Programming Forums > Application Development > C++

Seif · May 21st, 2006, 9:25 AM

Hi just a quick question. I have a class called person, of which I would like to save to a file. I was wondering if I could save it to a file as I would a struct:

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fin.read((char *)(&newPerson), sizeof(Person));

and to load it again:

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fout.write((char *)(&newPerson), sizeof(Person));

Have tried a couple of times but can't seem to get it to work. Is it actually possible? I really dont want to save attributes of each object on a seperate line if possible.

Cheers in advance.

Seif.

DaWei · May 21st, 2006, 9:46 AM

In C++ a class and a struct are essentially the same thing. The difference is default exposure (public, private, etc.). The problem with saving them to disk is that they might not look like what you think they look like. Compilers tend to align members on "even" boundaries, with the result that there are unused areas of padding. "Even" boundaries depend on the underlying architecture of the machine. Most compilers allow you to tell them not to do this. The saving is bytes, the cost is performance. Even if you get it right it might not work portably. It's what serialization is all about.

Seif · May 21st, 2006, 2:20 PM

Thanks DaWei, I've done a read of object serialization and found exactly what I needed. I knew the similarities of structs and classes but weren't sure if i was possible, and believe it or not my lecturer didn't know either when i asked him

thank god for the PFO!

nnxion · May 21st, 2006, 3:51 PM

Quote:

Originally Posted by Seif

and believe it or not my lecturer didn't know either when i asked him

That should be pretty basic stuff for a lecturer. (I could be wrong, as I'm not.) I always asked questions they didn't know, but as you can imagine, they were on slightly more advanced topics.

DaWei · May 21st, 2006, 3:59 PM

Don't get me started

.

May 21st, 2006, 9:25 AM	#1
Seif Hobbyist Programmer Join Date: Jan 2006 Location: UK Posts: 242 Rep Power: 3	Classes in fstream Hi just a quick question. I have a class called person, of which I would like to save to a file. I was wondering if I could save it to a file as I would a struct: (Toggle Plain Text) fin.read((char )(&newPerson), sizeof(Person)); fin.read((char )(&newPerson), sizeof(Person)); and to load it again: (Toggle Plain Text) fout.write((char )(&newPerson), sizeof(Person)); fout.write((char )(&newPerson), sizeof(Person)); Have tried a couple of times but can't seem to get it to work. Is it actually possible? I really dont want to save attributes of each object on a seperate line if possible. Cheers in advance. Seif.

May 21st, 2006, 9:46 AM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	In C++ a class and a struct are essentially the same thing. The difference is default exposure (public, private, etc.). The problem with saving them to disk is that they might not look like what you think they look like. Compilers tend to align members on "even" boundaries, with the result that there are unused areas of padding. "Even" boundaries depend on the underlying architecture of the machine. Most compilers allow you to tell them not to do this. The saving is bytes, the cost is performance. Even if you get it right it might not work portably. It's what serialization is all about. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

May 21st, 2006, 3:59 PM	#5
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Don't get me started . __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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May 21st, 2006, 2:20 PM	#3
Seif Hobbyist Programmer Join Date: Jan 2006 Location: UK Posts: 242 Rep Power: 3	Thanks DaWei, I've done a read of object serialization and found exactly what I needed. I knew the similarities of structs and classes but weren't sure if i was possible, and believe it or not my lecturer didn't know either when i asked him thank god for the PFO!

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Programming Forums > Application Development > C++

Classes in fstream