CompressingFile

4-4-CompressingFile/4-4-CompressingFile.pro

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+QT -= gui
+
+CONFIG += c++11 console
+CONFIG -= app_bundle
+
+# The following define makes your compiler emit warnings if you use
+# any Qt feature that has been marked deprecated (the exact warnings
+# depend on your compiler). Please consult the documentation of the
+# deprecated API in order to know how to port your code away from it.
+DEFINES += QT_DEPRECATED_WARNINGS
+
+# You can also make your code fail to compile if it uses deprecated APIs.
+# In order to do so, uncomment the following line.
+# You can also select to disable deprecated APIs only up to a certain version of Qt.
+#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
+
+SOURCES += \
+        main.cpp
+
+# Default rules for deployment.
+qnx: target.path = /tmp/$${TARGET}/bin
+else: unix:!android: target.path = /opt/$${TARGET}/bin
+!isEmpty(target.path): INSTALLS += target

4-4-CompressingFile/main.cpp

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+#include <QCoreApplication>
+#include <QDebug>
+#include <QFile>
+#include <QDir>
+#include <QBuffer>
+#include <QTextStream>
+
+//Our own custom file format, will not work with anything else!!
+
+bool makeFile(QString path) {
+
+    QFile file(path);
+    if(file.open(QIODevice::WriteOnly)) {
+
+        QByteArray data;
+        for(int i = 0; i < 1000; i++) {
+            data.append(QString::number(i) + "\r\n");
+        }
+
+        file.write(data);
+
+        file.close();
+        return true;
+    }
+
+    return false;
+}
+
+QByteArray getHeader() {
+    QByteArray header;
+    header.append("@!~!@");
+    return header;
+}
+
+bool compressFile(QString originalFile, QString newFile) {
+    QFile ofile(originalFile);
+    QFile nfile(newFile);
+    QByteArray header = getHeader();
+
+    if(!ofile.open(QIODevice::ReadOnly)) return false;
+    if(!nfile.open(QIODevice::WriteOnly)) return  false;
+    int size = 1024;
+
+    while (!ofile.atEnd()) {
+        QByteArray buffer = ofile.read(size);
+        QByteArray compressed = qCompress(buffer);
+        qInfo() << "Header at:" << nfile.pos();
+        nfile.write(header);
+        qInfo() << "Size: " << nfile.write(compressed); // unknown size
+
+    }
+    ofile.close();
+    nfile.close();
+    return true;
+}
+
+bool decompressFile(QString originalFile, QString newFile) {
+    QFile ofile(originalFile);
+    QFile nfile(newFile);
+    QByteArray header = getHeader();
+    int size = 1024;
+
+    if(!ofile.open(QIODevice::ReadOnly)) return false;
+    if(!nfile.open(QIODevice::WriteOnly)) return false;
+
+    //Double check that WE compressed the file
+    QByteArray buffer = ofile.peek(size);
+    if(!buffer.startsWith(header)) {
+        qCritical() << "We did not create this file!";
+        ofile.close();
+        nfile.close();
+        return false;
+    }
+
+    //Find the header positions
+    ofile.seek(header.length());
+    qInfo() << "Starting at: " << ofile.pos();
+
+    while (!ofile.atEnd()) {
+        buffer = ofile.peek(size);
+        qint64 index = buffer.indexOf(header);
+        qInfo() << "Header found at:" << index;
+
+        if(index > -1) {
+            //Have the header!
+            qint64 maxbytes = index;
+            qInfo() << "Reading: " << maxbytes;
+            buffer = ofile.read(maxbytes);
+            ofile.read(header.length());
+        } else {
+            //Do not have the header!
+            qInfo() << "Read all, no header";
+            buffer = ofile.readAll();
+        }
+
+        QByteArray decompressed = qUncompress(buffer);
+        qInfo() << "Decompressed: " << nfile.write(decompressed);
+        nfile.flush();
+    }
+
+    ofile.close();
+    nfile.close();
+
+    return true;
+
+}
+
+int main(int argc, char *argv[])
+{
+    QCoreApplication a(argc, argv);
+
+    QString orginalFile = QDir::currentPath() + QDir::separator() + "orginal.txt";
+    QString compressedFile = QDir::currentPath() + QDir::separator() + "compressed.txt";
+    QString decompressedFile = QDir::currentPath() + QDir::separator() + "decompressed.txt";
+
+    if(makeFile(orginalFile)) {
+        qInfo() << "Original created";
+
+        if(compressFile(orginalFile, compressedFile)) {
+            qInfo() << "File compressed";
+            if(decompressFile(compressedFile,decompressedFile)) {
+                qInfo() << "File decompressed!";
+            } else {
+                qInfo() << "Could not decompress file!";
+            }
+        } else {
+            qInfo() << "File not compressed";
+        }
+
+
+    }
+
+    return a.exec();
+}