C++精准判断/监控文件是否被修改的五种解决方案

#include <QFileInfo>
#include <QDateTime>

bool isFileModified(const QString& filePath, QDateTime& lastModified) {
    QFileInfo fileInfo(filePath);
    if(!fileInfo.exists()) return false;
    
    QDateTime currentModified = fileInfo.lastModified();
    if(currentModified != lastModified) {
        lastModified = currentModified;
        return true;
    }
    return false;
}

// 使用示例
QString configPath = "settings.conf";
QDateTime lastCheckTime = QFileInfo(configPath).lastModified();

// 定期检查
if(isFileModified(configPath, lastCheckTime)) {
    qDebug() << "配置文件已更新，重新加载...";
    loadConfig(configPath);
}

#include <QCryptographicHash>
#include <QFile>

QByteArray calculateFileHash(const QString& filePath) {
    QFile file(filePath);
    if(!file.open(QIODevice::ReadOnly)) {
        return QByteArray();
    }
    
    QCryptographicHash hash(QCryptographicHash::Sha256);
    if(hash.addData(&file)) {
        return hash.result();
    }
    return QByteArray();
}

// 使用示例
QString dataFile = "dataset.bin";
QByteArray lastHash = calculateFileHash(dataFile);

// 重要操作前校验
QByteArray currentHash = calculateFileHash(dataFile);
if(currentHash != lastHash) {
    qWarning() << "数据文件已被篡改！操作终止。";
    return;
}
processData(dataFile);

QByteArray calculateLargeFileHash(const QString& filePath) {
    QFile file(filePath);
    if(!file.open(QIODevice::ReadOnly)) return QByteArray();
    
    QCryptographicHash hash(QCryptographicHash::Sha256);
    const qint64 bufferSize = 1024 * 1024; // 1MB缓冲区
    QByteArray buffer(bufferSize, 0);
    
    while(!file.atEnd()) {
        qint64 bytesRead = file.read(buffer.data(), bufferSize);
        hash.addData(buffer.constData(), bytesRead);
    }
    
    return hash.result();
}

bool isFileChanged(const QString& filePath, 
                  QDateTime& lastModified, 
                  qint64& lastSize) {
    QFileInfo info(filePath);
    if(!info.exists()) return false;
    
    QDateTime currentModified = info.lastModified();
    qint64 currentSize = info.size();
    
    if(currentModified != lastModified || currentSize != lastSize) {
        lastModified = currentModified;
        lastSize = currentSize;
        return true;
    }
    return false;
}

// 使用示例 - 日志监控
QString logPath = "application.log";
QDateTime logTime;
qint64 logSize = 0;

// 初始化
QFileInfo(logPath).lastModified();
logSize = QFileInfo(logPath).size();

// 定时检查
if(isFileChanged(logPath, logTime, logSize)) {
    qDebug() << "发现新日志内容，开始分析...";
    analyzeNewLogEntries(logPath);
}

#include <QFileSystemWatcher>
#include <QDebug>

class FileMonitor : public QObject {
    Q_OBJECT
public:
    explicit FileMonitor(QObject *parent = nullptr)
        : QObject(parent) {
        connect(&watcher, &QFileSystemWatcher::fileChanged,
                this, &FileMonitor::onFileChanged);
    }
    
    void addFile(const QString& path) {
        watcher.addPath(path);
        monitoredFiles.insert(path);
    }
    
signals:
    void fileModified(const QString& path);
    
private slots:
    void onFileChanged(const QString &path) {
        qDebug() << "文件变更:" << path;
        
        // 处理Linux系统inotify的不足
        if(!QFile::exists(path)) {
            qDebug() << "文件可能被删除或移动";
        } else {
            // 重新添加监控（部分系统在修改后会移除监控）
            watcher.addPath(path);
            emit fileModified(path);
        }
    }
    
private:
    QFileSystemWatcher watcher;
    QSet<QString> monitoredFiles;
};

// 使用示例
FileMonitor monitor;
monitor.addFile("important_data.json");

QObject::connect(&monitor, &FileMonitor::fileModified, [](const QString& path){
    qDebug() << "实时加载更新文件:" << path;
    loadData(path);
});

class FileChangeDetector {
public:
    FileChangeDetector(const QString& path) 
        : filePath(path) {
        QFileInfo info(filePath);
        lastModified = info.lastModified();
        lastSize = info.size();
        lastHash = calculateQuickHash();
    }
    
    bool checkChanged() {
        QFileInfo info(filePath);
        if(!info.exists()) return false;
        
        // 第一层：元数据检查
        if(info.lastModified() != lastModified || 
           info.size() != lastSize) {
            
            // 第二层：快速哈希校验
            QByteArray currentQuickHash = calculateQuickHash();
            if(currentQuickHash != lastHash) {
                updateState(info, currentQuickHash);
                return true;
            }
        }
        return false;
    }

private:
    QByteArray calculateQuickHash() {
        QFile file(filePath);
        if(!file.open(QIODevice::ReadOnly)) return QByteArray();
        
        // 仅计算文件头部哈希，提升性能
        const qint64 sampleSize = 1024; // 1KB
        QByteArray header = file.read(sampleSize);
        return QCryptographicHash::hash(header, 
                      QCryptographicHash::Sha256);
    }
    
    void updateState(const QFileInfo& info, 
                    const QByteArray& hash) {
        lastModified = info.lastModified();
        lastSize = info.size();
        lastHash = hash;
    }
    
    QString filePath;
    QDateTime lastModified;
    qint64 lastSize;
    QByteArray lastHash;
};

// 使用示例
FileChangeDetector detector("user_data.db");
if(detector.checkChanged()) {
    qDebug() << "数据库文件已变更，执行备份操作";
    backupDatabase();
}

// Windows长路径支持
QString winPath = R"(\\?\C:\very\long\path\file.txt)";

// Linux inotify限制检查
int maxUserWatches = QFile("/proc/sys/fs/inotify/max_user_watches")
                    .readAll().toInt();
if(watchedFiles.count() > maxUserWatches * 0.8) {
    qWarning() << "接近inotify监控上限，考虑优化监控策略";
}

// 定时轮询优化 - QTimer节流
QTimer checkTimer;
checkTimer.setInterval(1000); // 1秒间隔
QObject::connect(&checkTimer, &QTimer::timeout, []{
    checkFiles();
});
checkTimer.start();

// 文件分组检查 - 避免高频IO
QThreadPool::globalInstance()->start([]{
    for(const auto& group : fileGroups) {
        checkFileGroup(group);
    }
});

// 处理文件被删除的情况
if(!QFileInfo::exists(filePath)) {
    if(watcher.files().contains(filePath)) {
        watcher.removePath(filePath);
    }
    qDebug() << "监控文件已被删除:" << filePath;
    return;
}

// 处理文件锁定情况
QFile file(filePath);
if(!file.open(QIODevice::ReadOnly)) {
    if(file.error() == QFile::ResourceError) {
        qDebug() << "文件被其他进程锁定，稍后重试";
        QTimer::singleShot(500, [=]{ checkFileLater(filePath); });
    }
    return;
}