简易数据库实现 UNIX环境高级编程(APUE)第二十章 A Database Library

将课程的源代码使用C++写了一部分

LINUX WINDOW均可运行

#ifndef MYDB_H

#define MYDB_H

#include <iostream>

#include <fstream>

#include <string>

#define NHASH_DEF   137    /* default hash table size */

#define FREE_LINK  NHASH_DEF

#define PTR_SZ      8

#define MAGIC_WORDS "MyDB_Start:\n"

#define SEPARATOE    "#"

class MyDB{

public:

    MyDB(const char* pathName) : hashOffset(),

    dataOffset(),writeDataLength(),idxOffset(),writeIdxLength()

    {

        DBidxName = pathName;

        DBidxName += ".idx";

        DBdataName = pathName;

        DBdataName += ".dat";

    }

    void CloseDB(){

            idxFile.close();

            datFile.close();

        }

    ~MyDB(){ CloseDB();}

    bool Init();

    unsigned long HashFunc(const char *key);

    bool WriteData(const char* data);

    bool WriteIndex(const char* key);

    size_t GetIndexOffsetBykey(const char* key);

    long ReadPtr(std::fstream& fs, size_t offset);

    bool Writeptr(std::fstream& fs, size_t offset, const std::string& writeString);

    void TestFunc(const char* searchKey);

    size_t SearchLinkForKey(size_t offset, const char* key);

    std::string Query(const char* key);

private:

    bool DoWriteIndex(const char* key, const size_t nextOffset);

    bool OpenFileOrExit(std::fstream& fs, const std::string& fileName);

    size_t hashOffset;

    size_t dataOffset;

    size_t writeDataLength;

    unsigned long idxOffset;

    size_t writeIdxLength;

    MyDB& operator=(const MyDB&);

    MyDB(const MyDB&);

    std::string DBidxName;

    std::string DBdataName;

    std::fstream idxFile;

    std::fstream datFile;

};

#endif // MYDB_H

mydb.h

#include <string>

#include "mydb.h"

void MyDB::TestFunc(const char* key)

{

}

std::string MyDB::Query(const char* key)

{

    size_t offset = GetIndexOffsetBykey(key);

    if ( == offset)

        return "";

    size_t nextPtr = ReadPtr(idxFile, offset);

    size_t indexLength = ReadPtr(idxFile, offset + PTR_SZ);

    char* indexstr = new char[indexLength + ];

    idxFile.read(indexstr, indexLength);

    indexstr[indexLength] = '\0';

    std::string indexString(indexstr);

    delete[] indexstr;

    std::string keyString = indexString.substr(, indexString.find_first_of(SEPARATOE));

    return keyString;

}

bool MyDB::OpenFileOrExit(std::fstream& fs, const std::string& fileName) {

    fs.open(fileName, std::ios::in | std::ios::out | std::ios::binary);

    if (!fs.is_open()) {

        fs.open(fileName, std::ios::in | std::ios::out | std::ios::binary | std::ios::app);

        fs.close();

        fs.open(fileName, std::ios::in | std::ios::out | std::ios::binary);

        if (!fs.is_open()) {

            std::cerr << "open idxFile error.exit!" << std::endl;

            exit(-);

        }

    }

    return true;

}

bool MyDB::Init() {

    OpenFileOrExit(idxFile,DBidxName);

    OpenFileOrExit(datFile, DBdataName);

    idxFile.seekg(, std::ios_base::end);

    size_t len = idxFile.tellg();

    hashOffset = ;

    if (len != )

        return true;

    //进行初始化

    idxFile.seekp(, std::ios::beg);

    std::string ptrstr(PTR_SZ, ' ');

    ptrstr[PTR_SZ - ] = '';

    //std::cout << ptrstr << std::endl;

    for (int i = ; i < NHASH_DEF + ; i++)

        idxFile << ptrstr;

    idxFile << '\n';

    idxFile.flush();

    return true;

}

unsigned long

MyDB::HashFunc(const char *key)

{

    unsigned long   hval = ;

    char        c;

    int            i;

    for (i = ; (c = *key++) != ; i++)

        hval += c * i;

    return(hval % NHASH_DEF);

