Question

我正在尝试实施Google Dense Hash。这是我第一次使用C ++来处理比使用整数的简单向量更复杂的东西，所以我找不到问题，即使我觉得它应该很简单。

我粘贴了以下相关代码。

header.h：

#ifndef HEADER_H
#define HEADER_H

//#include <stdint.h>
#include <iostream>
#include <vector>
#include <ctime>
#include <fstream>
#include <boost/random.hpp>
#include <sparsehash/dense_hash_map>

#include "gene.h"
#include "genome.h"
#include "markovgraph.h"

//Debugger
#define DEBUG false
#define STATES false
#define MANUAL false

//Setting up the randomness
typedef boost::mt19937 RandomNumberGenerator;
typedef boost::uniform_int<> NumberDistribution;
typedef boost::variate_generator<RandomNumberGenerator&, NumberDistribution> Generator;

static RandomNumberGenerator generator;

#endif

traverse-markov.cc：

//Include the header
#include "header.h"

int main (int argc, char* argv[]) {

    //Default values of Controlvariables
    int initial_conditions = 100000; // Number of initial states to generate.
    int repeat_per_condition = 1; // Default number of initial states to generate.
    int iterations = 2000; // Number of steps to run.
    int seed = 1234; // Random seed to generate conditions
    bool synchronous = true;
    bool random_order = false;
    bool silent = false;
    bool false_feedback = false;
    bool same_states = false;
    int decay_counter = 0;
    int update_method = 0;
    std::string input_filename;
    std::string output_filename;
    std::string initial_condition_file;

    Markovgraph markov;
    markov.add_vertex("a");
    markov.add_vertex("a");
    markov.add_vertex("b");
    markov.add_vertex("c");

    markov.vertices_status();
    std::cout << "Number of vertices: " << markov.vertex_count() << std::endl;
    return 0;
}

markovgraph.h：

#ifndef MARKOVGRAPH_H
#define MARKOVGRAPH_H

extern uint64_t MurmurHash64A ( const void * key, int len, unsigned int seed );


// simple hash adapter for types without pointers
template<typename T>
struct MurmurHasher {
    size_t operator()(const T& t) const {
        return MurmurHash64A(&t, sizeof(t), 0);
    }    
};

// specialization for strings
template<>
struct MurmurHasher<std::string> {
    size_t operator()(const std::string& t) const {
        return MurmurHash64A(t.c_str(), t.size(), 0);
    }    
};

struct eqstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return (s1 == s2) || (s1 && s2 && (strcmp(s1, s2) == 0));
  }
};

typedef google::dense_hash_map<const char*, long int, MurmurHasher<const char*>, eqstr> dense_hash_t;

class Markovgraph {
    //Private variables
  dense_hash_t vertices;
  //google::dense_hash_map<const char*, long, MurmurHasher<const char*>, eqstr> edges;

    public:
        //Public variables

        //Functions
        Markovgraph(); //Constructor
    void add_vertex(std::string vertex);
    void print_vertex(std::string vertex);
    void vertices_status();
    int vertex_count();
    //add_edge(std::string upvertex,std::string downvertex);
    ~Markovgraph(); //Destructor
};

#endif

markovgraph.cc：

//Include the header
#include "header.h"

// 64-bit hash for 64-bit platforms
// copied from https://sites.google.com/site/murmurhash/
uint64_t MurmurHash64A ( const void * key, int len, unsigned int seed ) {
  const uint64_t m = 0xc6a4a7935bd1e995;
  const int r = 47;

  uint64_t h = seed ^ (len * m);

  const uint64_t * data = (const uint64_t *)key;
  const uint64_t * end = data + (len/8);

  while(data != end)
  {
    uint64_t k = *data++;

    k *= m; 
    k ^= k >> r; 
    k *= m; 

    h ^= k;
    h *= m; 
  }

  const unsigned char * data2 = (const unsigned char*)data;

  switch(len & 7)
  {
  case 7: h ^= uint64_t(data2[6]) << 48;
  case 6: h ^= uint64_t(data2[5]) << 40;
  case 5: h ^= uint64_t(data2[4]) << 32;
  case 4: h ^= uint64_t(data2[3]) << 24;
  case 3: h ^= uint64_t(data2[2]) << 16;
  case 2: h ^= uint64_t(data2[1]) << 8;
  case 1: h ^= uint64_t(data2[0]);
          h *= m;
  };

  h ^= h >> r;
  h *= m;
  h ^= h >> r;

  return h;
} 

//Constructor
Markovgraph::Markovgraph() {
    vertices.set_empty_key(NULL);
    //edges.set_empty_key(NULL);
}

//Add vertex function
void Markovgraph::add_vertex(std::string vertex) {
  vertices[vertex.c_str()] = 1;
}

//Print vertex function
void Markovgraph::print_vertex(std::string vertex) {
  std::cout << vertex << " --> " << vertices[vertex.c_str()] << std::endl;
}

//Print all vertices
void Markovgraph::vertices_status() {
  // Print whole hash table to cout
  for(dense_hash_t::const_iterator it = vertices.begin(); it != vertices.end(); it++){
    std::cout << it->first << " --> " << it->second << std::endl;
  }
}

//Vertex count
int Markovgraph::vertex_count() {
  return vertices.size();
}



//Destructor
Markovgraph::~Markovgraph() {
    //Destroy things...
}

输出结果为：

c --> 1
Number of vertices: 1

所以不知何故只保存了最后一个“顶点”。我尝试使用markov.add_vertex（）添加的早期键/值对消失了。

我希望你能帮助我，因为我已经待了一个多星期。

Answer 1

void Markovgraph::add_vertex(std::string vertex) {
  vertices[vertex.c_str()] = 1;
}

将导致指向保存add_vertex的本地字符串的指针，一旦离开该函数，vertex将不再存在，因此使用指针将是UB。

解决此问题的最简单方法可能是让您的密钥为std::string

如何防止重新初始化Google Hash

1 个答案: