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有关C语言运算符优先级和结合律的思考

2012-09-21 15:45 225 查看
(1) b=*p++;

(2)b=(*p)++;

(3)b=++*p;

(4)b=++(*p);

(5)b=*++p;

(6)b=*(++p);

上面6式子,哪些是等价的?

反汇编代码:

b=*p++;
00411BD9  mov         eax,dword ptr [p] 
00411BDC  mov         ecx,dword ptr [eax] 
00411BDE  mov         dword ptr [b],ecx 
00411BE1  mov         edx,dword ptr [p] 
00411BE4  add         edx,4 
00411BE7  mov         dword ptr [p],edx 
    b=(*p)++;
00411BEA  mov         eax,dword ptr [p] 
00411BED  mov         ecx,dword ptr [eax] 
00411BEF  mov         dword ptr [b],ecx 
00411BF2  mov         edx,dword ptr [p] 
00411BF5  mov         eax,dword ptr [edx] 
00411BF7  add         eax,1 
00411BFA  mov         ecx,dword ptr [p] 
00411BFD  mov         dword ptr [ecx],eax 
    b=++*p;
00411BFF  mov         eax,dword ptr [p] 
00411C02  mov         ecx,dword ptr [eax] 
00411C04  add         ecx,1 
00411C07  mov         edx,dword ptr [p] 
00411C0A  mov         dword ptr [edx],ecx 
00411C0C  mov         eax,dword ptr [p] 
00411C0F  mov         ecx,dword ptr [eax] 
00411C11  mov         dword ptr [b],ecx 
    b=++(*p);
00411C14  mov         eax,dword ptr [p] 
00411C17  mov         ecx,dword ptr [eax] 
00411C19  add         ecx,1 
00411C1C  mov         edx,dword ptr [p] 
00411C1F  mov         dword ptr [edx],ecx 
00411C21  mov         eax,dword ptr [p] 
00411C24  mov         ecx,dword ptr [eax] 
00411C26  mov         dword ptr [b],ecx 
    b=*++p;
00411C29  mov         eax,dword ptr [p] 
00411C2C  add         eax,4 
00411C2F  mov         dword ptr [p],eax 
00411C32  mov         ecx,dword ptr [p] 
00411C35  mov         edx,dword ptr [ecx] 
00411C37  mov         dword ptr [b],edx 
    b=*(++p);
00411C3A  mov         eax,dword ptr [p] 
00411C3D  add         eax,4 
00411C40  mov         dword ptr [p],eax 
00411C43  mov         ecx,dword ptr [p] 
00411C46  mov         edx,dword ptr [ecx] 
00411C48  mov         dword ptr [b],edx
答案:(3)=(4),(5)=(6)
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