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本帖最后由 kangels 于 2013-3-19 10:23 编辑 ) U5 B: ^" X9 J% m: {' ]3 l2 U
1 y5 k, V* U+ Q$ v8 ]1 N丢失的类型信息$ ]3 K8 R$ x. m! b& T! z3 P2 d5 Z* s
猜测
Y6 p& U' V6 t* ~* R. u) Y指针变量应该存储两方面的信息:地址,类型信息6 I7 x" f8 E8 o
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实证
1 ?% f G) q4 r8 a6 i+ ]! D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 U; y% x u# D反汇编一段代码来看看
7 |! f6 }! M. B3 Y& R实例1:( n+ x5 R+ T/ g( K
#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 ' g8 W* O' N, t9 U+ k7 X. E
: ~, Z6 T; l2 D* r实例2:
6 ], Z" S, Q9 M6 ^2 V8 h0 C8 V4 g#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; }
# `/ m6 w2 @* ` 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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4 v/ ` r1 \0 g9 Q实例3:8 R0 @+ [' P1 X1 \+ G. O
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } 7 ` K q" X0 Y9 \& U
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 & D" \3 n4 L3 k. x2 O6 e
$ l( ^' m; [. s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。 p0 G! ~8 b) m V# z; K- ]$ y
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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