Hi, another problems in the same file. A) problem of align because mmap() requires: 1. offset should be a multiple of page size 2. the address start must be a multiple of page size. we have to align the offset and start to page size. for code snip begin from line 444, ===================================== if(address){ address = static_cast<const char*>(address) - m_extra_offset; } ===================================== you make a wrong alignment for address. for example construct a mapped_region object with offset=1 and address=0x3f000002. m_extra_offset is 1, and calculated address is 0x3f000001 which is not page size aligned. another member variable have to imported to record the offset of address and m_base. B) problem of m_size under windows in some case, the m_size is zero (0) under windows. code snipp begin at line 327 (mapped_region::flush) ===================================== if(numbytes == 0) { numbytes = m_size - offset; } ===================================== if m_size is 0, numbytes is a negative. for the problem A, I do suggest m_base/m_offset is the real value not adjusted value. then we just adjust this value in get_size()/get_address()/get_offset() like this: get_size() { if(m_size == 0) return m_size; return m_size - m_extra_offset; } get_address() { return static_cast<char* >(m_base) + m_extra_offset; } get_offset() { return m_offset + m_extra_offset; } Best Regards, Wilbur Lang