Writing a map into file

dpreznik · #1 16-Sep-2009, 13:17

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, 14:59

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, 06:09

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

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Writing a map into file

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