ;
  679. # 662 "/usr/include/stdio.h" 3 4
  680. extern __ssize_t __getdelim (char **__restrict __lineptr,
  681.           size_t *__restrict __n, int __delimiter,
  682.           FILE *__restrict __stream) ;
  683. extern __ssize_t getdelim (char **__restrict __lineptr,
  684.         size_t *__restrict __n, int __delimiter,
  685.         FILE *__restrict __stream) ;
  693. extern __ssize_t getline (char **__restrict __lineptr,
  694.        size_t *__restrict __n,
  695.        FILE *__restrict __stream) ;
  704. extern int fputs (__const char *__restrict __s, FILE *__restrict __stream);
  710. extern int puts (__const char *__s);
  717. extern int ungetc (int __c, FILE *__stream);
  724. extern size_t fread (void *__restrict __ptr, size_t __size,
  725.        size_t __n, FILE *__restrict __stream) ;
  730. extern size_t fwrite (__const void *__restrict __ptr, size_t __size,
  731.         size_t __n, FILE *__restrict __s);
  733. # 734 "/usr/include/stdio.h" 3 4
  734. extern size_t fread_unlocked (void *__restrict __ptr, size_t __size,
  735.          size_t __n, FILE *__restrict __stream) ;
  736. extern size_t fwrite_unlocked (__const void *__restrict __ptr, size_t __size,
  737.           size_t __n, FILE *__restrict __stream);
  746. extern int fseek (FILE *__stream, long int __off, int __whence);
  751. extern long int ftell (FILE *__stream) ;
  756. extern void rewind (FILE *__stream);
  758. # 770 "/usr/include/stdio.h" 3 4
  759. extern int fseeko (FILE *__stream, __off_t __off, int __whence);
  764. extern __off_t ftello (FILE *__stream) ;
  765. # 789 "/usr/include/stdio.h" 3 4
  772. extern int fgetpos (FILE *__restrict __stream, fpos_t *__restrict __pos);
  777. extern int fsetpos (FILE *__stream, __const fpos_t *__pos);
  778. # 812 "/usr/include/stdio.h" 3 4
  780. # 821 "/usr/include/stdio.h" 3 4
  783. extern void clearerr (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
  785. extern int feof (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  787. extern int ferror (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  792. extern void clearerr_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
  793. extern int feof_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  794. extern int ferror_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  803. extern void perror (__const char *__s);
  810. # 1 "/usr/include/i386-linux-gnu/bits/sys_errlist.h" 1 3 4
  811. # 27 "/usr/include/i386-linux-gnu/bits/sys_errlist.h" 3 4
  812. extern int sys_nerr;
  813. extern __const char *__const sys_errlist[];
  814. # 851 "/usr/include/stdio.h" 2 3 4
  819. extern int fileno (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  824. extern int fileno_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  825. # 870 "/usr/include/stdio.h" 3 4
  826. extern FILE *popen (__const char *__command, __const char *__modes) ;
  832. extern int pclose (FILE *__stream);
  838. extern char *ctermid (char *__s) __attribute__ ((__nothrow__ , __leaf__));
  839. # 910 "/usr/include/stdio.h" 3 4
  840. extern void flockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
  844. extern int ftrylockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
  847. extern void funlockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
  848. # 940 "/usr/include/stdio.h" 3 4
  850. # 2 "hello.c" 2
  852. int main(void)
  853. {
  854.     printf("Hello World!\n");
  855.     return 0;
  856. }

后面那条指令，是直接在命令行窗口中输出预处理后的代码. 在本例中，预处理的结果就是将 stdio.h 文件中的内容插入到 hello.c 中了。