跟着上一篇继续。本篇介绍 Qt 重新造的轮子：容器系统和文件操作系统。

1 容器

按理说标准库里面就有各种容器的实现了，这里重新造轮子了？

容器分为了两类：序列容器 和 关联容器。

1.1 QVector

动态数组容器，内部本质就是内存连续的数组，从而使得随机存取的效率非常高。但是对于元素的删除插入操作性能会比较差。对于长度很大的序列，推荐采用链表实现的的QList。

QVector的例子如下。使用非常简单，不再赘述。

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#include <QVector>
#include <QTextStream>

int main(void) {

    QTextStream out(stdout);

    QVector<int> vals = {1, 2, 3, 4, 5};

    out << "The size of the vector is: " << vals.size() << endl;

    out << "The first item is: " << vals.first() << endl;
    out << "The last item is: " << vals.last() << endl;

    vals.append(6);
    vals.prepend(0);

    out << "Elements: ";

    for (int val : vals) {
        out << val << " ";
    }

    out << endl;

    return 0;
}

1.2 QList

QList 也是序列容器，内部是链表实现。其随机访问、删除、插入操作效率都比较高。因此是 Qt 中最常用的容器。参考下面👇这个例子。

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#include <QTextStream>
#include <QList>
#include <algorithm>

int main(void) {

    QTextStream out(stdout);

    QList<QString> authors = {"Balzac", "Tolstoy", 
        "Gulbranssen", "London"};
  
    for (int i=0; i < authors.size(); ++i) {
  
        out << authors.at(i) << endl;
    }  
  
    authors << "Galsworthy" << "Sienkiewicz";

    out << "***********************" << endl;

    std::sort(authors.begin(), authors.end());

    out << "Sorted:" << endl;
    for (QString author : authors) {
  
        out << author << endl;
    }  
}

1.3 QStringList

为字符串做了优化的列表。

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#include <QTextStream>
#include <QList>

int main(void) {

    QTextStream out(stdout);

    QString string = "coin, book, cup, pencil, clock, bookmark";
    QStringList items = string.split(",");
    QStringListIterator it(items);

    while (it.hasNext()) {
        out << it.next().trimmed() << endl;
    }
}

1.4 QSet

集合可以确保其中存储的值是唯一的。

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#include <QSet>
#include <QList>
#include <QTextStream>
#include <algorithm>

int main(void) {

    QTextStream out(stdout);

    QSet<QString> cols1 = {"yellow", "red", "blue"};
    QSet<QString> cols2 = {"blue", "pink", "orange"};

    out << "There are " << cols1.size() << " values in the set" << endl;

    cols1.insert("brown");

    out << "There are " << cols1.size() << " values in the set" << endl;

    cols1.unite(cols2);

    out << "There are " << cols1.size() << " values in the set" << endl;

    for (QString val : cols1) {
        out << val << endl;
    }

    QList<QString> lcols = cols1.values();
    std::sort(lcols.begin(), lcols.end());

    out << "*********************" << endl;
    out << "Sorted:" << endl;

    for (QString val : lcols) {
        out << val << endl;
    }

   return 0;
}

可以看到合并(unite())后重复元素被移除了，只留下一份。

1.5 QMap

QMap是关联式容器，存储 key-value 对。下面是QMap使用的例子：

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#include <QTextStream>
#include <QMap>

int main(void) {

    QTextStream out(stdout);

    QMap<QString, int> items = { {"coins", 5}, {"books", 3} };

    items.insert("bottles", 7);

    QList<int> values = items.values();

    out << "Values:" << endl;

    for (int val : values) {
        out << val << endl;
    }

    QList<QString> keys = items.keys();

    out << "Keys:" << endl;
    for (QString key : keys) {
        out << key << endl;
    }

    QMapIterator<QString, int> it(items);

    out << "Pairs:" << endl;

    while (it.hasNext()) {
        it.next();
        out << it.key() << ": " << it.value() << endl;
    }
}

1.6 自定义排序

自定义排序其实就是要自定义比较函数。以下面的类为例：

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// book.h
class Book {

    public:
        Book(QString, QString);
        QString getAuthor() const;
        QString getTitle() const;

    private:
        QString author;
        QString title;
};
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// book.cpp
#include <QString>
#include "book.h"

