QFile class

shikamarucb

Hi all, I have a problem, and I want to edit a file system; the problem is that I want to delete a line of the file, but not how to do it properly; I have the following code and delete a "link" is removed from the file, but the file size remains the same; Visually is not no trace of the line but adds other invisible characters ...

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@#include "widget.h"
#include "ui_widget.h"
#include <QIODevice>
#include <QFile>
#include <QMessageBox>

Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
actualizar();
ui->quitlink->setEnabled(false);
connect(ui->buttlink,SIGNAL(clicked()),this,SLOT(on_pushButton_clicked()));
}

Widget::~Widget()
{
delete ui;
}

void Widget::on_pushButton_clicked()
{
QByteArray links(ui->link->text().toUtf8());
if(links.isEmpty()){
QMessageBox::warning(this,"Advertencia","Campo de direccion web vacio");
}else{
links=("\n1.1.1.1 "+links);
QFile texto("C:/Windows/System32/drivers/etc/hosts");
texto.open(QIODevice::Append | QIODevice::Text);
texto.write(links);
texto.flush();
texto.close();
}
actualizar();
}

void Widget::on_quitlink_clicked()
{

QString links=ui->linklist->currentItem()->text();
QString var;
//links="1.1.1.1 " +links;

QFile texto("C:/Windows/System32/drivers/etc/hosts");

texto.open(QIODevice::ReadWrite | QIODevice::Text);

while(!texto.atEnd()){
    var=texto.readLine();

    if(var.contains(links)){
        ui->link->setText(QString::number(var.length()));
        if(texto.pos()!=texto.size()){
            texto.seek(texto.pos()-links.length());
            for(int i=0;i<=links.length();i++){
                texto.write("\r");
                texto.flush();
            }
        }else{
            texto.seek(texto.pos()-links.length()-1);
            for(int i=0;i<=links.length();i++){
                texto.write("\r");
                texto.flush();
            }
        }
    }

}

texto.close();
ui->quitlink->setEnabled(false);
actualizar();

}

void Widget::on_linklist_clicked(const QModelIndex &index)
{
ui->quitlink->setEnabled(true);
}

void Widget::actualizar(){
ui->linklist->clear();

QFile texto("C:/Windows/System32/drivers/etc/hosts");
QString var;
texto.open(QIODevice::ReadOnly | QIODevice::Text);
while(!texto.atEnd()){
    var = texto.readLine();
    texto.flush();
    if(var.at(0)!= '#'){
        if(!var.isNull())
            ui->linklist->addItem(var);
    }
}
texto.close();

}
@

SGaist

Hi,

Removing some chars from a file doesn't necessarily modify its on disk size. A file is stored in one or more cluster which represent the minimum size of a file

shikamarucb

Hola de nuevo, se supone que los archivos de texto representan un byte por caracter y que a medida que yo quito o pongo caracteres,el archivo cambia su tamaño, esta es la unica manera que yo he encontrado para recorrer el archivo y eliminar datos, trata de compilar mi codigo y veras que al quedar un sola linea en el archivo, aparecen caracteres "fantasma" que no permiten un desplazamiento adecuado dentro del archivo.

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alex_malyu

The easiest approach I guess can be:

create (open) temporary file for writing.
open original file
in a loop until the end of the file:
read line from original file,
write line you want to keep to temporary file
rename temporary file

Hope this helps,
Alex

shikamarucb

Hello again, it is assumed that the text files represent one byte per character and as I remove or put characters, the file changes its size, this is the only way I've found to traverse the file and delete data; try to compile my code and see that to stay a single line in the file, characters "ghost" that do not adequately offset within the file appear.