OFFSETOF

简单来两个：

 

#include <stdio.h> #include <string.h> typedef unsigned char BYTE; #define MAXMEMALLOCLEN 16384L #define MAXSTRLEN 16384L #define MAX_DB_PAGESIZE 16384L #define MEMMOVE(s, d, n) / memmove_sanity((BYTE *)(s), (BYTE *)(d),(unsigned int)(n), / (unsigned int)(MAXMEMALLOCLEN), / __FILE__, __LINE__) void memmove_sanity (BYTE *s, BYTE *d, unsigned int len, unsigned int maxlen, char *file, int line) { strncpy((char *)d, (char *)s, len); } //typedef unsigned int size_t; typedef unsigned short uint16; typedef struct txcomp_dblk { BYTE tcd_stat; /* status word */ BYTE tcd_spare; /* UNUSED */ uint16 tcd_len; /* length of the (un)compressed data block. */ uint16 tcd_orig_bytes; /* # bytes of original text data compressed ** into this block. */ uint16 tcd_orig_chars; /* # characters of original text data ** compressed into this block. */ BYTE tcd_data[1]; /* Dummy array to mark the start of data */ } TXCOMP_DBLK; #define OFFSETOF(type, struc) ((size_t) (&((type *) NULL)->struc)) #define GETUSHORT(p) (*(uint16 *) (p)) /* Overhead of each data block */ #define TXCOMP_DBLK_HEADSIZE ((uint16) OFFSETOF(TXCOMP_DBLK, tcd_data[0])) /* Get total length of the (un)compressed data block. */ #define TXCOMP_DBLK_LEN(dblkp) GETUSHORT((BYTE *)(dblkp) + / (uint16) OFFSETOF(TXCOMP_DBLK, tcd_len)) /* Get # bytes of original text data compressed into this block. */ #define TXCOMP_DBLK_ORIG_BYTES(dblkp) GETUSHORT((BYTE *)(dblkp) + / (uint16) OFFSETOF(TXCOMP_DBLK, tcd_orig_bytes)) /* Get # chars of original text data compressed into this block. */ #define TXCOMP_DBLK_ORIG_CHARS(dblkp) GETUSHORT((BYTE *)(dblkp) + / (uint16) OFFSETOF(TXCOMP_DBLK, tcd_orig_chars)) /* Get # chars compressed into this block. */ #define TXCOMP_DBLK_GET_CHARS(is_mulibyte, dblkp) / (is_mulibyte ? TXCOMP_DBLK_ORIG_CHARS(dblkp) / : TXCOMP_DBLK_ORIG_BYTES(dblkp)) /* Put total length of the (un)compressed data block. */ #define TXCOMP_DBLK_PUT_LEN(dblkp, length) / MEMMOVE(&length, ((BYTE *)dblkp + (uint16) OFFSETOF(TXCOMP_DBLK, tcd_len)), / sizeof(((TXCOMP_DBLK *)dblkp)->tcd_len)) /* Put # bytes of original text data compressed into this block. */ #define TXCOMP_DBLK_PUT_ORIG_BYTES(dblkp, origin_bytes) / MEMMOVE(&origin_bytes, ((BYTE *)dblkp + (uint16) OFFSETOF(TXCOMP_DBLK, tcd_orig_bytes)), / sizeof(((TXCOMP_DBLK *)dblkp)->tcd_orig_bytes)) /* Put # chars of original text data compressed into this block. */ #define TXCOMP_DBLK_PUT_ORIG_CHARS(dblkp, origin_chars) / MEMMOVE(&origin_chars, ((BYTE *)dblkp + (uint16) OFFSETOF(TXCOMP_DBLK, tcd_orig_chars)), / sizeof(((TXCOMP_DBLK *)dblkp)->tcd_orig_chars)) void main() { /* TXCOMP_DBLK dblk; dblk.tcd_stat =2; dblk.tcd_len = 3; dblk.tcd_orig_bytes = 