c++ - stringstream 读取失败是不确定的吗？

Question

我有一些代码在不同的编译器上表现不同:

std::string strVal = "11";
std::stringstream stream( strVal );  
auto value = false;

if( !( stream >> std::noboolalpha >> value ) )
{
    // report error - this path is taken on both compilers
}

// "value" is "false" here on in VS 2017, but "true" on GCC 4.6

行为上的差异是预期的，还是 GCC 中的错误？

根据 cppprefence :

If extraction fails (e.g. if a letter was entered where a digit is expected), value is left unmodified and failbit is set.

但是，value 在 GCC 4.6 上被修改为 true。

Answer 1

MSVC 错误。 [facet.num.get.virtuals]/6:

Effects: If (str.flags()&ios_­base​::​boolalpha) == 0 then input proceeds as it would for a long except that if a value is being stored into val, the value is determined according to the following: If the value to be stored is 0 then false is stored. If the value is 1 then true is stored. Otherwise true is stored and ios_­base​::​failbit is assigned to err.