我应该如何在我的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,我在xCode中得到一个apache Mach-O链接器错误,该错误表明我的全局变量被多次声明.我已确定问题是我的全局变量的放置和头文件的导入.

我的svd.h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__) */

我的svd.cpp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看起来像这样:

#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;
}

我之前遇到过这个问题,但是通过取出全局变量来修复它.但是,我确实需要优化此代码,并且使用全局变量是实现此目的的方法,因此我需要弄清楚这一点.谢谢!

Answer 1

在头文件中,只声明它们.

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;

在其中一个.cpp文件中,定义并初始化它们:

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];