473,705 Members | 4,552 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

Re: Deriving from ifstream

On 11 avr, 17:44, "mc" <mc_r...@yahoo. comwrote:
Let me add some reasons to some of the whys. First off, what
I provided is just a small snapshot of a very large file which
parses an old data storage file. I did not include the
documentation with this post as it's north of hundreds of
pages. So the fact the the float is read as an int is very
well detailed in said docs. But that's beyond the point.
OK. If the actual format is well documented, that's half the
battle won already.

Note, however, that reading a float as an int is still very
implementation dependent, since the actual internal format of a
float varies between machines. The documentation should specify
the format of the float in the file, either by reference to some
known format (e.g. IEEE), or by explicitely specifying how the
data is laid out (high bit sign, then 11 bits exposant, in
excess 1023, then mantissa, base 2...---most people just use an
established format).
Then, as I mentioned unclearly, the heart of the problem for
me lies in the constructor: how can I create an le_ifstream
off of an existing ifstream??
In a certain sense, you can't. iostream's aren't copiable.
The usual solution binary I/O is to create a new stream type,
iMyFormatStream , which derives from std::ios (for the error
handling), and define the usual >and << operators on it (but
in a way that they do binary I/O, in your format, and not text
I/O). The basic abstraction of an istream or an ostream is
text, and deriving from it for binary I/O is a potential source
of errors.

All that you use from an existing, open stream, would be the
streambuf. And even then, if the file is pure binary, it's
generally preferable to provide your own derived classes, along
the model of ifstream, and take care of the open yourself. That
way, you can ensure that the filebuf is opened in binary mode,
and that it is imbued with the "C" locale. (Another thing you
have to watch out for---some locales might do code translation.)
The ifstream points to a file opened in binary mode that
actually contains many files stuck one after the other. Each
time a file of a different type is encountered, it's parsed
using an ifstream cast/converted into the relevant derived
class, e.g. le_ifstream. How I read the data is irrelevant.
As long as it is correct. The code you posted had several
serious errors, which would cause it to fail in some specific
cases.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
Jun 27 '08 #1
0 1350

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

2
13774
by: Dave Johnston | last post by:
Hi, I'm currently trying to create a wrapper that uses C functions but behaves like ifstream (from fstream.h) - this is because the platform I'm using (WinCE) doesn't support streams and this is the easiest way to take a huge project across onto it. Basically, I've hit a problem. I have no idea how the ifstream class handles directories. In the code I have (which I didn't write), there are several places whereby an ifstream stream is...
6
3659
by: Herv? LEBAIL | last post by:
Hi everybody, I'm writing a program which use the <string>, <vector> and <ifstream> classes. Given an array of string, i.e vector<string> file_names, example : file_names = "file1.txt" file_names = "file2.txt" etc ...
6
3387
by: Ram Laxman | last post by:
Iam new bie to C++ programming.. I want to write a program which will read the Comma separated values(CSV) file column wise. For example: In a.txt: "TicketNumber","Phone","CarNumber" 10,20,30
28
4096
by: Steven T. Hatton | last post by:
This may be another question having an obvious answer, but I'm not seeing it. I'm trying to create a class that derives from std::valarray<std::string>. I don't need a template, and I haven't come across any examples of a construct like what I show below. Perhapes it's simply a bad idea. If there is something fundamentally wrong with this approach please let me know. Can anybody tell me if there is a way to get the following to work? I...
4
3733
by: hall | last post by:
Hi. I ran across a bug in one of my problems and after spending some time tracking it down i found that the problem arose in a piece of code that essentially did this: ----------- ifstream in("in.txt"); if(!in) {cout << "error\n";} in.close(); if(!in) {cout << "error\n";} in.close(); if(!in) {cout << "error\n";}
10
17981
by: sam | last post by:
Hi, Can anyone tell me how to print a file name from ifstream? the following cout code does not print the filename I created with ifstream preivous: ifstream is; is.open ("text.txt");
15
4083
by: Nindi73 | last post by:
HI If I define the class DoubleMap such that struct DoubleMap : public std::map<std::string, double>{}; Is there any overhead in calling std::map member functions ? Moreover are STL containers destructors virtual >
1
4908
by: Xiaozhou.Yin | last post by:
Hi~ In the program,I first used the ifstream variable fin open the file and,open it again after called the fin.close().But the fin is fieled to open the file in the second time.The book I'm learning hadn't picked out this.Is it a common problem?Or just occurs in Vc++6.0? #include<fstream> #include<iostream> using namespace std; int count(ifstream& fin);
11
8136
by: adramolek | last post by:
So... I'm trying to get used to using C++ ifstream (or ofstream) instead of stdio (although I'm having second thoughts). Anyways, I want to be able to display a meaningful error message if ifstream fails to open a file, but nothing I read about ifstream says anything about a reliable place to get an error message. Using stdio I can simply do: FILE *f = fopen(filename, "rb"); if (!f) perror(filename);
0
8767
marktang
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
0
8689
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
0
9273
Oralloy
by: Oralloy | last post by:
Hello folks, I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>". The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed. This is as boiled down as I can make it. Here is my compilation command: g++-12 -std=c++20 -Wnarrowing bit_field.cpp Here is the code in...
0
9136
jinu1996
by: jinu1996 | last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth. The Art of Business Website Design Your website is...
1
9030
by: Hystou | last post by:
Overview: Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
0
8979
tracyyun
by: tracyyun | last post by:
Dear forum friends, With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
0
7893
agi2029
by: agi2029 | last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own.... Now, this would greatly impact the work of software developers. The idea...
1
3137
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
2
2486
muto222
by: muto222 | last post by:
How can i add a mobile payment intergratation into php mysql website.

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.