ATL / WTL / STL

26-Aug-04 2:49

Hi I've basically created a Class called a Session which uses the STL <vector> container to Add 'Jobs objects'. The Job objects add further record objects.

The class as it stands is working fine.

What i want is to write the Session object to a file.
then the next time the app starts i want to read back in the class data from the file.

What i've tried:
1:
I've played with File Mapping, and it seems fine with structures but when i try it with my class using STL, it falls over.
2:
ofstream using the binary flag. - this seems to write it away ok but i have real trouble reading it back in.

Have you had any experience writing a class object to a file that uses the STL? D'Oh! | :doh:

thanks in advance

Carl

Assemblysoft.com

Nitron26-Aug-04 5:04

26-Aug-04 5:04

crandall wrote:
Have you had any experience writing a class object to a file that uses the STL?

What I usually do is overload the << operator and use that to write my class data members to the stream. You can do this for a stream or a CArchive if you're blending in MFC. This way you could just add the object in your Serialize() code or just insert it natively to a stream.

~Nitron.

ññòòïðïðB A start

AssemblySoft26-Aug-04 5:23

26-Aug-04 5:23

1:
If i overloaded the << operator would i be able to achieve something like below?

(might not be completely accurate as just started using fstream rather than fstream.h)

Session s1
s1.DoSomething();
ofstream dataOut(pfileName,ios::binary);
dataOut.write( (char*) &s1,sizeof s1);
dataOut.close();

//On another Day
ifstream fin;
Session *pob;
ifstream fin;
fin.open(pfileName,ios::binary);
fin.read((char*) pob,sizeof(pob));
pob.DoSomething();
fin.close();

2:
With the read in, If the Session contains a vector container of objects of another class, would the sizeof(pob) be correct?

thankyou

Carl

Nitron26-Aug-04 5:28

26-Aug-04 5:28

No, it doesn't work that way. You have to manually store off your data members individually because they are most likely not in a contiguous memory block. If Session was a struct and you were careful of your struct member data alignment, then that could possibly work out OK.

~Nitron.

ññòòïðïðB A start

AssemblySoft26-Aug-04 5:43

26-Aug-04 5:43

Ok i see how i would do that for the Session class, and i just read an article on transient types which need to be converted to basic types first, but how would i go about storing the items in the vector?

do i store each member of each object by looping through with an iterator?

thanks

Carl

Nitron26-Aug-04 5:45

26-Aug-04 5:45

crandall wrote:
do i store each member of each object by looping through with an iterator?

yup.

~Nitron.

ññòòïðïðB A start

AssemblySoft26-Aug-04 5:51

26-Aug-04 5:51

Ok so i can't see why i can't get that bit to work.

How about reading it back in? (please don't just say reverse it)

I create an object of the class
Do i then go through and push_back (re create) from my basic types?
Does that mean i need to store the amount of records for later?

STL was supposed to make my life easier - lol

thanks

Carl

Nitron26-Aug-04 5:54

26-Aug-04 5:54

crandall wrote:
(please don't just say reverse it)

Poke tongue | ;-P

Well, you could either store the number of records as you mentioned, or you could just process until you reach eof(). Have a look at my CDataFile class[^] to see how I do it.

~Nitron.

ññòòïðïðB A start

AssemblySoft26-Aug-04 6:10

26-Aug-04 6:10

thanks a lot for your help Suspicious | :suss:

Todd Smith7-Sep-04 12:18

Todd Smith

7-Sep-04 12:18

I've used this with good success

http://www.codeproject.com/soap/zxmlparser.asp[^]

Todd Smith

AssemblySoft7-Sep-04 23:28