Find last of... and write above.

AlvaroS

Hello to everyone.
First of all thanks a lot for reading this post and being able to help.

I have a .txt, for example:

1. Hello world
2. This world is really big...
3. I love this world.

What I would like is to write a line above the last line which contains "world.
So in this case image that I want to write the line "This forum is amazing".
So the .txt will have to be:

1. Hello world
2. This world is really big...
3. This forum is amazing
4. I love this world.

So I have to:
1º first find last word of world.
2º Write above.

How can I do that?
Any help?

thanks a lot!

raven-worx

@AlvaroS

QFile file(fileName);
if (file.open(QIODevice::ReadWrite | QIODevice::Text))
{
    // read lines
    QStringList lines;
    int lastIdx = -1;
    QTextStream in(&file);
    for( int i= 0; !in.atEnd(), ++i )
    {
        QString line = in.readLine();
        lines << line;
        if( line.contains("XXX") )
            lastIdx = i;
    }

    // insert your line
    lines.insert( lastIdx-1, ... );
    
    //write back to file
    file.seek(0);
    file.write( lines.join("\n") );
    
    file.close();
}

You should only use this code if the files aren't too big, since everything is loaded into the memory.
Also i left out some error checking and it's untested, but it should give you an idea.

Chris Kawa

Here's a little shorter version, with a lot less allocations:

//insert stuff before line with last occurrence
void isblwlo(const QString& file, const QString& what, const QString& stuff)
{
    QFile f(file);
    if (!f.open(QIODevice::ReadWrite | QIODevice::Text))
        return;

    QByteArray buff = f.readAll();
    int pos = buff.lastIndexOf(what);
    if (pos < 0)
        return;

    int endline_pos = buff.lastIndexOf("\n", pos) + 1;
    buff.insert(endline_pos,  stuff + "\n");

    f.seek(0);
    f.write(buff);
}

You could trim it down even more by not doing an insert and writing in three parts - up to endline_pos, stuff and after endline_pos. Then only one allocation would remain. I'll leave it as an exercise to the reader ;)

Same warning applies - don't use for large files.

vvolfster

You've got a couple of C++ answers :) If you are looking for QML / Js answer. You can pass your new line into the <line> param and the original text into <txt> param. The code is pretty short and mostly self explanatory. You are dividing the text into an array of lines by using the new line character "\n" and then inserting a new line into the list and putting it back together as one blob of text.

function insertAsSecondLastLine(line,txt) {
	var arr = !txt ? [] : txt.split("\n")
	if(arr.length > 0) {
		var lineNumber = arr.length - 1
		arr.splice(lineNumber,0,line);
	}
	else {
		arr.push(line);
	}
	return arr.join("\n")
}

AlvaroS

@raven-worx said:

@AlvaroS

QFile file(fileName);
if (file.open(QIODevice::ReadWrite | QIODevice::Text))
{
    // read lines
    QStringList lines;
    int lastIdx = -1;
    QTextStream in(&file);
    for( int i= 0; !in.atEnd(), ++i )
    {
        QString line = in.readLine();
        lines << line;
        if( line.contains("XXX") )
            lastIdx = i;
    }

    // insert your line
    lines.insert( lastIdx-1, ... );
    
    //write back to file
    file.seek(0);
    file.write( lines.join("\n") );
    
    file.close();
}

You should only use this code if the files aren't too big, since everything is loaded into the memory.
Also i left out some error checking and it's untested, but it should give you an idea.

Hello my friend.
First of all thanks a lot for answering.

I have tried what you say like this:

    QString fileName = QFileDialog::getOpenFileName(this,"indicate world","/home","files World (*.world)"); // We use the QFileDialog class to obtein the whole name file that user has choosen.
    QFile file(fileName);

    if (file.open(QIODevice::ReadWrite | QIODevice::Text))
    {
        // read lines
        QStringList lines;
        int lastIdx = -1;
        QTextStream in(&file);
        for( int i= 0; !in.atEnd(); ++i )
        {
            QString line = in.readLine();
            lines << line;
            if( line.contains("world") )
                lastIdx = i;
        }

        // insert your line
        lines.insert( lastIdx-1, "writting" );

        //write back to file
        file.seek(0);
        file.write( lines.join("\n") );

        file.close();
    }

But it give an error in "file.write( lines.join("\n") );" which is:
cpp:2106: error: no matching function for call to 'QFile::write(QString)'
file.write( lines.join("\n") );
^
Do you know why?

Thanks!!

AlvaroS

@Chris-Kawa said:

Here's a little shorter version, with a lot less allocations:
//insert stuff before line with last occurrence
void isblwlo(const QString& file, const QString& what, const QString& stuff)
{
    QFile f(file);
    if (!f.open(QIODevice::ReadWrite | QIODevice::Text))
        return;

    QByteArray buff = f.readAll();
    int pos = buff.lastIndexOf(what);
    if (pos < 0)
        return;

    int endline_pos = buff.lastIndexOf("\n", pos) + 1;
    buff.insert(endline_pos,  stuff + "\n");

    f.seek(0);
    f.write(buff);
}
You could trim it down even more by not doing an insert and writing in three parts - up to endline_pos, stuff and after endline_pos. Then only one allocation would remain. I'll leave it as an exercise to the reader ;)

Same warning applies - don't use for large files.

Thanks a lot, that works!

raven-worx

@AlvaroS said:

But it give an error in "file.write( lines.join("\n") );" which is:
cpp:2106: error: no matching function for call to 'QFile::write(QString)'
file.write( lines.join("\n") );
^

file.write( lines.join("\n").toUtf8() );

AlvaroS

@raven-worx Thanks!!!
This thread is solved :)