Question

我目前有一个使用我的模板作为其类型的向量：

vector<hashData> myTable;

hashData是一个类：

class hashData{
    public:
        // constructor for hashData
        hashData(hashType data){
            this->data = data;
            this->isActive = true;
            this->deleted = false;
        }

        hashData(){
            this->isActive = false;
            this->deleted = false;
        }

        // internal data for hashTable
        hashType data;
        bool deleted;
        bool isActive;
    };

当我尝试执行如下操作时：

vector<hashData> oldTable = myTable;

我收到此错误消息：

错误C2440：'初始化'：不能   从'std :: vector＆lt; _Ty＆gt;'转换至   '的std ::矢量＆lt;＆_Ty GT;'

hashtable.h（211）：错误C2440：   '初始化'：无法转换   '的std ::矢量＆lt;＆_Ty GT;'到大于'的std ::矢量＆lt;＆_Ty GT;'同   [_Ty = hashTable :: hashData]和[_Ty = unsigned long]

没有构造函数可以获取源类型，或构造函数重载解析不明确

有关为何发生这种情况的任何想法？我的参考资料似乎认为这是可能的，所以我不确定我的错误在哪里。

编辑：这是hashTable实现的完整头文件。我为代码的长度道歉，但我希望包含所有内容，因为我的初始“片段”似乎不够。

//驱动程序文件 #include“hashTable.h”

int main(void){
    // hash table creation
    hashTable<unsigned long> newTable(3);

    // hash table insertion
    newTable.addRecord(5);
    newTable.addRecord(6);
    newTable.addRecord(7);
    newTable.addRecord(8);
}

// hashTable头文件

// BEGIN HEADER FILE
#ifndef HASHTABLE_H
#define HASHTABLE_H

// Includes (system libraries)
#include <iostream>
#include <vector>

// Includes (custom libraries)

// Namespace
using namespace std;

// hashTable class
template <typename hashType>
class hashTable{
public:
    // constructor
    hashTable(int tableSize, string collisionMode = "Linear"){
        this->myTable.resize(optimizeTableSize(tableSize));
        this->collisionMode = collisionMode;
        this->activeRecords = 0;
    }

    // hashTable operations
    void addRecord(hashType);
    void deleteRecord(hashType);
    pair<bool,int> locateRecordPosition(hashType);
    bool searchRecord(hashType);
    hashType returnRecord(hashType);

    // hashTable mainteance
    void considerRehash();
    void rehashTable();
    int optimizeTableSize(int);

    // hashTable math
    bool isPrime(int);
    int nextPrime(int);

    // collision monitoring
    void collisionLogUpdate(int, string);
    int collisionLogAverage();

    // hash table internal class
    class hashData{
    public:
        // constructor for hashData
        hashData(hashType data){
            this->data = data;
            this->isActive = true;
            this->deleted = false;
        }

        hashData(){
            this->isActive = false;
            this->deleted = false;
        }

        // internal data for hashTable
        hashType data;
        bool deleted;
        bool isActive;
    };

private:
    // hashing function
    int calculateHash(hashType, int);

    // hashTable data structure
    vector<hashData> myTable;
    int activeRecords;

    // collision information
    deque<pair<int, string> > collisionLog;
    string collisionMode;
};

// hashTable implementation
// insert a record into the hash table
template <typename hashType>
void hashTable<hashType>::addRecord(hashType toAdd){
    // search for the record
    pair <bool, int> recordPos = locateRecordPosition(toAdd);

    // analyze the results
    if (recordPos.first == true) // the record already exists and is active
        return;
    // otherwise, go ahead and insert the record at this location
    myTable[recordPos.second] = hashData(toAdd);

    // update our count of active records
    activeRecords++;

    // consider a rehash of the hashTable
    considerRehash();
}

// delete a record from the hash table
template <typename hashType>
void hashTable<hashType>::deleteRecord(hashType toDelete){
    // search for the record
    pair <bool, int> recordPos = locateRecordPosition(toDelete);

    // analyze the results
    if (recordPos.first == false) // the record does not exist -- there is nothing to delete here!
        return;

    // otherwise, go ahead and perform a shallow deletion at this area
    myTable[recordPos.second].deleted = true;

    // update our count of active records
    activeRecords--;

    // consider a rehash of the hashTable
    considerRehash();
}

// find position of record within hash table (if such position exists)
template <typename hashType>
pair<bool,int> hashTable<hashType>::locateRecordPosition(hashType toFind){
    // setup data structures
    int collisionNum = 0;
    unsigned int currentPos;

    // search for the entry within the table
    currentPos = calculateHash(toFind, myTable.size());

    // enter a while loop for checking if we've found the item
    while(myTable.at(currentPos).isActive && !myTable.at(currentPos).deleted){
        // check to see if the entry found at the expected position matches
        if(myTable.at(currentPos).data == toFind){
            // update the collisionLog
            collisionLogUpdate(collisionNum,"locateRecord");

            // return the position of the item
            return pair<bool, int>(true,currentPos); // we've successfully found the item
        }

