Create file and read text with QFile and QTextStream

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26th May 2009, 14:42
jano_alex_es

Create file and read text with QFile and QTextStream

Hi,

in the docs is written how to read text data from a file, how to write text data to a file... but it does not say how to create a file. It always starts with qfile::open but if we don't have that file we need to create it first. How can we do that?

On the other hand, seems like I just need to add "\n" in the middle of the string associated to QString in order to have different rows, is that true? does it work differently in Windows OS?

thanks!
26th May 2009, 16:22
auba

Re: Create file and read text with QFile and QTextStream

Quote:

Originally Posted by jano_alex_es

but if we don't have that file we need to create it first. How can we do that?

Doc of QFile::open says:

Quote:

Note: In WriteOnly or ReadWrite mode, if the relevant file does not already exist, this function will try to create a new file before opening it.

Quote:

Originally Posted by jano_alex_es

On the other hand, seems like I just need to add "\n" in the middle of the string associated to QString in order to have different rows, is that true? does it work differently in Windows OS?

It works this way: when you only put \n at the end of a line, Notepad on Win32 will not display the text correctly. If you put \r\n at the end, vi will display ^M at the end of each line.
If only QT-Apps use the file, you can use endl and ignore all other editors, else you'll have to replace \r\n or \n to what you want before loading/saving.
26th May 2009, 16:32
fullmetalcoder

Re: Create file and read text with QFile and QTextStream
Quote:

Originally Posted by auba

It works this way: when you only put \n at the end of a line, Notepad on Win32 will not display the text correctly. If you put \r\n at the end, vi will display ^M at the end of each line.
If only QT-Apps use the file, you can use endl and ignore all other editors, else you'll have to replace \r\n or \n to what you want before loading/saving.

Small corrections :
- when opening the device (QFile or any QIODevice) in Text mode, you can just use the LF ('\n') character as it is automatically converted into local line endings (may it be LF, CR or CRLF)
- conversely, when reading a file opened in Text mode local line endings are converted into LF to make it easier to process the content without having to mess with line endings
- this issue is purely independent of Qt, nowadays most applications are able to read files of any line endings (even Wordpad does it)
26th May 2009, 16:59
jano_alex_es

Re: Create file and read text with QFile and QTextStream

Quote:

Doc of QFile:pen says:

My bad! I didn't see that open() overload... I just read the other two :S

thanks!
27th May 2009, 07:26
auba

Re: Create file and read text with QFile and QTextStream

Quote:

Originally Posted by fullmetalcoder

file opened in Text mode local line endings are converted into LF to make it easier to process the content without having to mess with line endings

Cool, that's new to me too, but very useful. Indeed, I did not care about linefeeds since I'm using qt4, so my info was a little bit old :rolleyes:

Quote:

Originally Posted by fullmetalcoder

nowadays most applications are able to read files of any line endings (even Wordpad does it)

if you mean "nowadays" = Vista... most of our customers are still using XP, some of them even w2k :D
27th May 2009, 12:49
fullmetalcoder

Re: Create file and read text with QFile and QTextStream

Quote:

Originally Posted by auba

if you mean "nowadays" = Vista... most of our customers are still using XP, some of them even w2k :D

"Nowadays" is not related to OS but to applications. Wordpad from WinME was already able to deal with LF line endings properly (I did not try CR ones but I guess it should have worked as well) and, honestly, apart from Notepad obviously, I have never EVER encountered a worse/more outdated text editor than Wordpad so it acts as a "lowest common denominator" here.