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本帖最后由 kangels 于 2013-3-19 10:23 编辑 0 l0 p5 Z0 l% K* G( w9 U
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丢失的类型信息- ]# r% O, [8 C' w( V, X
猜测! e. z o5 ?+ j+ f5 x" Y
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) B( h1 Y! S( x+ g
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
% T' R' F* N/ F% J% _) C* \反汇编一段代码来看看
8 `* Z1 t3 b4 z& Y |实例1：: F9 ]5 ^) N# c$ p. e% I
#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 $ x$ |5 `/ `7 I: Q' u
9 ~' R0 ?( x, u# f8 a8 k( n& ]2 `实例2：7 d; `; S y; d% E9 d
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; }
0 `6 a/ W& h0 Z2 O" I 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 6 {3 M7 m; j: _. p4 V4 e
5 x0 y* G. L- L5 r; c" @# Z+ ~实例3：
6 K: C; `8 ?9 v% J#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } ) s/ P6 ]* Z/ k! ~; ^- ^- Z: E- k
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 + P6 n$ a# Y; x4 x' U1 p/ H }
% n7 P8 Q; Y9 O6 [5 x* m8 [9 y. 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。' p1 {+ T0 C# K$ E$ a. G e1 U
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。
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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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