Writing a map into file

dpreznik · #1 16-Sep-2009, 12:17

Maybe somebody could please help me understand why I fail to write stl's map of vectors into a file using CFile::Write()?

CPP / C++ / C Code:

typedef std::vector<CLocation> LocationArray;
typedef std::map<int, LocationArray > MapLocationArray;

CPP / C++ / C Code:

		int iSize = sizeof(m_mapLocations);
		cf->Write(&iSize, sizeof(iSize));
		cf->Write(&m_mapLocations, iSize);

When I am writing, the m_mapLocations contains valid data. But when I read from file, it is empty, though the iSize is correct...

CPP / C++ / C Code:

		int iSize = 0;
		cf->Read(&iSize, sizeof(iSize));
		if(iSize > 0)
			cf->Read(&m_mapLocations, iSize);

davekw7x · #2 16-Sep-2009, 13:59

Quote:

Originally Posted by dpreznik

Maybe somebody could please help me understand

The sizeof() operator tells something about the (implementation-dependent) amount of memory used to store information about an object. The value of a C++ sizeof() operation is constant and is determined at compile time.

It's probably the size of a couple of pointers, and the pointers point to "some place" in memory where the actual elements values are stored. You will have to access and store all of the elements individually to be able to save them in a file (they are not necessarily in contiguous memory as far as I can tell).

Regards,

Dave

dpreznik · #3 17-Sep-2009, 05:09

Thank you Dave. This is what I suspected, too. I will store all elements separately, as you say.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Rate This Thread
Rate This Thread:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Airport Log program using 3D linked List : problem reading from file	batrsau	C Programming Language	11	29-Feb-2008 07:44
After execution - Error cannot locate /Skin File?	WSCH	C++ Forum	1	05-Mar-2005 20:03
CD burner wont burn!!	robertli55	Computer Hardware Forum	1	18-Jun-2004 10:53
Yet another CD burner problem: Lite-On LSC-24082K	Erwin	Computer Hardware Forum	1	22-May-2004 11:28
CD Buring Failed	skanth2000	Computer Hardware Forum	1	15-Nov-2003 03:52

Writing a map into file

Re: Writing a map into file

Re: Writing a map into file