Book::Book(QString auth, QString tit) {
    author = auth;
    title = tit;
}

QString Book::getAuthor() const {
    return author;
}

QString Book::getTitle() const {
    return title;
}

使用自定义的方式排序如下：

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#include <QTextStream>
#include <QList>
#include <algorithm> 
#include "book.h"

bool compareByTitle(const Book &b1, const Book &b2) {
    
  return b1.getTitle() < b2.getTitle();
}

int main(void) {

    QTextStream out(stdout);

    QList<Book> books = {
        Book("Jack London", "The Call of the Wild"),
        Book("Honoré de Balzac", "Father Goriot"),
        Book("Leo Tolstoy", "War and Peace"),
        Book("Gustave Flaubert", "Sentimental education"),
        Book("Guy de Maupassant", "Une vie"),
        Book("William Shakespeare", "Hamlet")
    };

    std::sort(books.begin(), books.end(), compareByTitle);

    for (Book book : books) {
        out << book.getAuthor() << ": " << book.getTitle() << endl;
    }
}

2 文件系统

这里涉及QFile, QDir, QFileInfo三个类。其中QFile负责操作文件（读取和写入），QDir提供了访问路径结构及其内容的接口，QFileInfo提供了与独立于操作系统的文件信息，包括文件名、文件存储的路径，访问时间，修改时间，权限，文件所有权信息。

2.1 文件大小

文件的大小通过QFileInfo::size()函数来获取。见下面的完整例子:

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#include <QTextStream>
#include <QFileInfo>

int main(int argc, char *argv[]) {

  QTextStream out(stdout);

  if (argc != 2) {
    qWarning("Usage: file_size file");
    return 1;
  }
  
  QString filename = argv[1];
  
  if (!QFile(filename).exists()) {
    qWarning("The file does not exist");
    return 1;
  }  
  
  QFileInfo fileinfo(filename);
  
  qint64 size = fileinfo.size();
  
  QString str = "The size is: %1 bytes";
  
  out << str.arg(size) << endl;
}

2.2 读取文件内容

读取文件之前需要打开文件，并基于这个文件创建流。

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#include <QTextStream>
#include <QFile>

int main(void) {
  QTextStream out(stdout);

  QFile file("colours");
  
  if (!file.open(QIODevice::ReadOnly)) {
    qWarning("Cannot open file for reading");
    return 1;
  }

  QTextStream in(&file);

  while (!in.atEnd()) {
    QString line = in.readLine();
    out << line << endl;
  }

  file.close();
}

2.3 写入文件内容

要写入文件需要文件以写入模式打开。

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#include <QTextStream>
#include <QFile>

int main(void) {
    
  QTextStream out(stdout);
    
  QString filename = "distros";
  QFile file(filename);
  
  if (file.open(QIODevice::WriteOnly)) {
      
    QTextStream out(&file);
    out << "Xubuntu" << endl;
    out << "Arch" << endl;
    out << "Debian" << endl;
    out << "Redhat" << endl;
    out << "Slackware" << endl;
    
  } else {
      
    qWarning("Could not open file");
  }  
  
  file.close(); 
}

2.4 复制文件

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#include <QTextStream>
#include <QFile>

int main(int argc, char *argv[]) {
  QTextStream out(stdout);
  
  if (argc != 3) {
      qWarning("Usage: copyfile source destination");
      return 1;
  }
  
  QString source = argv[1];
  
  if (!QFile(source).exists()) {
      qWarning("The source file does not exist");
      return 1;
  }
  
  QString destin(argv[2]);

  QFile::copy(source, destin);
}

2.5 文件信息的获取

  • 文件所有者：QFileInfo::group()和QFileInfo::owner()，返回的都是QString;
  • 修改时间: QFileInfo::lastRead()和QFileInfo::lastModified()，返回的是QDateTime;
  • 文件路径：参见下面的例子
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// filepath.cpp
#include <QTextStream>
#include <QFileInfo>

int main(int argc, char *argv[]) {
  QTextStream out(stdout);

  if (argc != 2) {
      out << "Usage: file_times file" << endl;
      return 1;
  }
  
  QString filename = argv[1];
  
  QFileInfo fileinfo(filename);
  
