我应该如何在C++项目中声明全局变量？

Question

我有两个矩阵作为全局变量。但是，当我运行我的项目时，xCode中出现apache Mach-O链接器错误，表示我的全局变量声明了多次。我已经确定问题是我的全局变量的放置和头文件的导入。

我svd.h是在这里：

#ifndef __netflix_project__svd__ 
#define __netflix_project__svd__ 

#include <stdio.h> 
#include "dataManager.h" 

const float GLOBAL_AVG_SET1 = 3.608609; 
const float GLOBAL_AVG_SET2 = 3.608859; 

const int TOTAL_USERS = 458293; 
const int TOTAL_MOVIES = 17770; 

double **user_feature_table = new double *[TOTAL_USERS]; 
double **movie_feature_table = new double *[TOTAL_MOVIES]; 


void initialize(int num_features); 
void train(); 
double predictRating(int user, int movie); 




#endif /* defined(__netflix_project__svd__) */ 

我svd.cpp是在这里：

#include "svd.h" 



void initialize(int num_features) { 

    for(int i = 0; i < TOTAL_USERS; i++) { 

     user_feature_table[i] = new double[num_features]; 

     for(int k = 0; k < num_features; k++) { 
      user_feature_table[i][k] = GLOBAL_AVG_SET2/num_features; 
     } 
    } 

    for(int i = 0; i < TOTAL_MOVIES; i++) { 

     movie_feature_table[i] = new double[num_features]; 

     for(int k = 0; k < num_features; k++) { 
      movie_feature_table[i][k] = GLOBAL_AVG_SET2/num_features; 
     } 
    } 
} 

我的main.cpp看起来是这样的：

#include <iostream> 
#include "svd.h" 






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

    // Parse file and store test points as testPoint objects 
    std::vector<testPoint*> dataSet = fillTestPoints(); 


    // Get global average of data set 

    /* 
    double avg = getGlobalAverage(dataSet); 
    printf("%f", avg); 
    */ 
    initialize(30); 

    for(int i = 0; i < TOTAL_USERS; i++) { 
     printf("%f\n", user_feature_table[i][0]); 
    } 

    return 0; 
} 

我跑进之前的这个问题，但通过取出全局变量来修复它。然而，我确实需要优化这段代码，并且使用全局变量是实现它的方法，所以我需要弄清楚这一点。谢谢！

Answer 1

在头文件中，只有声明了他们。

extern const float GLOBAL_AVG_SET1; 
extern const float GLOBAL_AVG_SET2; 

extern const int TOTAL_USERS; 
extern const int TOTAL_MOVIES; 

extern double **user_feature_table; 
extern double **movie_feature_table; 

在您的.cpp文件之一，定义和初始化它们：

const float GLOBAL_AVG_SET1 = 3.608609; 
const float GLOBAL_AVG_SET2 = 3.608859; 

const int TOTAL_USERS = 458293; 
const int TOTAL_MOVIES = 17770; 

double **user_feature_table = new double *[TOTAL_USERS]; 
double **movie_feature_table = new double *[TOTAL_MOVIES];