}

bool MyDB::Writeptr(std::fstream& fs,size_t offset,const std::string& writeString) {

    fs.seekp(offset, std::ios::beg);

    fs << writeString;

    return true;

}

long MyDB::ReadPtr(std::fstream& fs,size_t offset) {

    long ret = ;

    char ptrstr[PTR_SZ + ];

    fs.seekg(offset, std::ios::beg);

    fs.read(ptrstr, PTR_SZ);

    ptrstr[PTR_SZ] = '\0';

    ret = atol(ptrstr);

    return ret;

}

size_t MyDB::SearchLinkForKey(size_t offset, const char* key)

{

    size_t currentPtr = offset;

    do {

        size_t nextPtr = ReadPtr(idxFile, currentPtr);

        size_t indexLength = ReadPtr(idxFile, currentPtr + PTR_SZ);

        char* indexstr = new char[indexLength + ];

        idxFile.read(indexstr, indexLength);

        indexstr[indexLength] = '\0';

        std::string indexString(indexstr);

        delete[] indexstr;

        std::string keyString = indexString.substr(, indexString.find_first_of(SEPARATOE));

        if (keyString == std::string(key))

            break;

        currentPtr = nextPtr;

    } while ( != currentPtr);

    return currentPtr;

}

size_t MyDB::GetIndexOffsetBykey(const char* key) {

    size_t indexOff = ;

    unsigned long hashKeyValue = HashFunc(key);

    size_t linkOffset = hashKeyValue*PTR_SZ + hashOffset;

    size_t idxOffset = ReadPtr(idxFile,linkOffset);

    if ( == idxOffset)

        return ;

    //有链表  便历链表 查看是否已有关键字

    size_t offset = SearchLinkForKey(idxOffset,key);

    return offset;

}

bool MyDB::DoWriteIndex(const char* key,const size_t nextOffset) {

    idxFile.seekp(, std::ios::end);

    idxOffset = idxFile.tellp();

    std::string s = std::to_string(nextOffset);

    if (s.size() > PTR_SZ) {

        return false;

    }

    std::string writeString(PTR_SZ - s.size(), ' ');

    writeString += s;

    char ptrstr[PTR_SZ + ];

    sprintf(ptrstr, "%*d", PTR_SZ,);

    std::string idxString(writeString);

    idxString += ptrstr;

    idxString += key;

    idxString += SEPARATOE;

    idxString += std::to_string(dataOffset);

    idxString += SEPARATOE;

    idxString += std::to_string(writeDataLength);

    idxString += "\n";

    unsigned long size = idxString.size() - strlen(ptrstr) * ;

    sprintf(ptrstr, "%*d", PTR_SZ, size);

    idxString.replace(PTR_SZ, PTR_SZ, ptrstr);

    //std::cout << idxString << std::endl;

    idxFile << idxString;

    //idxFile.flush();

    return true;

}

bool MyDB::WriteIndex(const char* key)

{

    unsigned long hashKeyValue = HashFunc(key);

    size_t linkOffset = hashKeyValue*PTR_SZ + hashOffset;

    size_t idxInLinkHeadoffset = ReadPtr(idxFile, linkOffset);

    if ( == idxInLinkHeadoffset) {

        DoWriteIndex(key, );

        std::string s = std::to_string(idxOffset);

        if (s.size() <= PTR_SZ) {

            std::string writeString(PTR_SZ - s.size(), ' ');

            writeString += s;

            Writeptr(idxFile, linkOffset, writeString);

            return true;

        }

        else {

            return false;

        }

    }

    else {

        //在链表中寻找

        size_t offset = GetIndexOffsetBykey(key);

        if ( != offset) {

            //寻找到则直接返回

            return  true;

        }

        DoWriteIndex(key, idxInLinkHeadoffset);

        std::string s = std::to_string(idxOffset);

        if (s.size() <= PTR_SZ) {

            std::string writeString(PTR_SZ - s.size(), ' ');

            writeString += s;

            Writeptr(idxFile, linkOffset, writeString);

            return true;

        }

        else {

            return false;

        }

    }

    return true;

}

bool MyDB::WriteData(const char* data)

