c++ - stringstream.rdbuf causing cout to fail -


i surprised see program go quiet when added cout @ point, isolated responsible code:

std::stringstream data; data<<"hello world\n"; std:std::fstream file{"hello.txt", std::fstream::out}; file<<data.rdbuf(); std::cout<<"now rdbuf..."<<std::endl; std::cout<<data.rdbuf()<<std::endl; std::cout<<"rdbuf done."<< std::endl;

the program quietly exits without final cout. going on? if change last .rdbuf() .str() instead completes.

during call std::cout<<data.rdbuf(), std::cout unable read characters data's filebuf because read position @ end of file after previous output; accordingly, sets failbit on std::cout, , until state cleared further output fail (i.e. final line ignored).

std::cout<<data.str()<<std::endl; not cause cout enter failed state because data.str() returns copy of underlying string regardless of read position (for mixed-mode stringstreams anyway).


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