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Jul 24th, 2004
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fstream and struct question

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Hi !

I would like to ask your help. Since days, I am reading fstream tutorial in tutorials section as I am trying to put together 3routines:

1., Can write a structure to a file. (ButtonClick1)
2., Can tell how many records in the file (ButtonClick2)
3, Can read back the structure from the file. (ButtonClick3)

I thought is simple but I can not get it to work.

- I mean I had created the structure in the main header like this :

private: // User declarations
struct WebSites
{
AnsiString name;
int level;
int image_index;
int selected_index;
};

- And the 3 routines to read and write struct to files :

//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
WebSites p_Data;

p_Data.name = Edit1->Text;
p_Data.level = StrToInt(Edit2->Text);
p_Data.image_index = StrToInt(Edit3->Text);;
p_Data.selected_index = StrToInt(Edit4->Text);;

fstream binary_file("c:\\test.dat",ios::out|ios::text|ios::app);
binary_file.write(reinterpret_cast<char *>(&p_Data),sizeof(WebSites));
binary_file.close();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button2Click(TObject *Sender)
{
WebSites p_Data;
int fl_sz;
int total_no_rec;

fstream binary_file("c:\\test.dat",ios::text|ios::in);
binary_file.seekg(0,ios::end);
fl_sz = binary_file.tellg();
total_no_rec = fl_sz/sizeof(WebSites);
Memo1->Lines->Add(total_no_rec);
binary_file.close();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button3Click(TObject *Sender)
{
WebSites p_Data;

fstream binary_file("c:\\test.dat",ios::text|ios::in);
binary_file.read(reinterpret_cast<char *>(&p_Data),sizeof(WebSites));
Memo1->Lines->Add(p_Data.name);
binary_file.close();
}
//---------------------------------------------------------------------------

But it is not working consequently. I mean several times cause general error
fault, or not reading the file or it seems the data written is not even
correct.

So I am completely lost. Could somebody help me please ?

Many thanks in advance,

Moore
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Newbie Poster
coolice is offline Offline
9 posts
since Jul 2004
Jul 24th, 2004
0

Re: fstream and struct question

Using Standard C++ (98),eh?,Well the tut was in old C++ and I am still learning STL and the new C++ freatures.

reinterpret_cast<char *>(&p_Data): I belive this is the problem area.
Try:reinterpret_cast<char *>(p_Data)

I am not too sure :-| ,so you can even try static_cast<char *>.I really havent got around to using this yet.Better stick to (char*)&p_Data.
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FireNet is offline Offline
256 posts
since May 2004
Jul 24th, 2004
0

Re: fstream and struct question

Hi !

I had tried, but honestly, I belive that I had trouble because in is not so wise to use AnsiString in a struct. I have no ide.

BUT !

I had started from the begginning, and I had reconstruct the code. I post here a working version, which also include a little bit of TreeView manipulation, but the main point, that the struct save and load operating perfectly.

BTW : Can I count on the fact that in any windows environment, the absolute maxium for a file or directory name length can not exceed 256 ?

Finnaly, MANY THANKS for that great tutorial, because this version is also built on that.

The code:
//---------------------------------------------------------------------------
void __fastcall Tmain_form::Button1Click(TObject *Sender)
{
struct DataStruct
{
char name[257];
int level;
int image_index;
int selected_index;
};

DataStruct item_data;
TTreeNode * current_item;
ofstream data_file;

data_file.open("c:\\saved.dat", ios::binary | ios::trunc);

for ( int a = 0; a < main_form->main_tree->Items->Count; a++ )
{
current_item = main_form->main_tree->Items->Item[a];

strcpy(item_data.name, current_item->Text.c_str());
item_data.level = current_item->Level;
item_data.image_index = current_item->ImageIndex;
item_data.selected_index = current_item->SelectedIndex;

data_file.write((unsigned char*)&item_data , sizeof(DataStruct));
}

data_file.close();
}
//---------------------------------------------------------------------------
void __fastcall Tmain_form::Button2Click(TObject *Sender)
{
main_form->main_tree->Items->Clear();
}
//---------------------------------------------------------------------------
void __fastcall Tmain_form::Button3Click(TObject *Sender)
{
struct DataStruct
{
char name[257];
int level;
int image_index;
int selected_index;
};

DataStruct item_data;

int total_size;
int total_nr_items;

ifstream data_file("c:\\saved.dat",ios::binary | ios::in);

data_file.seekg(0 , ios::end);
total_size = data_file.tellg();
total_nr_items = total_size / sizeof(DataStruct);

for (int a = 0; a < total_nr_items; a++)
{
data_file.seekg(a * sizeof(DataStruct),ios::beg);
data_file.read((char*)&item_data , sizeof(DataStruct));

Memo1->Lines->Add(item_data.name);
}

data_file.close();
}
//---------------------------------------------------------------------------

Moore
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Newbie Poster
coolice is offline Offline
9 posts
since Jul 2004
Jul 25th, 2004
0

Re: fstream and struct question

You are most welcome.I dont know the exactly if there is any directory path size limit but you can be quite sure the almost no one will use a path which is more than a 100 bytes.It's too long.
Reputation Points: 108
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Posting Whiz in Training
FireNet is offline Offline
256 posts
since May 2004
Jul 25th, 2004
0

Re: fstream and struct question

Quote originally posted by coolice ...
BTW : Can I count on the fact that in any windows environment, the absolute maxium for a file or directory name length can not exceed 256 ?
I might choose to use the standard macro FILENAME_MAX.
Team Colleague
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long time no c
Dave Sinkula is offline Offline
4,790 posts
since Apr 2004

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.
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