        // otherwise, we need to look for the correct location
        if (collisionMode == "Quadratic"){
            currentPos += 2 * ++collisionNum - 1;
            if(currentPos >= myTable.size())
                currentPos -= myTable.size();
        }
        else if (collisionMode == "Linear"){
            currentPos += 2 * ++collisionNum - 1;
            if(currentPos >= myTable.size())
                currentPos -= myTable.size();
        }

        // reloop and search again
    }

    // update the collisionLog
    collisionLogUpdate(collisionNum,"locateRecord");

    // if we escaped the loop, we were unable to find the item in the table -- return the first open location
    return pair<bool, int>(false,currentPos); // we didn't find the item
}

// return whether a record exists within hash table
template <typename hashType>
bool hashTable<hashType>::searchRecord(hashType toFind){
    return locateRecordPosition(toFind).first; // we didn't find the item
}

// return the contents of a record from the hash table
template <typename hashType>
hashType hashTable<hashType>::returnRecord(hashType toReturn){
    if (locateRecordPosition(toReturn).first) // if the record actually exists
        return myTable[locateRecordPosition(toReturn).second].data;
    else
        return hashType();
}

// calculate hash value
template <typename hashType>
int hashTable<hashType>::calculateHash(hashType toHash, int tableSize){
    if (toHash < 0) // if we have a negative number, change it prior to hashing
        toHash = (toHash*-1);
    return ((toHash*37) % tableSize);
}

// review the collision log and consider rehashing
template <typename hashType>
void hashTable<hashType>::considerRehash(){
    // check if we have used up more then half of the table, if we have, rehash
    if((activeRecords + 1) > ((signed) myTable.size() / 2))
        rehashTable();

    // check the current average of collisions
    // if the average number of collisions is greater then 20% of the table size (meaning it had to search through 20% of table), rehash
    else if((collisionLogAverage() > (myTable.size() * .20)) && (myTable.size() >= 100))
        rehashTable();

    // check the last operations number of collisions
    // if the number of collisions encounter is greater then 30% of the table size (meaning it had to search through 30% of table), rehash
    else if((collisionLog.back().first > (myTable.size() * .30)) && (myTable.size() >= 100))
        rehashTable();
}

// rehash the table
template <typename hashType>
void hashTable<hashType>::rehashTable(){
    // make a copy of the existing vector
    vector<hashType> oldTable = myTable;

    // reallocate myTable
    myTable.resize(optimizeTableSize(myTable.size() * 2)); // double the size of the current table

    // clear myTable
    myTable.clear();

    // copy the existing table over
    for (unsigned int i = 0; i < oldTable.size(); i++){
        if(oldTable[i].isActive && !oldTable[i].deleted){
            addRecord(oldTable[i].data);
        }
    }
}

// optimze table size
template <typename hashType>
int hashTable<hashType>::optimizeTableSize(int tableSize){
    // if we are performing quadratic probing, we need to optimize the table size to be a prime number, to prevent loops
    if (!isPrime(tableSize)){
        return nextPrime(tableSize);
    }

    // we only need to bother with optimizing the table size IF we are performing quadratic probing
    else
        return tableSize;
}

// determine if prime number
template <typename hashType>
bool hashTable<hashType>::isPrime(int numberToEvaluate){
    if(numberToEvaluate == 0)
        return true;

    numberToEvaluate = abs(numberToEvaluate);

    if(numberToEvaluate % 2 == 0) return true;

    for(int i = 3; i <= sqrt((float)numberToEvaluate); i+=2)
        if(numberToEvaluate % i == 0)
            return false;

    return true;
}

// find the next prime number
template <typename hashType>
int hashTable<hashType>::nextPrime(int numberToEvaluate){
    if (numberToEvaluate % 2 == 0)
        numberToEvaluate++;

    for (; !isPrime(numberToEvaluate); numberToEvaluate+=2)
        ;

    return numberToEvaluate;
}

// update collision log with a new entry
template <typename hashType>
void hashTable<hashType>::collisionLogUpdate(int numberOfCollisions, string operationPerformed){
    // add an entry to the log
    collisionLog.push_back(pair<int,string>(numberOfCollisions, operationPerformed));

    // verify we don't have more then 5 entires, if so, remove them
    while(collisionLog.size() > 5)
        collisionLog.pop_front();
}   

template <typename hashType>
int hashTable<hashType>::collisionLogAverage(){
    // add the last five entries, then take their average
    // the log should be maxed at five entries.. so just add them all

    // average holder
    int average;

    // loop through log
    for (unsigned int i = 0; i < collisionLog.size(); i++){
        average = collisionLog.at(i).first;
    }

    // average the sum
    average = average/5;

    // return the calculated average
    return average;
}   

// END HEADER FILE
#endif

Answer 1

myTable不是std::vector<hashData> - 请仔细检查它。

编辑：来源发布后。

vector<hashData> myTable;
vector<hashType> oldTable = myTable;

hashData！= hashType

Answer 2

hashtable.h（211）：错误C2440： '初始化'：无法转换 '的std ::矢量＆lt;＆_Ty GT;'到大于 '的std ::矢量＆lt;＆_Ty GT;'同 [_Ty = hashTable :: hashData]和 [_Ty = unsigned long]

看起来就像你做的那样

std::vector<hashData> oldTable = myTable;

其中 myTable 为std::vector<unsigned long>，不 std::vector<hashData>。

复制模板化的矢量

2 个答案: