[Interest] Simple doubt on file i/o

[Nishant Parashar]

Since the data is very less. Read the file once during start-up of app and
prepare the in-memory QMap. This QMap is used for any set/get calls by the
app, don't read/write to file. Finally when we exit the app, write the QMap
to file wiping out old contents.

On 27 June 2013 12:26, Mandeep Sandhu <mandeepsandhu.chd at gmail.com> wrote:

> Hi,
>
> I wanted to know if I'm doing file i/o the right way in one of my apps.
>
>  I'm writing  a small helper class for one of my applications which is
> supposed to store data, in the form of key-value pairs, in a file. This is
> very similar to QSettings but w/o any fancy groups/sections that it
> provides. So lets assume that I have to use a file based approach only! :)
>
> It provides 2 functions - get(key) and a set(key, value) and they behave
> exactly like QMaps equivalent functions, i.e if the key exists, it'll
> overwrite the value, else it'll add a new entry. This class takes either a
> filename as input or a QFile itself.
>
> Assumptions:There won't be much data written to the file (max 1-2 KB). The
> set function will not be called very often (probably once or twice in the
> lifetime of the app). The get fxn will be called a little more often.
>
> Here's what I do in the 2 functions (skipping error condition checks keep
> it simple):
>
> get(key):
> * Open the file in Read-Only mode.
> * Parse the data and prepare a QMap of the key-value pairs.
> * Close the file
> * Return the value for the key
>
> set(key, value):
> * Open the file in Read-Only mode.
> * Parse the data and prepare a QMap of the key-value pairs.
> * Close the file
> * Open the file in Write-Only & Truncate mode
> * Insert the new key-value in the map
> * Write the map
> * Close the file
>
> In the set function I'm opening the file twice - once to read it's content
> and prepare the map and next I open it in truncate mode as I want to wipe
> off the existing data and write the new data afresh.
>
> Is there a simpler way to achieve what I'm doing with a file? I'm assuming
> the 2 open-close calls in set() are ok as it won't be called very often.
>
> Thoughts?
>
> Thanks,
> -mandeep
>
>
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