replace_extension seems to have the wrong behaviour if the provided new extension does not start with a dot. The following program: #include <iostream> #include <boost/filesystem.hpp> int main() { boost::filesystem::path p("foo.bar"); std::cout<<p<<'\n'; p.replace_extension("foo"); std::cout<<p<<'\n'; return 0; } built with the following command line on linux 64 (with boost 1.48.0): $ g++-4.6.2 -DBOOST_DISABLE_ASSERTS -DBOOST_FILESYSTEM_VERSION=3 -DBOOST_FILESYSTEM_NO_DEPRECATED -o toto -I/soft/bal/usr/gcc-release/boost/include toto.cc -L/soft/bal/usr/gcc-release/boost/lib -lboost_filesystem -lboost_system produces the following output: "foo.bar" "foo" but should produce: "foo.bar" "foo.foo" as read from the documentation path& replace_extension(const path& new_extension = path()); Postcondition: extension() == replacement, where replacement is new_extension if new_extension.empty() || new_extension[0] == the dot character, otherwise replacement is the dot character followed by new_extension. Adding the dot before foo makes the program work: p.replace_extension(".foo"); This seemed to work with filesystem v2. Frédéric Bron