c++ - 测试完美哈希函数时出现超出范围错误

Question

我正在尝试测试我的散列项目的功能之一。此函数的目标是为包含 1000 个字符串的列表中的字符串创建索引。它应该将字符串中每个字符的 ASCII 值相加，将它乘以一个随机数 (int c)，然后将它与一个素数 (int prime1) 取模，以在散列中找到索引。我试图用字符串“hi”测试这段代码，但每当我这样做时，我总是收到一个函数超出范围的错误。我不明白为什么 main 函数就在它试图测试的函数之下。

这是我的类(class)

 //using namespace std;
 #ifndef HASH_H
 #define HASH_H

 class hash{

 // Public Member functions
 public:
 hash(); // Constructor
 int  CreateG(const std::string city);
 int  HashFunction(std::string city); // the declaration of the hash function for the primary hash

 // Private member functions
 private:


 // Protected Member functions
 protected:

 }
 #endif 

这是我的.cpp

#include <cstdlib>
#include <iostream>
#include <string>
#include "Hash.h"

//using namespace std;

int  hash::HashFunction(std::string city){ // the declaration of the hash function for the primary hash


} 

int hash::CreateG(const std::string city){ // creates g(str) to use in the universal hash function 

    int prime1 = 16890581;
    int c = rand()%10; // This is the random number c to use when finding g 
    int g = 0; // initial value of g

    int x=0; // This is the sum of all the ascii values

    // Create a for loop, to iterate from 1 to 1000 (1000 because that this how many cities are in the input file)
    for(int i=1; i<=1000; i++){
        for( int t = 1; i < city.length(); t++ ) // for loop that runs through the string
        {
            char ch=city.at(i);
            int x=x+(int)ch; // This should be the running summation of the ascii values of the chars of the strings
        }
    }

    g = (x*c)%prime1;

    std::cout<<g;
    return g; // returns the value of 
}    



int main(){
    std:: string test = "hi";
    std::cout<<CreateG(test);
}

这是我的错误

   /home/ec2-user/environment/.c9/Project4/Hash.cpp:53:31: error: 
   ‘CreateG’ was not declared in this scope
    std::cout<<CreateG(test);
                           ^

Answer 1

CreateG是hash类的一个方法，不是一个独立的函数。

您必须实例化一个hash 才能使用它。

int main(){
    std:: string test = "hi";
    hash h;
    std::cout<<h.CreateG(test);
}