#iostreams
4 posts tagged #iostreams.
std::endl is a hidden flush, and clang-tidy flags it
std::endl is not a fancy newline; it is a newline plus a flush, and the flush is what costs you. A flush-counting streambuf proves that a newline flushes zero times and std::endl flushes every time. When to want the flush (crash-survivable logs), when not, and why clang-tidy flags it. Episode 7 of the concurrent I/O series.
std::print does not tear the way std::cout does
The fixes so far needed cooperation or a lock. C++23's std::print gives per-call atomicity for free: a single print call never interleaves with another, the way printf never did and std::cout always could. But the guarantee is per-call, so a line split across two calls can still tear. Episode 4 of the concurrent I/O series.
std::osyncstream makes concurrent output atomic
std::cout garbled its own output across threads. C++20's std::osyncstream fixes it: each thread buffers a line privately and emits it to the stream atomically on destruction. One wrapper, whole lines, with one sharp edge: the guarantee holds only if every writer uses it. Episode 2 of the concurrent I/O series.
Your std::cout logging has no data race and still tears
Qt's message-handler contract says the handler must be reentrant: called from many threads at once. Point it at std::cout and the output tears, even though the C++ standard guarantees no data race. 'No data race' and 'no interleaving' are different promises, and this series closes the gap. Episode 1 of the concurrent I/O series.