舉個例子來說：
正常的定義一個結構體 的過程是

typdef struct __str__Student {char* name;int id; }Student;

但是當大量的使用結構體定義的時候會出現定義顯得過于麻煩，巧妙的使用 ## 連接符能夠很好的解決這個問題如下：

#include <stdio.h>#define STRUCT(type) typedef struct _tag_##type type;\ struct _tag_##typeSTRUCT(Student) //當一個工程中有大量的結構體的時候，這樣使用能夠節省大量的時間 {char* name;int id; };int main() {Student s1;Student s2;s1.name = "s1";s1.id = 0;s2.name = "s2";s2.id = 1;printf("%s\n", s1.name);printf("%d\n", s1.id);printf("%s\n", s2.name);printf("%d\n", s2.id);return 0; }

在linux上按照單步編譯 gcc -E test.c -0 test.i 結果如下：
test.i輸出：
在test.i中前面的都是stdio.h中的文件，不需要看直接看后面的就是上述連接符處理的過程：

# 1 "aa.c" # 1 "<built-in>" # 1 "<command-line>" # 1 "/usr/include/stdc-predef.h" 1 3 4 # 1 "<command-line>" 2 # 1 "aa.c" # 1 "/usr/include/stdio.h" 1 3 4 # 27 "/usr/include/stdio.h" 3 4 # 1 "/usr/include/features.h" 1 3 4 # 367 "/usr/include/features.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 1 3 4 # 410 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4 # 411 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 2 3 4 # 368 "/usr/include/features.h" 2 3 4 # 391 "/usr/include/features.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 1 3 4 # 10 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/gnu/stubs-64.h" 1 3 4 # 11 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 2 3 4 # 392 "/usr/include/features.h" 2 3 4 # 28 "/usr/include/stdio.h" 2 3 4# 1 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef.h" 1 3 4 # 216 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef.h" 3 4# 216 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef.h" 3 4 typedef long unsigned int size_t; # 34 "/usr/include/stdio.h" 2 3 4# 1 "/usr/include/x86_64-linux-gnu/bits/types.h" 1 3 4 # 27 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4 # 28 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4typedef 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;typedef signed long int __int64_t; typedef unsigned long int __uint64_t;typedef long int __quad_t; typedef unsigned long int __u_quad_t; # 121 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/bits/typesizes.h" 1 3 4 # 122 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4typedef unsigned long int __dev_t; typedef unsigned int __uid_t; typedef unsigned int __gid_t; typedef unsigned long int __ino_t; typedef unsigned long int __ino64_t; typedef unsigned int __mode_t; typedef unsigned long int __nlink_t; typedef long int __off_t; typedef long int __off64_t; typedef int __pid_t; typedef struct { int __val[2]; } __fsid_t; typedef long int __clock_t; typedef unsigned long int __rlim_t; typedef unsigned long int __rlim64_t; typedef unsigned int __id_t; typedef long int __time_t; typedef unsigned int __useconds_t; typedef long int __suseconds_t;typedef int __daddr_t; typedef int __key_t;typedef int __clockid_t;typedef void * __timer_t;typedef long int __blksize_t;typedef long int __blkcnt_t; typedef long int __blkcnt64_t;typedef unsigned long int __fsblkcnt_t; typedef unsigned long int __fsblkcnt64_t;typedef unsigned long int __fsfilcnt_t; typedef unsigned long int __fsfilcnt64_t;typedef long int __fsword_t;typedef long int __ssize_t;typedef long int __syscall_slong_t;typedef unsigned long int __syscall_ulong_t;typedef __off64_t __loff_t; typedef __quad_t *__qaddr_t; typedef char *__caddr_t;typedef long int __intptr_t;typedef unsigned int __socklen_t; # 36 "/usr/include/stdio.h" 2 3 4 # 44 "/usr/include/stdio.h" 3 4 struct _IO_FILE;typedef struct _IO_FILE FILE;# 64 "/usr/include/stdio.h" 3 4 typedef struct _IO_FILE __FILE; # 74 "/usr/include/stdio.h" 3 4 # 1 "/usr/include/libio.h" 1 3 4 # 31 "/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/x86_64-linux-gnu/5/include/stddef.h" 1 3 4 # 16 "/usr/include/_G_config.h" 2 3 4# 1 "/usr/include/wchar.h" 1 3 4 # 82 "/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; # 32 "/usr/include/libio.h" 2 3 4 # 49 "/usr/include/libio.h" 3 4 # 1 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stdarg.h" 1 3 4 # 40 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stdarg.h" 3 4 typedef __builtin_va_list __gnuc_va_list; # 50 "/usr/include/libio.h" 2 3 4 # 144 "/usr/include/libio.h" 3 4 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; # 173 "/usr/include/libio.h" 3 4 };enum __codecvt_result {__codecvt_ok,__codecvt_partial,__codecvt_error,__codecvt_noconv }; # 241 "/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; # 289 "/usr/include/libio.h" 3 4__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)];};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_; # 333 "/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); # 385 "/usr/include/libio.h" 3 4 extern int __underflow (_IO_FILE *); extern int __uflow (_IO_FILE *); extern int __overflow (_IO_FILE *, int); # 429 "/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__ , __leaf__)); extern int _IO_ferror (_IO_FILE *__fp) __attribute__ ((__nothrow__ , __leaf__));extern int _IO_peekc_locked (_IO_FILE *__fp);extern void _IO_flockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__)); extern void _IO_funlockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__)); extern int _IO_ftrylockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__)); # 459 "/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__ , __leaf__)); # 75 "/usr/include/stdio.h" 2 3 4typedef __gnuc_va_list va_list; # 90 "/usr/include/stdio.h" 3 4 typedef __off_t off_t; # 102 "/usr/include/stdio.h" 3 4 typedef __ssize_t ssize_t;typedef _G_fpos_t fpos_t;# 164 "/usr/include/stdio.h" 3 4 # 1 "/usr/include/x86_64-linux-gnu/bits/stdio_lim.h" 1 3 4 # 165 "/usr/include/stdio.h" 2 3 4extern struct _IO_FILE *stdin; extern struct _IO_FILE *stdout; extern struct _IO_FILE *stderr;extern int remove (const char *__filename) __attribute__ ((__nothrow__ , __leaf__));extern int rename (const char *__old, const char *__new) __attribute__ ((__nothrow__ , __leaf__));extern int renameat (int __oldfd, const char *__old, int __newfd,const char *__new) __attribute__ ((__nothrow__ , __leaf__));extern FILE *tmpfile (void) ; # 209 "/usr/include/stdio.h" 3 4 extern char *tmpnam (char *__s) __attribute__ ((__nothrow__ , __leaf__)) ;extern char *tmpnam_r (char *__s) __attribute__ ((__nothrow__ , __leaf__)) ; # 227 "/usr/include/stdio.h" 3 4 extern char *tempnam (const char *__dir, const char *__pfx)__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) ;extern int fclose (FILE *__stream);extern int fflush (FILE *__stream);# 252 "/usr/include/stdio.h" 3 4 extern int fflush_unlocked (FILE *__stream); # 266 "/usr/include/stdio.h" 3 4extern FILE *fopen (const char *__restrict __filename,const char *__restrict __modes) ;extern FILE *freopen (const char *__restrict __filename,const char *__restrict __modes,FILE *__restrict __stream) ; # 295 "/usr/include/stdio.h" 3 4# 306 "/usr/include/stdio.h" 3 4 extern FILE *fdopen (int __fd, const char *__modes) __attribute__ ((__nothrow__ , __leaf__)) ; # 319 "/usr/include/stdio.h" 3 4 extern FILE *fmemopen (void *__s, size_t __len, const char *__modes)__attribute__ ((__nothrow__ , __leaf__)) ;extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) __attribute__ ((__nothrow__ , __leaf__)) ;extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __attribute__ ((__nothrow__ , __leaf__));extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,int __modes, size_t __n) __attribute__ ((__nothrow__ , __leaf__));extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,size_t __size) __attribute__ ((__nothrow__ , __leaf__));extern void setlinebuf (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));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)));# 412 "/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__ , __leaf__)); # 443 "/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__ , __leaf__)); # 463 "/usr/include/stdio.h" 3 4extern 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__ , __leaf__)) __attribute__ ((__format__ (__scanf__, 2, 0))); # 494 "/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__ , __leaf__))__attribute__ ((__format__ (__scanf__, 2, 0))); # 522 "/usr/include/stdio.h" 3 4extern int fgetc (FILE *__stream); extern int getc (FILE *__stream);extern int getchar (void);# 550 "/usr/include/stdio.h" 3 4 extern int getc_unlocked (FILE *__stream); extern int getchar_unlocked (void); # 561 "/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);# 594 "/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); # 640 "/usr/include/stdio.h" 3 4# 665 "/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);# 737 "/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);# 773 "/usr/include/stdio.h" 3 4 extern int fseeko (FILE *__stream, __off_t __off, int __whence);extern __off_t ftello (FILE *__stream) ; # 792 "/usr/include/stdio.h" 3 4extern int fgetpos (FILE *__restrict __stream, fpos_t *__restrict __pos);extern int fsetpos (FILE *__stream, const fpos_t *__pos); # 815 "/usr/include/stdio.h" 3 4# 824 "/usr/include/stdio.h" 3 4extern void clearerr (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));extern int feof (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;extern int ferror (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;extern void clearerr_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)); extern int feof_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ; extern int ferror_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;extern void perror (const char *__s);# 1 "/usr/include/x86_64-linux-gnu/bits/sys_errlist.h" 1 3 4 # 26 "/usr/include/x86_64-linux-gnu/bits/sys_errlist.h" 3 4 extern int sys_nerr; extern const char *const sys_errlist[]; # 854 "/usr/include/stdio.h" 2 3 4extern int fileno (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;extern int fileno_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ; # 872 "/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__ , __leaf__)); # 912 "/usr/include/stdio.h" 3 4 extern void flockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));extern int ftrylockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;extern void funlockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)); # 942 "/usr/include/stdio.h" 3 4# 2 "aa.c" 2--------------------這里就是##連接符處理的過程 是不是發現巧妙的使用##連接符能夠很好的降低工作量 提高工作效率 # 6 "aa.c" typedef struct _tag_Student Student;struct _tag_Student {char* name;int id; };int main() {Student s1;Student s2;s1.name = "s1";s1.id = 0;s2.name = "s2";s2.id = 1;printf("%s\n", s1.name);printf("%d\n", s1.id);printf("%s\n", s2.name);printf("%d\n", s2.id);return 0; }

總結

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