c++ - 在头文件中声明一个类，并根据用户输入初始化该类的数组

Question

请查看下面我的 C++ 代码片段。因为 foo.h 在 int main(int argc, char *argv[]) 之前执行，数组 RedApple 将被初始化为 0 并导致错误。处理这个问题的最佳方法是什么？有没有办法将类声明保留在 foo.h 中，但根据用户输入在 foo.cpp 中对其进行初始化？谢谢!

在 foo.h 中

#include <vector>
extern int num;
class apple
{
std::vector<long> RedApple;
public:
    apple(): RedApple(num)
}

在 foo.cpp 中

#include    "foo.h"
int num;
int main(int argc, char *argv[])
{
sscanf_s(argv[1],"%d",&num);
}

Answer 1

在 foo.h 中

#include <vector>

class apple
{
std::vector<long> RedApple;
public:
    apple(){}
    apple(int num): RedApple(num){}
}

在 foo.cpp 中

#include    "foo.h"

int main(int argc, char *argv[])
{
    int num;
    sscanf_s(argv[1],"%d",&num);

    apple foo = num > 0 ? apple(num) : apple();
}

编辑:回应Klaus ' 提示我想我会添加初始化的解释，我正在评论 apple foo = num > 0 行？ apple(num) : apple(); 所以我会垂直打破它评论每个词:

apple      // This is the type of variable in the same way int is the type of int num;
foo        // The name of the apple object that I am creating
=          // Normally this will trigger the assignment operator (but in a declaration line the compiler will optimize it out)
num > 0 ?  // The condition to a ternary operator if true the statement before the : is executed if false the one after is executed
apple(num) // If num is greater than 0 use the non-default constructor
: apple(); // If num is less than or equal to 0 use the default number cause we can't initialize arrays negatively