Re: [問題] 發生 EXCEPTION_DATATYPE_MISALIGNMENT
看板C_and_CPP (C/C++)作者littleshan (我要加入劍道社!)時間14年前 (2012/02/14 22:50)推噓5(5推 0噓 12→)留言17則, 2人參與討論串2/2 (看更多)
首先
char* buffer = new char[1024]; // a big buffer
int* pInt = reinterpret_cast<int*>(buffer);
double* pDouble = reinterpret_cast<double*>(buffer);
*pInt = 10;
*pDouble = 20.0;
這樣做是沒問題的，而且得到標準 (C++ 2003 3.7.3.1p2) 的保證：
The allocation function attempts to allocate the requested amount
of storage...The pointer returned shall be suitably aligned so that
it can be converted to a pointer of any complete object type and
then used to access the object or array in the storage allocated.
但是你不是這樣寫的啊！
你看看你怎麼寫：
int* pInt = reinterpret_cast<int*>(buffer);
*pInt = 10;
pInt++;
double* pDouble = reinterpret_cast<double*>(pInt);
原本的 buffer 保證符合 double alignment
但是你轉成 int* 之後改變了它的值
改變後當然就不一定符合 alignment 了
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