(利用索引)大数据查询

秒速五厘米 2021-09-22 08:46 436阅读 0赞

编译环境:QT5(创建时选择的是widget)

主要是将一个大文件拆成多个小文件，这样子就能够大大地节省了搜索的时间。

主要代码如下：

main.cpp

#include "widget.h"
    #include <QApplication>
    
    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);
        Widget w;
        w.resize(600,400);
        w.show();
    
        return a.exec();
    }

widget.cpp

#include "widget.h"
    #include <QHBoxLayout>
    #include <QVBoxLayout>
    #include <QMessageBox>
    #include <QTextCodec>        //ASCII转UTF-8
    #include <QCursor>
    
    #include <time.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    Widget::Widget(QWidget *parent)
        : QWidget(parent)
    {
        setWindowTitle("酒店入住记录查询");
        label1=new QLabel();
        label1->setText("文件大小1.27GB\n记录数20151574");
        label2=new QLabel();
        label2->setText("请输入要查询的姓名:");
    
        btn1=new QPushButton();
        btn1->setText("查询");
        edit1=new QLineEdit();
        text1=new QTextBrowser();
    
        QHBoxLayout *layout1=new QHBoxLayout();
        layout1->addWidget(label2);
        layout1->addWidget(edit1);
        layout1->addWidget(btn1);
    
        QVBoxLayout *layout2=new QVBoxLayout(this);
        layout2->addWidget(label1);
        layout2->addLayout(layout1);
        layout2->addWidget(text1);
    
        connect(btn1,SIGNAL(clicked()),this,SLOT(on_clicked()));   //将btn1与on_clicked()关联
    }
    
    Widget::~Widget()
    {
    
    }
    
    void Widget::select(int n)  //n==1代表查询原始数据文件 n==2查询索引文件
    {
        clock_t start=clock();  //执行效率计时开始
    
        QTextCodec *codec=QTextCodec::codecForName("GBK");
    
        char key[2048]={0};
        char content[2048]={0};
    
        const char*s= codec->fromUnicode(edit1->text().trimmed()).data();//将edit1中的内容从QString转化为const char*
        strcpy(key,s);
    
        if(strlen(key)<4)
        {
            QMessageBox::information(this,"错误","输入不正确，请重新输入");
            return;
        }
        key[strlen(key)]=',';
    
        char path[1024]={0};
        if(n == 1)
            strcpy(path,"D:/Documents/code/hotel/db/kaifang_noBomb.txt");
        else if(n ==2)
        {
            int index=((unsigned char)key[0]+(unsigned char)key[1]+(unsigned char)key[2]+(unsigned char)key[3])%256;
            sprintf(path,"D:/Documents/code/hotel/db/index/%d.db",index);
        }
        FILE *p=fopen(path,"r");
        if(!p)
        {
            QString str=path;
            str+="打开失败";
            QMessageBox::information(this,"错误",str);
            return ;
        }
    
        this->setCursor(Qt::WaitCursor);
        text1->clear();
    
        unsigned int count=0;   //计数器
        while(!feof(p))
        {
            memset(content,0,sizeof(content));
            fgets(content,sizeof(content),p);
            if(content[strlen(content)-1] == '\n')
                content[strlen(content)-1]=0;
            if(strncmp(content,key,strlen(key))== 0)
            {
                text1->append(codec->toUnicode(content));
                count++;
            }
        }
        clock_t end=clock();
        this->setCursor(Qt::ArrowCursor);
        fclose(p);
        QString res="找到"+QString::number(count)+"条记录,用时"+QString::number(end-start)+"毫秒";
        QMessageBox::information(this,"完成",res);
    }
    
    void Widget::create_index()
    {
        clock_t start=clock();
        char path[1024]={0};
        strcpy(path,"D:/Documents/code/hotel/db/kaifang_noBomb.txt");
    
        FILE *p=fopen(path,"r");
        if(!p)
        {
            QString str=path;
            str+="打开失败";
            QMessageBox::information(this,"错误",str);
            return ;
        }
    
        FILE *pt[256]={NULL};
        //建立256个索引文件并打开
        for(int i=0;i<256;i++)
        {
            memset(path,0,sizeof(path));
            sprintf(path,"D:/Documents/code/hotel/db/index/%d.db",i);
            pt[i]=fopen(path,"w");
        }
        this->setCursor(Qt::WaitCursor);
    
        char buf[1024]={0};
        int index=0;    //索引值
        while(!feof(p))
        {
            memset(buf,0,sizeof(buf));
            fgets(buf,sizeof(buf),p);
            if(buf[strlen(buf)-1] == '\n')
                buf[strlen(buf)-1]=0;
            //根据关键字求索引键值
            index=((unsigned char)buf[0]+(unsigned char)buf[1]+(unsigned char)buf[2]+(unsigned char)buf[3])%256;
    
            fprintf(pt[index],"%s\n",buf);
        }
        fclose(p);
        for(int i=0;i<256;i++)
        {
            fclose(pt[i]);
        }
        clock_t end=clock();
        this->setCursor(Qt::ArrowCursor);
        QString res="用时"+QString::number(end-start)+"毫秒";
        QMessageBox::information(this,"完成",res);
    }
    
    void Widget::on_clicked()
    {
      //QMessageBox::information(this,"提示","按钮被按了");
        select(2);
    }

效果图:

![20171009190602149][]

[20171009190602149]: /images/20210920/2636174ae7724fba8d1f71db5abf1bee.png