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; }
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