Hello, boost::iostream's documentation says when we write a device, we are allowed to throw in the read() or write() function to report an error. But unfortunately when I do that, it looks like the exception is caught silently, and -1 is returned. I couldn't find where that was done in boost::iostream (the only exception silently caught are when you .close() the stream). I'm starting to suspect it's mingw that does it or something. Here attached is a testcase to reproduce the problem, here's the output I get : C:\Dev-Cpp\Projects\test>g++ foo.cpp -o foo C:\Dev-Cpp\Projects\test>foo.exe testing streambuf_test... works ! testing boost::iostream... failed ! Thank you for your help. Philippe