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本帖最后由 kangels 于 2013-3-19 10:23 编辑 ! v2 B1 x3 e9 E g( f2 A% c, R
# ?% [# D+ a" o! U& }/ h丢失的类型信息1 R+ c* w3 X- a
猜测
6 L& g$ j- q- N& A5 {7 i' Y指针变量应该存储两方面的信息：地址，类型信息% s0 ?: l5 X- c7 |0 v
/ D' O7 W; g* q: |' K" E- m! H; a实证% n9 s$ D: E7 y& L+ j& }
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
0 V/ R3 \4 ]4 a3 I! n! s1 h反汇编一段代码来看看) q% z0 X! a6 l" N2 [5 |. g7 ^
实例1：3 d( w# o E/ R2 ]- L8 V
#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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x3 b$ s2 o% N+ K$ E2 A1 ^7 `实例2：
! s) Y, U1 P$ t, e0 E1 ^/ K# o+ J% {+ o#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; }
3 G' a' g. q; M% ]) t# B 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 + A4 v* @1 M7 |: k
9 h% p6 v7 N9 x d- ^/ v; q) {
实例3：
, M8 G [2 x& \0 V f#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
1 w) _+ ?/ ]" H6 ? 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
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8 @/ V: y/ ~/ L# I; H: H3 ?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。, P% ~2 s/ ?( j4 b: `7 u4 q- h
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。0 _# k+ h( {# a3 \
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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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