1：iostate rdstate ( ) const; 返回的是iostate,簡(jiǎn)單的說也就是一個(gè)int數(shù)值.用2進(jìn)制數(shù)據(jù)的某一個(gè)位置設(shè)置為1表示一種狀態(tài)

2：failbit 的定義如下，二進(jìn)制數(shù)據(jù)的第二位為1的時(shí)候說明是該數(shù)據(jù)。

static const _Iostate goodbit = (_Iostate)0x0; static const _Iostate eofbit = (_Iostate)0x1; static const _Iostate failbit = (_Iostate)0x2; static const _Iostate badbit = (_Iostate)0x4; static const _Iostate _Hardfail = (_Iostate)0x10;

3：input.rdstate() & std::ios::failbit  通過位運(yùn)算的與來判斷當(dāng)前的狀態(tài)是否是failbit。