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Full Discussion: Storing C++-struct in file - problem when adding new item in struct
Top Forums Programming Storing C++-struct in file - problem when adding new item in struct Post 302569813 by DreamWarrior on Tuesday 1st of November 2011 03:51:29 PM
Old 11-01-2011
Agreed with Corona, and I was going to make the same statement, but not seeing the rest of the code, and under the assumption it works, I figured maybe it was memory mapping the file to some fixed address location. That'd allow the pointer values to be stored and actually work so long as they only pointed to an address within the memory mapped region.

That said, I have no idea if the code is actually doing this. And, I must admit, for a properties file it's fetched.

As for the OP, I think you're generally misguided regarding what the code is doing. That struct is unlikely to be stored directly in the file. I'd dig a little deeper in the code and figure out what is reading and writing the file's data.

Better, why don't you just post what the file looks like; with that information we could probably immediately tell you whether or not that exact structure is stored verbatim in the file.
 

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LEARN ABOUT HPUX

iomap

iomap(7)						 Miscellaneous Information Manual						  iomap(7)

NAME

       iomap - physical I/O address mapping

SYNOPSIS

DESCRIPTION

       The mechanism allows the mapping (thus direct access) of physical I/O addresses into the user process address space.  For PA-RISC machines,
       the physical I/O address space begins at and extends to

       The special (device) files for devices are character special files using the dynamic major number allocation scheme.

       The minor number for devices is of the form:

       The physical I/O address is formed by prefixing 0xAAAA with 0xF, and by appending 0x000 (this forces the I/O address to	be  page-aligned).
       The  size  of  the region to be mapped is given by the expression M*(2^S) 4K pages.  For example, the minor number for a device starting at
       that occupies 64MB is

       The driver must be explicitly added to the file, the kernel rebuilt, and the system subsequently rebooted prior to first using

       I/O space is always mapped with both read and write access rights, regardless of the actual permissions on the device special file.

       Multiple processes can have concurrently a single device opened and mapped.  It is the responsibility of the processes to synchronize their
       access.

       Successive calls to to map the same I/O space must be identical to the first mapping.  Identical mappings have the same address and size.

       Note that a process can additionally share I/O space (mapped by with a kernel driver.  However, this is only possible if the driver maps in
       the I/O space with user read/write access rights using the appropriate driver I/O mapping services.  Any I/O space mapped by  drivers  with
       kernel read/write access rights cannot be concurrently mapped by processes using

       No or system calls are supported by the driver.

       The function is used to control the device.  The following requests are defined in

	      Map the	      device  into  user address space at the location specified by the pointer to which the third argument to points.	If
			      the argument points to a variable containing a null pointer,  the  system  selects  an  appropriate  address.   then
			      returns  the  user  address  where the device was mapped, storing it at the address pointed to by the third argument
			      (see below).  Multiple processes can concurrently have the same device mapped.

	      Unmap the       device from the user address space.

       shuts down the file descriptor associated with the device.  If the close is for the last system wide open on the device, the device is also
       unmapped from the user address space; otherwise it is left mapped into the user address space (see above).

WARNINGS

       Be extremely careful when creating and using devices.  Inappropriate accesses to I/O devices or RAM can result in a system crash.

ERRORS

       The address field was out of range,
		      or the request was invalid.

       Not enough memory could be allocated for the mapping.

       Device was already mapped and this mapping was not identical
		      to the initial mapping (same address, size and access rights).

       Read and write calls are unsupported.

       No such device at the address specified by the minor number.

       Required resources for mapping could not be allocated.

       Inappropriate  request for this device type; fildes is not a file descriptor for an device file.

EXAMPLES

       Consider the following code fragment:

		   ...
		   ...

       where is an open file descriptor for the device special file and is the address originally requested by the program.

       If is a null pointer, the system selects a suitable address then returns the selected address in addr.

       If  the	value  in addr is not a null pointer, it is used as a specified address for allocating memory.	If the specified address cannot be
       used, an error is returned (see

SEE ALSO

       mknod(1M).

								     OBSOLETED								  iomap(7)
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