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本帖最后由 kangels 于 2013-3-19 10:23 编辑 ! m! [1 U! ~0 z) ] Q) P, E# I
- o/ z! M6 U6 I* f1 }8 S丢失的类型信息
+ S7 u* P" X! E( z4 v猜测
( v* Z: m) n9 T指针变量应该存储两方面的信息：地址，类型信息
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/ ? @9 _2 b% `. n实证 Z9 g+ I$ S6 ]; s4 x- F
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
: e3 K% M y) x反汇编一段代码来看看. e* C( T* ^6 b# |2 ]; K& J: r
实例1：
' B+ a: R6 L; {% V( B5 B% m#include <stdio.h> int gi; int * pi; void main(int argc, char **argv) { pi = &gi; *pi = 12; } 1: #include <stdio.h> 2: int gi; 3: int * pi; 4: void main(int argc, char **argv) 5: { 00411370 push ebp 00411371 mov ebp,esp 00411373 sub esp,0C0h 00411379 push ebx 0041137A push esi 0041137B push edi 0041137C lea edi,[ebp+FFFFFF40h] 00411382 mov ecx,30h 00411387 mov eax,0CCCCCCCCh 0041138C rep stos dword ptr es:[edi] 6: pi = &gi; 0041138E mov dword ptr ds:[00417140h],417144h 7: *pi = 12; 00411398 mov eax,dword ptr ds:[00417140h] 0041139D mov dword ptr [eax],0Ch 8: } 004113A3 xor eax,eax 004113A5 pop edi 004113A6 pop esi 004113A7 pop ebx 004113A8 mov esp,ebp 004113AA pop ebp 004113AB ret 7 O/ F, a- C4 j8 [: [6 C
8 M9 N% \& B C: O& U# G# m: y7 ?# V实例2：$ ?: \" y, J5 p q' L( L
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; }
% u+ d& b, S, J0 y 1: #include <stdio.h> 2: short gs; 3: short * ps; 4: void main(int argc, char **argv) 5: { 00411370 push ebp 00411371 mov ebp,esp 00411373 sub esp,0C0h 00411379 push ebx 0041137A push esi 0041137B push edi 0041137C lea edi,[ebp+FFFFFF40h] 00411382 mov ecx,30h 00411387 mov eax,0CCCCCCCCh 0041138C rep stos dword ptr es:[edi] 6: ps = &gs; 0041138E mov dword ptr ds:[00417140h],417144h 7: *ps = 12; 00411398 mov eax,0Ch 0041139D mov ecx,dword ptr ds:[00417140h] 004113A3 mov word ptr [ecx],ax 8: } 004113A6 xor eax,eax 004113A8 pop edi 004113A9 pop esi 004113AA pop ebx 004113AB mov esp,ebp 004113AD pop ebp 004113AE ret + L$ l: M! w$ J
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实例3：
: g8 Y2 }8 X8 ]$ M#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } 8 L; j$ Q) z2 {3 A/ G8 t
1: #include <stdio.h> 2: char gc; 3: char * pc; 4: void main(int argc, char **argv) 5: { 00411370 push ebp 00411371 mov ebp,esp 00411373 sub esp,0C0h 00411379 push ebx 0041137A push esi 0041137B push edi 0041137C lea edi,[ebp+FFFFFF40h] 00411382 mov ecx,30h 00411387 mov eax,0CCCCCCCCh 0041138C rep stos dword ptr es:[edi] 6: pc = &gc; 0041138E mov dword ptr ds:[00417140h],417144h 7: *pc = 12; 00411398 mov eax,dword ptr ds:[00417140h] 0041139D mov byte ptr [eax],0Ch 8: } 004113A0 xor eax,eax 004113A2 pop edi 004113A3 pop esi 004113A4 pop ebx 004113A5 mov esp,ebp 004113A7 pop ebp 004113A8 ret ) r: p' C3 s2 A/ D
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可以看出指针的类型信息决定了赋值/读取时读/写多少个字节。7 c- z2 b- W. r
读/写多少字节的信息不是存放在指针变量中，而是放到了与该地址相关的赋值指令中。2 C4 v" d7 r: z# V' d
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狗仔卡
发表于 2013-3-12 20:59:39
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貌似很高深的反汇编
楼主
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