4; dblk.tcd_orig_chars = 5; int a = (int)TXCOMP_DBLK_HEADSIZE; uint16 b = (int)TXCOMP_DBLK_LEN(&dblk); int c = (int )TXCOMP_DBLK_ORIG_BYTES(&dblk); int d = (int ) TXCOMP_DBLK_ORIG_CHARS(&dblk); printf("a=%d,b=%d,c=%d,d=%d/n",a,b,c,d); uint16 aa = 33; uint16 bb = 44; uint16 cc = 55; TXCOMP_DBLK_PUT_LEN(&dblk,aa); TXCOMP_DBLK_PUT_ORIG_BYTES(&dblk,bb); TXCOMP_DBLK_PUT_ORIG_CHARS(&dblk,cc); a = (int)TXCOMP_DBLK_HEADSIZE; b = (int)TXCOMP_DBLK_LEN(&dblk); c = (int )TXCOMP_DBLK_ORIG_BYTES(&dblk); d = (int ) TXCOMP_DBLK_ORIG_CHARS(&dblk); printf("a=%d,b=%d,c=%d,d=%d/n",a,b,c,d); */ int i; int a,b,c,d; uint16 aa = 37433; uint16 bb = 464; uint16 cc = 5599; BYTE data[20]; for(i =0 ; i<20 ; i++) { data[i]=0; } TXCOMP_DBLK *dblk2 = NULL; dblk2 = (TXCOMP_DBLK *)&data[0]; TXCOMP_DBLK_PUT_LEN(dblk2,aa); TXCOMP_DBLK_PUT_ORIG_BYTES(dblk2,bb); TXCOMP_DBLK_PUT_ORIG_CHARS(dblk2,cc); a = (int)TXCOMP_DBLK_HEADSIZE; b = (int)TXCOMP_DBLK_LEN(dblk2); c = (int )TXCOMP_DBLK_ORIG_BYTES(dblk2); d = (int ) TXCOMP_DBLK_ORIG_CHARS(dblk2); printf("a=%d,b=%d,c=%d,d=%d/n",a,b,c,d); for(i =0 ; i<20 ; i++) { printf("data[%d] is %d/n",i,data[i]); } for(i =0 ; i<20 ; i++) { data[i]=0; } dblk2 = (TXCOMP_DBLK *)&data[1]; TXCOMP_DBLK_PUT_LEN(dblk2,aa); TXCOMP_DBLK_PUT_ORIG_BYTES(dblk2,bb); TXCOMP_DBLK_PUT_ORIG_CHARS(dblk2,cc); a = (int)TXCOMP_DBLK_HEADSIZE; b = (int)TXCOMP_DBLK_LEN(dblk2); c = (int )TXCOMP_DBLK_ORIG_BYTES(dblk2); d = (int ) TXCOMP_DBLK_ORIG_CHARS(dblk2); printf("a=%d,b=%d,c=%d,d=%d/n",a,b,c,d); for(i =0 ; i<20 ; i++) { printf("data[%d] is %d/n",i,data[i]); } for(i =0 ; i<20 ; i++) { data[i]=0; } dblk2 = (TXCOMP_DBLK *)&data[2]; TXCOMP_DBLK_PUT_LEN(dblk2,aa); TXCOMP_DBLK_PUT_ORIG_BYTES(dblk2,bb); TXCOMP_DBLK_PUT_ORIG_CHARS(dblk2,cc); a = (int)TXCOMP_DBLK_HEADSIZE; b = (int)TXCOMP_DBLK_LEN(dblk2); c = (int )TXCOMP_DBLK_ORIG_BYTES(dblk2); d = (int ) TXCOMP_DBLK_ORIG_CHARS(dblk2); printf("a=%d,b=%d,c=%d,d=%d/n",a,b,c,d); for(i =0 ; i<20 ; i++) { printf("data[%d] is %d/n",i,data[i]); } }

 

 

#include <stdio.h> struct person { int age; char name[10]; float number; double y; int x; }; int main() { struct person *uu = NULL; int a = (int)(&(((struct person *)NULL)->age)); int b = (int)(&(((struct person *)0)->name)); int c = (int)(&(((struct person *)NULL)->number)); int d = (int)(&(((struct person *)NULL)->y)); int f = (int)(&(((struct person *)NULL)->x)); int e = (int)((int *)NULL); int g = 0; printf("%d %d %d %d %d/n", a, b, c, d, f); //g = (int)((unsigned long)&(((struct person *)uu)->y)); g = (int)(&(((struct person *)uu)->y)); printf("%d/n", g); return 0; }

 

 

主要是要说 #define OFFSETOF(type, struc) ((size_t) (&((type *) NULL)->struc))

 

的用法，这个可以得到type->struc 对于首地址的偏移。这个不错@@