Qt Creator module learning-files, directories and input/output (2)
This article is the focus of reading and writing files. I have used three ways to read and write files. If there are any shortcomings, I hope I can get your suggestions.
If you are a beginner, you can see:
Qt Creator module learning-files, directories and input/output (1)
2. Read and write files (using the basic QFile method)
For the convenience of description in this chapter, I will only write code, which is a small program.
The approximate shape is:
Realize the basic opening and saving files.
The slot function can be transferred to the slot using the designer interface,
//打开文件
void MainWindowoid MainWindow::on_pushButton_clicked()
{
QString filename = QFileDialog::getOpenFileName(this,
"open","../","TXT(*.txt)");
if(filename.isEmpty() == false){
QFile file(filename);
if(file.open(QIODevice::ReadOnly)==true){
//全部读完
//读文件,默认只识别utf8，如果想弄别的用文本流
/* QByteArray array = file.readAll();
//显示到编辑区
//ui->textEdit->setText(QString(array));
ui->textEdit->setText(array); */
//一行一行读
QByteArray array;
while(file.atEnd()==false){
//读一行
array = file.readLine();
}
ui->textEdit->setText(array);
}
file.close();
}
}
//保存文件
void MainWindow::on_pushButton_2_clicked()
{
QString filename = QFileDialog::getSaveFileName(this,"save","../","TXT(*.txt)");
if(filename.isEmpty()==false){
QFile file;//创建文件对象
//关联文件名字
file.setFileName(filename);
//打开文件，只写方式
if(file.open(QIODevice::WriteOnly)==true){
//获取内容
QString str = ui->textEdit->toPlainText();
//写文件
//把QString 转化为 QByteArray
file.write(str.toUtf8());
}
}
}3. Read and write files (using QDataStream to read and write)
This method is stored in binary, we usually call it data stream storage
#include "widget.h"
#include "ui_widget.h"
#include <QDataStream>
#include <QFile>
#include <QDebug>
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
writeData();
readData();
}
Widget::~Widget()
{
delete ui;
}
void Widget::writeData()
{
QFile file("../test.txt");
//打开文件，只写方式打开
if(file.open(QIODevice::WriteOnly)==true){
//创建数据流
//往数据流中输入数据
QDataStream stream(&file);
stream << QString("求点赞求关注")<<521;
file.close();
}
}
void Widget::readData()
{
QFile file("../test.txt");
//打开文件，只写方式打开
if(file.open(QIODevice::ReadOnly)==true){
//创建数据流
//往数据流中读取数据
QDataStream stream(&file);
//读的时候，按写的顺序取数据
QString str;
int a;
stream >> str >> a;
qDebug()<<str.toUtf8().data()<<a;
file.close();
}
}
Operation result:
u
4. Read and write files (using QTextStream to read and write)
This method is stored in the form of a text stream
#include "widget.h"
#include "ui_widget.h"
#include <QTextStream>
#include <QFile>
#include <QDebug>
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
writeData();
readData();
}
Widget::~Widget()
{
delete ui;
}
void Widget::writeData()
{
QFile file;
//此处的方式都可以，这里用不同的方式是为了让自己知道可以有好几种方式.
file.setFileName("../demo.txt");
//打开文件，只写方式打开
if(true==file.open(QIODevice::WriteOnly))
{
QTextStream stream(&file);
//指定编码,
stream.setCodec("UTF-8");
stream<<QString("求关注")<<521;
file.close();
}
}
void Widget::readData()
{
QFile file("../demo.txt");
//打开文件，只写方式打开
if(true==file.open(QIODevice::ReadOnly)){
QTextStream stream(&file);
//指定编码,
stream.setCodec("UTF-8");
QString str;
int a;
stream >> str >> a;
qDebug()<<str.toUtf8().data()<<a;
file.close();
}
}Operation result: In
this way, you can see that there is a 0 at the end of my output. This output itself is problematic, but it is not a big problem when using the interface design.
QString str = stream.readAll();
ui->textEdit->setText(str);There will be no problem with this.
5.buffer (memory file)
QByteArray array;
QBuffer memFile;
memFile.open(QIODevice::WriteOnly);
//加/n是换行
memFile.write("111\n");
memFile.write("222");
memFile.close();
qDebug()<<memFile.buffer();
qDebug()<<"array="<<array;
QBuffer memFile1;
memFile1.open(QIODevice::WriteOnly);
QDataStream stream(&memFile1);
stream<<QString("测试")<<521;
memFile1.close();
// 该方式读不出来
qDebug()<<QString(memFile1.buffer()).toUtf8().data();
memFile1.open(QIODevice::ReadOnly);
QDataStream stream1;
stream1.setDevice(&memFile1);
QString str;int a;
stream1>>str>>a;
memFile1.close();
qDebug()<<str.toUtf8().data()<<a;Results of operation:
Among the four methods, the one I use most as a student should be the first one. You can take a good look at the second and third methods. Personally, I feel very useful.