{

    try {

        writeDataLength = strlen(data);

        datFile.seekp(, std::ios::end);

        dataOffset = datFile.tellp();

        datFile << data;

    }

    catch (std::exception& e) {

        std::cerr << e.what() << std::endl;

        exit();

    }

    return true;

}

mydb.cpp

测试代码

// DB0_4.cpp : 定义控制台应用程序的入口点。

//

#include "stdafx.h"

#include <assert.h>

#include "mydb.h"

int main()

{

    MyDB db("");

    db.Init();

    for (int i = ; i < ; ++i) {

        std::string s = std::to_string(i);

        std::string writeIdxString("indexWrite");

        std::string writeDatString("dataWrite");

        writeIdxString += s;

        writeDatString += s;

        db.WriteData(writeDatString.c_str());

        db.WriteIndex(writeIdxString.c_str());

    }

    std::string queryKeyString1("indexWrite0");

    std::string queryKeyString2("indexWrite1");

    std::string queryKeyString3("indexWrite10");

    std::string queryKeyString4("indexWrite100");

    std::string queryKeyString5("indexWrite_");

    std::string queryKeyString6("indexWritex");

    std::string queryKeyString7("ShouldNotFind");

    assert(db.Query(queryKeyString1.c_str())  == queryKeyString1);

    assert(db.Query(queryKeyString2.c_str()) == queryKeyString2);

    assert(db.Query(queryKeyString3.c_str()) == queryKeyString3);

    assert(db.Query(queryKeyString4.c_str()) == queryKeyString4);

    assert(db.Query(queryKeyString5.c_str()) != queryKeyString5);

    assert(db.Query(queryKeyString6.c_str()) != queryKeyString6);

    assert(db.Query(queryKeyString7.c_str()) != queryKeyString7);

    std::cout << "fine" << std::endl;

    return ;

}

main.cpp

代码运行后文件效果

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大体思路如下：

使用两个文件分开存储 key 和value

value存储在data文件中中规中矩的存储不多描述

key值存储在index文件中使用素数(137)个桶来存储key值

0　　0　　0　　0　　0　　0.........0　　0 <-----137 个桶

当输入一个 kv 值时，比如输入 ''key" "value"

经过哈希运算 key的哈希值为2 则在第3个桶(计数规则从0开始，0,1,2)记录key写入index文件的偏移值

则index文件内容如下

0　　0　　1137　　0　　0　　0.......0　　0

0　8key#0#5

表示在第3个桶内有内容由于仅有一个记录所以INDEX的一开始为0 若有其他记录则记录桶内下个元素在文件里的偏移后面的8 表示接下来的字节加'\n'共长8个字节

后面的内容则是key值与data在data文件里的起始位置和长度

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(三) 一起学 Unix 环境高级编程 (APUE) 之文件和目录
. . . . . 目录 (一) 一起学 Unix 环境高级编程 (APUE) 之标准IO (二) 一起学 Unix 环境高级编程 (APUE) 之文件 IO (三) 一起学 Unix 环境高级编 ...
(五) 一起学 Unix 环境高级编程 (APUE) 之进程环境
. . . . . 目录 (一) 一起学 Unix 环境高级编程 (APUE) 之标准IO (二) 一起学 Unix 环境高级编程 (APUE) 之文件 IO (三) 一起学 Unix 环境高级编 ...
(六) 一起学 Unix 环境高级编程 (APUE) 之进程控制
. . . . . 目录 (一) 一起学 Unix 环境高级编程 (APUE) 之标准IO (二) 一起学 Unix 环境高级编程 (APUE) 之文件 IO (三) 一起学 Unix 环境高级编 ...
(七) 一起学 Unix 环境高级编程(APUE) 之进程关系和守护进程
. . . . . 目录 (一) 一起学 Unix 环境高级编程 (APUE) 之标准IO (二) 一起学 Unix 环境高级编程 (APUE) 之文件 IO (三) 一起学 Unix 环境高级编 ...
(八) 一起学 Unix 环境高级编程 (APUE) 之信号
. . . . . 目录 (一) 一起学 Unix 环境高级编程 (APUE) 之标准IO (二) 一起学 Unix 环境高级编程 (APUE) 之文件 IO (三) 一起学 Unix 环境高级编 ...

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