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本帖最后由 kangels 于 2013-3-19 10:23 编辑 , Y5 ~+ M" C/ ?7 A f% G$ h4 Z* E! o
4 Y1 F; _ N! x. p: @ o丢失的类型信息+ O! C$ S0 o" |' t* Z: d- T. @
猜测
) J0 y( H/ x+ }% d, {, ~0 M8 q3 N7 Z指针变量应该存储两方面的信息：地址，类型信息
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实证3 V' v7 F; y& ^; N* S+ N
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
9 w4 b( _3 j3 h9 _反汇编一段代码来看看+ L$ R' Q! ~- K7 I' N
实例1：
/ _* D3 ?' v" r#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
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实例2：* V/ { h. b4 s: U5 }% r% _# ^2 \4 x
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } & \+ @: F7 q1 n7 F8 B0 F8 d
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
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实例3：
" b) f' V0 P5 x2 B# U) o' ~#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
9 U# Y! e) }7 ? 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 . H; ]+ d# q3 T$ y+ p/ r7 A. j
3 X1 H7 F4 P: r+ {9 F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。" K5 t' |. [" h6 l L% E
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。: n6 u5 q/ d- k8 |' d
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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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