  QString absPath = fileinfo.absoluteFilePath();
  QString baseName = fileinfo.baseName();
  QString compBaseName = fileinfo.completeBaseName();
  QString fileName = fileinfo.fileName();
  QString suffix = fileinfo.suffix();
  QString compSuffix = fileinfo.completeSuffix();
  
  out << "Absolute file path: " << absPath << endl;
  out << "Base name: " << baseName << endl;
  out << "Complete base name: " << compBaseName << endl;
  out << "File name: " << fileName << endl;
  out << "Suffix: " << suffix << endl;
  out << "Whole suffix: " << compSuffix << endl;
}

输出为

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$ ./file_path ~/Downloads/qt-everywhere-opensource-src-5.5.1.tar.gz 
Absolute file path: /home/janbodnar/Downloads/qt-everywhere-opensource-src-5.5.1.tar.gz
Base name: qt-everywhere-opensource-src-5
Complete base name: qt-everywhere-opensource-src-5.5.1.tar
File name: qt-everywhere-opensource-src-5.5.1.tar.gz
Suffix: gz
Whole suffix: 5.1.tar.gz
  • 权限信息：通过QFile::permissions方法可以权限信息，具体的例子如下：
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#include <QTextStream>
#include <QFile>

int main(int argc, char *argv[]) {
  QTextStream out(stdout);

  if (argc != 2) {
      out << "Usage: permissions file" << endl;
      return 1;
  }
  
  QString filename = argv[1];
  
  QFile::Permissions ps = QFile::permissions(filename);
  
  QString fper;
  
  if (ps & QFile::ReadOwner) {
      fper.append('r');
  } else {
      fper.append('-');
  }
  
  if (ps & QFile::WriteOwner) {
      fper.append('w');
  } else {
      fper.append('-');
  }  
  
  if (ps & QFile::ExeOwner) {
      fper.append('x');
  } else {
      fper.append('-');
  }
  
  if (ps & QFile::ReadGroup) {
      fper.append('r');
  } else {
      fper.append('-');
  }
  
  if (ps & QFile::WriteGroup) {
      fper.append('w');
  } else {
      fper.append('-');
  }  
  
  if (ps & QFile::ExeGroup) {
      fper.append('x');
  } else {
      fper.append('-');
  }
  
  if (ps & QFile::ReadOther) {
      fper.append('r');
  } else {
      fper.append('-');
  }
  
  if (ps & QFile::WriteOther) {
      fper.append('w');
  } else {
      fper.append('-');
  }  
  
  if (ps & QFile::ExeOther) {
      fper.append('x');
  } else {
      fper.append('-');
  }
  
  out << fper << endl;
}

2.6 操作路径(directories)

  • 创建文件夹: QDir::mkdir()，返回布尔值表明创建是否成功。QDir::mkpath()也是创建文件夹 ，其区别在于mkpath()函数会同时创建缺少的父文件夹。
  • 重命名: QDir::exists(), 文件是否存在。
  • 获取 一些特殊的文件夹的位置：
    • QDir::currentPath()
    • QDir::homePath()
    • QDir::tempPath()
    • QDir::rootPath()
  • 输出文件夹内的内容
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#include <QTextStream>
#include <QFileInfo>
#include <QDir>

int main(int argc, char *argv[]) {
  QTextStream out(stdout);

  if (argc != 2) {
      qWarning("Usage: list_dir directory");
      return 1;
  }
  
  QString directory = argv[1];
  
  QDir dir(directory);
  
  if (!dir.exists()) {
      qWarning("The directory does not exist");
      return 1;
  }  
  
  dir.setFilter(QDir::Files | QDir::AllDirs);
  dir.setSorting(QDir::Size | QDir::Reversed);

  QFileInfoList list = dir.entryInfoList();
  
  int max_size = 0;
  
  foreach (QFileInfo finfo, list) {
      QString name = finfo.fileName();
      int size = name.size();
      if (size > max_size) {
          max_size = size;
      }
  }
  
  int len = max_size + 2;
  
  out << QString("Filename").leftJustified(len).append("Bytes") << endl;
  
  for (int i = 0; i < list.size(); ++i) {
    QFileInfo fileInfo = list.at(i);
    QString str = fileInfo.fileName().leftJustified(len);
    str.append(QString("%1").arg(fileInfo.size()));
    out << str << endl;
  }

  return 0;
}