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: " #define SEPARATOE "#" class MyDB{ public: MyDB(const char* pathName) : hashOffset(0), dataOffset(0),writeDataLength(0),idxOffset(0),writeIdxLength(0) { 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
#include <string> #include "mydb.h" void MyDB::TestFunc(const char* key) { } std::string MyDB::Query(const char* key) { size_t offset = GetIndexOffsetBykey(key); if (0 == offset) return ""; size_t nextPtr = ReadPtr(idxFile, offset); size_t indexLength = ReadPtr(idxFile, offset + PTR_SZ); char* indexstr = new char[indexLength + 1]; idxFile.read(indexstr, indexLength); indexstr[indexLength] = ' '; std::string indexString(indexstr); delete[] indexstr; std::string keyString = indexString.substr(0, 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(-1); } } return true; } bool MyDB::Init() { OpenFileOrExit(idxFile,DBidxName); OpenFileOrExit(datFile, DBdataName); idxFile.seekg(0, std::ios_base::end); size_t len = idxFile.tellg(); hashOffset = 0; if (len != 0) return true; //进行初始化 idxFile.seekp(0, std::ios::beg); std::string ptrstr(PTR_SZ, ' '); ptrstr[PTR_SZ - 1] = '0'; //std::cout << ptrstr << std::endl; for (int i = 0; i < NHASH_DEF + 1; i++) idxFile << ptrstr; idxFile << ' '; idxFile.flush(); return true; } unsigned long MyDB::HashFunc(const char *key) { unsigned long hval = 0; char c; int i; for (i = 1; (c = *key++) != 0; 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 = 0; char ptrstr[PTR_SZ + 1]; fs.seekg(offset, std::ios::beg); fs.read(ptrstr, PTR_SZ); ptrstr[PTR_SZ] = ' '; 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 + 1]; idxFile.read(indexstr, indexLength); indexstr[indexLength] = ' '; std::string indexString(indexstr); delete[] indexstr; std::string keyString = indexString.substr(0, indexString.find_first_of(SEPARATOE)); if (keyString == std::string(key)) break; currentPtr = nextPtr; } while (0 != currentPtr); return currentPtr; } size_t MyDB::GetIndexOffsetBykey(const char* key) { size_t indexOff = 0; unsigned long hashKeyValue = HashFunc(key); size_t linkOffset = hashKeyValue*PTR_SZ + hashOffset; size_t idxOffset = ReadPtr(idxFile,linkOffset); if (0 == idxOffset) return 0; //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(0, 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 + 1]; sprintf(ptrstr, "%*d", PTR_SZ,0); std::string idxString(writeString); idxString += ptrstr; idxString += key; idxString += SEPARATOE; idxString += std::to_string(dataOffset); idxString += SEPARATOE; idxString += std::to_string(writeDataLength); idxString += " "; unsigned long size = idxString.size() - strlen(ptrstr) * 2; 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 (0 == idxInLinkHeadoffset) { DoWriteIndex(key, 0); 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 (0 != 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(0, std::ios::end); dataOffset = datFile.tellp(); datFile << data; } catch (std::exception& e) { std::cerr << e.what() << std::endl; exit(1); } return true; }
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("123"); db.Init(); for (int i = 0; i < 500; ++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 0; }
代码运行后 文件效果
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447 14724 22indexWrite445#5230#12 448 14762 22indexWrite446#5242#12 449 14800 22indexWrite447#5254#12 450 14838 22indexWrite448#5266#12 451 14876 22indexWrite449#5278#12 452 0 22indexWrite450#5290#12 453 14952 22indexWrite451#5302#12 454 14990 22indexWrite452#5314#12 455 15028 22indexWrite453#5326#12 456 15066 22indexWrite454#5338#12 457 15104 22indexWrite455#5350#12 458 15142 22indexWrite456#5362#12 459 15180 22indexWrite457#5374#12 460 15218 22indexWrite458#5386#12 461 15256 22indexWrite459#5398#12 462 2884 22indexWrite460#5410#12 463 15332 22indexWrite461#5422#12 464 15370 22indexWrite462#5434#12 465 15408 22indexWrite463#5446#12 466 15446 22indexWrite464#5458#12 467 16092 22indexWrite465#5470#12 468 16130 22indexWrite466#5482#12 469 16168 22indexWrite467#5494#12 470 16206 22indexWrite468#5506#12 471 16244 22indexWrite469#5518#12 472 5034 22indexWrite470#5530#12 473 15712 22indexWrite471#5542#12 474 15750 22indexWrite472#5554#12 475 15788 22indexWrite473#5566#12 476 15826 22indexWrite474#5578#12 477 16472 22indexWrite475#5590#12 478 16510 22indexWrite476#5602#12 479 16548 22indexWrite477#5614#12 480 16586 22indexWrite478#5626#12 481 16624 22indexWrite479#5638#12 482 5414 22indexWrite480#5650#12 483 2668 22indexWrite481#5662#12 484 2380 22indexWrite482#5674#12 485 2092 22indexWrite483#5686#12 486 1172 22indexWrite484#5698#12 487 16852 22indexWrite485#5710#12 488 16890 22indexWrite486#5722#12 489 16928 22indexWrite487#5734#12 490 16966 22indexWrite488#5746#12 491 17004 22indexWrite489#5758#12 492 5794 22indexWrite490#5770#12 493 2704 22indexWrite491#5782#12 494 2416 22indexWrite492#5794#12 495 2128 22indexWrite493#5806#12 496 0 22indexWrite494#5818#12 497 17232 22indexWrite495#5830#12 498 17270 22indexWrite496#5842#12 499 17308 22indexWrite497#5854#12 500 17346 22indexWrite498#5866#12 501 17384 22indexWrite499#5878#12
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' '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
