Read from the file twice

luminski

Hi,

i try to do the following

open a file and read only the first line (which is a piece of information i need for something else), then read the whole content and do something with it (actually need to create a QBuffer but i left it out in the snippet below).

i had a look around and put together the snippet below which works. But to achieve the task i open the file, close it and then re-open it again. So just wondering if there's a more graceful way to do it.

QString pathToSomeFile = "/path/to/some/file";

QFile someFile(pathToSomeFile);
if(!someFile.open(QIODevice::ReadOnly)) return;

QTextStream in(&someFile);
QString firstLine = in.readLine();
// do sth with firstLine;

// below i re-open the file as otherwise the content read is blank
someFile.close();
if(!someFile.open(QIODevice::ReadOnly)) return;

QByteArray dataFile = someFile.readAll();
QString wholeContent = QString(dataFile);
// use  QByteArray to create a QBuffer and do more stuff

Thanks

SGaist

Hi,

You can seek back to 0.

Kent-Dorfman

@luminski said in Read from the file twice:

So just wondering if there's a more graceful way to do it.

Are you sure you need a feeform text file? fixed block IO on binary files is much easier to correctly program for.

JonB

@luminski
As @SGaist has said, if you really need to re-read an already-opened-and-partially-read file you can seek(0) to accomplish that.

Alternatively: if the two reading segments of code are "close together", as per the code the show, you could: reverse the order of your operations, read the whole file first and get the first line from what you already read into memory instead of in.readLine(), like:

if(!someFile.open(QIODevice::ReadOnly)) return;

QByteArray dataFile = someFile.readAll();
QString wholeContent = QString(dataFile);
someFile.close();

QString firstLine = wholeContent.split("\n").at(0);