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本帖最后由 kangels 于 2013-3-19 10:23 编辑 1 l0 T& m% O0 U. D, L
9 R; k& z5 }8 N2 \! r- [: A丢失的类型信息/ `0 f3 T7 m" `- O. a5 w
猜测& m' u1 q7 M9 K3 C, ~3 T: J y+ L
指针变量应该存储两方面的信息：地址，类型信息# i' u' }, ~' \; V* M
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实证
! o# o, W0 \* p w- Y2 V, B5 J t用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
) ]+ k. ]$ ^) Y( N' v& q反汇编一段代码来看看; d2 U4 Q$ O: s5 M0 P$ W
实例1：
& {" E. Q) b5 s8 |5 `#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 h P) @8 h Q R& F
; c& W) L" S i( m6 \; ^" U实例2：
* d9 c5 |, Z# j( x& {5 W" P: w#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } 6 \" X0 |" q1 Z" r5 E$ `% w" g
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：+ H" f* Q2 T8 V: M7 e6 g8 Q" z
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } * S0 }' [( D L( r
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 ; F& K0 M% L, Z4 A& U
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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。
6 \! c* O1 X( o: 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。" F- R4 x P- [; _* `; E
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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
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