C++ Permission Control Class

We need a permission control system written in C++. The system will check permissions from a database but we don't need the coder to work with a database. The permissions can be transmitted as if they were from a database using some interface functions, etc... The permission system will be used to provide atomic permissions. Meaning a different permission scheme for every file, item, object, etc... Permissions should be similar to Linux permissions: read, write, execute. There will be specific users and multiple users can be groups and multiple groups can again be groups. Users and groups will have seperate permissions for seperate files/objects. If a permission for a file/object is not explicitly specified than it is the default general permission for the user/group. If a permission is explicitly defined than this will be the current permission for the current user for this file. THe code written should be portable and tested on Windows Vista, Windows 7, 64 bit versions, Linux (Ubuntu for example) and Mac OS X. The code should be compilable as is with gcc and Visual Studio. If different measures must be taken to compile the codes than these should be defined as macros inside the codes. Please let me know if you need more information. After the bidder is selected a SRS document will be provided explaining the concepts and required functionality clearly.