c++ - 开场流量不好？

Question

当我以二进制模式打开文件时，是否存在 is_open() 为 true 但 good() 为 假 ?

bool ok = false;
std::ifstream stream("test.dat", std::ios::binary)
if (stream.is_open())
{
    ok = stream.good();//Does a situation exist where the result of this is false ?
    stream.close();
}

Answer 1

否:std::ifstream 的双参数构造函数文件打开失败需要设置failbit。

§27.9.1.7[ifstream.cons]/2

explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in);

calls rdbuf()->open(s, mode | ios_base::in). If that function returns a null pointer, calls setstate(failbit).

并且，对于 open()，

§27.9.1.4[filebuf.members]/2

basic_filebuf<charT,traits>* open(const char* s, ios_base::openmode mode);

Returns: this if successful, a null pointer otherwise