指針加常數的計算結果

#include <stdio.h>  
struct BBB  
{  
    long num;  
    char *name;  
    short int data;  
    char ha;  
    short ba[5];  
}*p;  

int main()  
{  
    p = 0x1000000;  
    printf(" p+0x200=0x%08x\n", p+0x200);  
    printf(" (Ulong)p+0x200=0x%08x\n", (unsigned long)p+0x200);  
    printf("(char*)p+0x200=0x%08x\n", (char*)p+0x200);  
    printf("(short*)p+0x200=0x%08x\n", (unsigned short*)p+0x200);  
    printf("(int*)p+0x200=0x%08x\n", (unsigned int*)p+0x200);  

    return 0;  
}  

運行結果：
p+0x200=0x01003000
(Ulong)p+0x200=0x01000200
(char*)p+0x200=0x01000200
(short*)p+0x200=0x01000400
(int*)p+0x200=0x01000800

解答：
假設在32位CPU上，
sizeof(long) = 4 bytes
sizeof(char *) = 4 bytes
sizeof(short int) = sizeof(short) = 2 bytes
sizeof(char) = 1 bytes

由於是4字節對齊，
sizeof(struct BBB) = sizeof(*p)
= 4 + 4 + 2 + 1 + 1/補齊/ + 2*5 + 2/補齊/ = 24 bytes (經Dev-C++驗證)

p=0x1000000;
p+0x200=__;
=0x1000000 + 0x200*24

(char*)p+0x200 = 0x1000000 + 0x200 * 1 = 0x01000200
(short*)p+0x200 = 0x1000000 + 0x200 * 2 = 0x01000400
(int*)p+0x200 = 0x1000000 + 0x200 * 4 = 0x01000800

結論：
某一類型的指針 + 一個常數 = 這個常數 * 指針所指區域的大小。