Hello , I am very new in boost file system and simply I wrote a sample to use boost file system. I need a file descriptor for both read and write. When I implement below code for "sink" and "source" files, they work. But I don't understand why I couldn't open a basic_file object to read and write. Any comment is appreciated. Thanks in advance. void test_boost2(){ long long size=5*1024*1024; char buffer [L_tmpnam]; const char* prefix = "c1t"; string tempPath(archive::tmpdir()); filesystem::path path(tempPath); filesystem::space_info spi(space(path)); strcpy(buffer,prefix); if( spi.free > size * 3/2 && tmpnam (buffer+sizeof(prefix)-1) != NULL){ buffer[sizeof(prefix)-1]='_'; path/=buffer; boost::iostreams::basic_file<char> *tmpFile= new basic_file<char>(path.string()); tmpFile->open(path.string()); if(tmpFile->is_open()){ long long p=size-DATA_SIZE-2; tmpFile->seek(p,ios_base::beg); tmpFile->close(); } delete tmpFile; } }