[Interest] Simple doubt on file i/o

[Mandeep Sandhu]

On Thu, Jun 27, 2013 at 1:09 PM, Nishant Parashar <nishsites at gmail.com>wrote:

> 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.
>

The only problem here is that if the app unexpectedly quits, then I've lost
this data. As I mentioned earlier, since this data is fetched over the n/w
I'd rather commit it immediately.

Thanks,
-mandeep


>
> 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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>
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