Clever Use of the C language # And # (example), clever use of the C Language

Clever Use of the C language # And # (example), clever use of the C Language

For example:

The normal process of defining a struct is

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

However, when a large number of struct definitions are used, the definition is too troublesome. The clever use of the # connector can solve the problem as follows:

# Include <stdio. h> # define STRUCT (type) typedef struct _ tag _ # type; \ struct _ tag _ # typeSTRUCT (Student) // when a project contains a large number of struct, this can save a lot of time {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 ;}

On linux, compile gcc-E test. c-0 test. I in one step. The result is as follows:

Test. I output:

All files in stdio. h are in front of test. I. You do not need to check whether the following is the process of handling the above connector:

#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 3 4 #216"/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef. h & quot; 3 4 #216 & quot;/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 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; 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 & quot; 1 3 4 #122 & quot;/usr/include/x86_64-linux-gnu/bits/types. h "2 3 4 typedef 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 _ forward; typedef unsigned long int _ fsblkcnt_t; typedef unsigned long int _ forward; 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 _ struct; 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 _ character Buf [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; struct _ IO_FILE_plus; extern struct _ IO_FILE_plus _ IO_2_1_stdin _; extern struct _ IO_FILE_plus _ Empty _; #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 _ partition (_ 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 4 typedef _ gnuc_va_list va_list; #90"/usr/include/stdio. h "3 4 typedef _ off_t; #102"/usr/include/stdio. h "3 4 typedef _ 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 4 extern 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 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 ); #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 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 _, _ 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 4 extern 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 4 extern 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 4 extern 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 4 extern 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 -------------------- here is # Is the handling process of the connector found clever use # the connector can greatly reduce the workload and improve work efficiency #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 ;}