🗂️前言

📄ref

• Index of / (qt.io)

本文资料和测试版本为 Qt 5.15

📄访问标记

🗃️enum 标记

std::ios_base::openmode - cppreference.com

class QIODevice;

	enum OpenModeFlag {
        NotOpen = 0x0000,
        ReadOnly = 0x0001,
        WriteOnly = 0x0002,
        ReadWrite = ReadOnly | WriteOnly,
        Append = 0x0004,
        Truncate = 0x0008,
        Text = 0x0010,
        Unbuffered = 0x0020,
        NewOnly = 0x0040,
        ExistingOnly = 0x0080
    };
    Q_DECLARE_FLAGS(OpenMode, OpenModeFlag)

class QFileDevice;

    enum FileError {
        NoError = 0,
        ReadError = 1,
        WriteError = 2,
        FatalError = 3,
        ResourceError = 4,
        OpenError = 5,
        AbortError = 6,
        TimeOutError = 7,
        UnspecifiedError = 8,
        RemoveError = 9,
        RenameError = 10,
        PositionError = 11,
        ResizeError = 12,
        PermissionsError = 13,
        CopyError = 14
    };

    enum FileTime {
        FileAccessTime,
        FileBirthTime,
        FileMetadataChangeTime,
        FileModificationTime
    };

    enum Permission {
        ReadOwner = 0x4000, WriteOwner = 0x2000, ExeOwner = 0x1000,
        ReadUser  = 0x0400, WriteUser  = 0x0200, ExeUser  = 0x0100,
        ReadGroup = 0x0040, WriteGroup = 0x0020, ExeGroup = 0x0010,
        ReadOther = 0x0004, WriteOther = 0x0002, ExeOther = 0x0001
    };
    Q_DECLARE_FLAGS(Permissions, Permission)

    enum FileHandleFlag {
        AutoCloseHandle = 0x0001,
        DontCloseHandle = 0
    };
    Q_DECLARE_FLAGS(FileHandleFlags, FileHandleFlag)

🗂️Code

📄demo

qmake

QT += core

#DESTDIR = $$PWD/bin
CONFIG += c++11 console

SOURCES += \
        main.cpp

main.cpp

#include <QDebug>
#include <QFile>
#include <QString>

void check_qfile(QFile& file) {
    qWarning() << file.error() << file.errorString();
}

void file_write(QString file_path) {
    QFile file(file_path);
    if (file.open(QFile::WriteOnly) == false) {
        qDebug() << __func__;
        check_qfile(file);
        return;
    }

    QString name = "cuber-lotus";
    QString url  = "https://space.bilibili.com/8172252";
    /// QTextStream &endl(QTextStream &s)
    QTextStream(&file) << name << Qt::endl;
    /// QString -> QByteArray
    file.write(url.toLocal8Bit());

    qDebug() << __func__;
    check_qfile(file);
    file.close();
}

void file_read(QString file_path) {
    QFile file(file_path);
    if (file.open(QFile::ReadOnly) == false) {
        qDebug() << __func__;
        check_qfile(file);
        return;
    }

    /// 直接读取全部
    /// QByteArray -> QString
    QByteArray byteArr = file.readAll();
    QString    msg     = byteArr;
    qDebug().noquote() << msg;

    qDebug() << __func__;
    check_qfile(file);
    file.close();
}

int main() {
    QString file_path = "example.txt";
    file_write(file_path);
    file_read(file_path);
}

📄分点讲解

🗃️继承体系

QIODevice是否继承于QObject取决于是否指定（编译时指定）。

####################
####  QIODevice  ### 
####################
        |
	    V
####################
#### QFileDevice ### 
####################
        |
	    V
####################
####    QFile    ### 
####################

🗃️打开/关闭

QFile file(file_path);
if (file.open(QFile::WriteOnly) == false) {
    return;
}

🗃️写

法1：

// 借助 QTextStream qt的文件流操作
QString name = "cuber-lotus";
/// QTextStream &endl(QTextStream &s)
QTextStream(&file) << name << Qt::endl;

法2：

// 使用自带的 write
QString url  = "https://space.bilibili.com/8172252";
/// QString -> QByteArray
file.write(url.toLocal8Bit());

qint64 write(const char *data, qint64 len);
qint64 write(const char *data);
inline qint64 write(const QByteArray &data)
{ return write(data.constData(), data.size()); }

🗃️读

• read
• reanLine
• readAll

qint64 read(char *data, qint64 maxlen);
QByteArray read(qint64 maxlen);
QByteArray readAll();
qint64 readLine(char *data, qint64 maxlen);
QByteArray readLine(qint64 maxlen = 0);
virtual bool canReadLine() const;

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🗂️END

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