C++中的逻辑运算符&&和||

  • by Weihua 
    • a&&(b=b+2,c=c+3)
    cmp DWORD PTR _a$[ebp], 0
je SHORT $L221
mov eax, DWORD PTR _b$[ebp]
add eax, 2
mov DWORD PTR _b$[ebp], eax
mov ecx, DWORD PTR _c$[ebp]
add ecx, 3
mov DWORD PTR _c$[ebp], ecx
    if(a){b=b+2;c=c+3;}
    cmp DWORD PTR _a$[ebp], 0
je SHORT $L221 ;&&->je
mov eax, DWORD PTR _b$[ebp]
add eax, 2
mov DWORD PTR _b$[ebp], eax
mov ecx, DWORD PTR _c$[ebp]
add ecx, 3
mov DWORD PTR _c$[ebp], ecx
    a||(b=b+2,c=c+3);
    cmp DWORD PTR _a$[ebp], 0
jne SHORT $L221 ;||->jne
mov eax, DWORD PTR _b$[ebp]
add eax, 2
mov DWORD PTR _b$[ebp], eax
mov ecx, DWORD PTR _c$[ebp]
add ecx, 3
mov DWORD PTR _c$[ebp], ecx

    &&,||最终会被翻译成je和jne跳转
    完全等价于if语句,不过当逻辑表达式作为判断条件时

    if(a&&b){}

    会在后面加上test eax,eax作为jmp的依据

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