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本帖最后由 kangels 于 2013-3-19 10:23 编辑 % A. B& j! o! {& v
, F) W7 P' z6 o" E; [丢失的类型信息- [" V3 {" M) Y# U/ r% Z
猜测, _. d( G# r8 B$ C* r
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; ~- u: ^" a0 h& P% m" 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
6 T4 r7 Y0 a* Y2 }* m" d反汇编一段代码来看看
! Q* z9 P0 n- Y N/ _/ c实例1: g; o$ {" C5 \' M M5 n2 o: S8 i8 u
#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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: D0 r* u$ B" I实例2:& q! G6 |) E8 W" \: d. a, b, ?: D7 t
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } ) |6 @, `9 G$ k4 e. N! V6 z, e
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 9 d6 p' d6 @% N0 E
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实例3:& `2 z% ~/ h9 m; Q/ y( Q, k
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
$ }# A' F4 @0 R+ F4 Z 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 & M) S! S1 v" l6 R
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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。
+ l! C9 S _1 v% r: m0 Y& o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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