(利用索引)大数据查询

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: