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What is the output of the following code?

{int x = 10;int y = 10;x = x++;y = ++y;printf("%d,%d\n",x,y); }

A.10,10

B.10,11

C.11,10

D.11,11

編譯器實際測試結果

GCC : 11,11

VC: 11,11

TCC:10,11

STD C99?

第6.5.16部分第3條

An assignment operator stores a value in the object designated by the left operand. An
assignment expression has the value of the left operand after the assignment, but is not an
lvalue. Thetype of an assignment expression is the type of the left operand unless the
left operand has qualified type, in which case it is the unqualified version of the type of
the left operand. The side effect of updating the stored value of the left operand shall
occur between the previous and the next sequence point.

VC反匯編結果

x = x++;
004113DC ?mov ? ? ? ? eax,dword ptr [x] ?
004113DF ?mov ? ? ? ? dword ptr [x],eax ?
004113E2 ?mov ? ? ? ? ecx,dword ptr [x] ?
004113E5 ?add ? ? ? ? ecx,1 ?
004113E8 ?mov ? ? ? ? dword ptr [x],ecx ?
y = ++y;
004113EB ?mov ? ? ? ? eax,dword ptr [y] ?
004113EE ?add ? ? ? ? eax,1 ?
004113F1 ?mov ? ? ? ? dword ptr [y],eax ?
004113F4 ?mov ? ? ? ? ecx,dword ptr [y] ?
004113F7 ?mov ? ? ? ? dword ptr [y],ecx ?

到現在為止合理的答案是D

不過，如果令

d = （x = x++）;

TCC、VC的輸出，d為10，很費解。

原題

http://www.cnblogs.com/justcxtoworld/archive/2013/04/06/3002719.html

轉載于:https://my.oschina.net/u/269555/blog/121032

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