Specific data extraction from .txt files using fstream.h

**xScen3xHdstyl3x** · 10-26-2011

Hello guys.

I bought a logbook today for my car, and I wondered why the hell not just create a software app for it? :P

I want to store the information and I am obviously going to use fstream.h to handle this I/O, but I am just wondering:
I want the program to be able to update itself on startup with previously entered information (Kinda like a logbook, RIGHT? :P ) and I am not very experienced with the file I/O use.
How would I extract certain lines of information from the text file, and assign it to a variable?
Even just an example to extract and display the starting odometer reading would be appriciated.. I mean, there's no point to this if I have to type in every single thing, especially when certain values will remain the same..

Thanks in advance!

**Elysia** · 10-26-2011

You will be using <fstream>, not <fstream.h>. If you use the later, then it's time to upgrade your compiler.
As for your question, here are two examples:

file >> variable;

This extracts an identifier that can be converted into the type of the variable until the next whitespace character (enter, space, tab).
It can be used to extract a number from a row that looks like "123 456", for example.

std::getline(file, variable);

Reads an entire row from file into variable. Variable must be a std::string.
You can convert the row into some other type by using stringstreams or boost:

T myvar = boost::lexical_cast<T>(variable);

**xScen3xHdstyl3x** · 10-27-2011

I still don't see how that is going to give me the ability to extract specific data from a file? Isn't there some sort of command to extract a line (like... cin.getline(12)) or something?? Totally lost

**phantomotap** · 10-27-2011

O_o

Well, if you were, for example, to get the first line, you'd have line one; do you know what you'd have if you got the next line?

Soma

**Elysia** · 10-28-2011

Originally Posted by xScen3xHdstyl3x

I still don't see how that is going to give me the ability to extract specific data from a file? Isn't there some sort of command to extract a line (like... cin.getline(12)) or something?? Totally lost

I told you how to read a line. What more do you want to know?

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