c++ - 在类中创建 vector 的 vector (二维数组)- 错误 :C++ requires a type specifier for all declarations

Question

因此，我在 C++ 中使用 Runge-Kutta 4(RK4) 方法程序化地编写了一种积分方程的方法。我目前正在尝试创建一个 RK4 类来为我的程序添加更多功能。但是，当我在类中设置我的二维数组时，我收到“C++ 需要所有声明的类型说明符”错误，这是我在原始程序中没有收到的。

起初，我使用的是 namespace std;，但是我遇到了一个回答，说那是糟糕的编程习惯，所以我删除了那行并改为调用 std::vector。我还确保包含 vector 库，但无济于事。

#include <iostream>
#include <stdio.h>
#include <math.h>
#include <vector>

class RK4 {
public:
    RK4(double x_i, double y_i, double z_i, double vx_i, double vy_i, double vz_i);
    //time-related stuff
    double dt = 0.01;
    int numtimes = 1000;

    int numvar = 3;
    double mu = 398589590898200.0;

    //setting up variables
    std::vector<vector<double> > position(numtimes,vector<double>(numvar));
    std::vector<vector<double> > velocity(numtimes,vector<double>(numvar));
    std::vector<vector<double> > rk1(numtimes,vector<double>(numvar));
    std::vector<vector<double> > rk2(numtimes,vector<double>(numvar));
    std::vector<vector<double> > rk3(numtimes,vector<double>(numvar));
    std::vector<vector<double> > rk4(numtimes,vector<double>(numvar));
    std::vector<vector<double> > vk1(numtimes,vector<double>(numvar));
    std::vector<vector<double> > vk2(numtimes,vector<double>(numvar));
    std::vector<vector<double> > vk3(numtimes,vector<double>(numvar));
    std::vector<vector<double> > vk4(numtimes,vector<double>(numvar));

这是我在原始程序中构建代码的方式，没有问题:

#include <iostream>
#include <ostream>
#include <cmath>
#include <vector>

using namespace std;

int main(){
// time related things
    //double t_i = 0; // initial time
    double dt = 0.01; // time step
    int numtimes = 10000; // how many steps taken

    vector<vector<double> > position(numtimes,vector<double>(numvar));
    vector<vector<double> > velocity(numtimes,vector<double>(numvar));

    vector<vector<double> > rk1(numtimes,vector<double>(numvar));
    vector<vector<double> > rk2(numtimes,vector<double>(numvar));
    vector<vector<double> > rk3(numtimes,vector<double>(numvar));
    vector<vector<double> > rk4(numtimes,vector<double>(numvar));
    vector<vector<double> > vk1(numtimes,vector<double>(numvar));
    vector<vector<double> > vk2(numtimes,vector<double>(numvar));
    vector<vector<double> > vk3(numtimes,vector<double>(numvar));
    vector<vector<double> > vk4(numtimes,vector<double>(numvar));
}

我不太清楚为什么这个调用在我原来的(程序)程序中有效，但在我当前的程序中却无效。

Answer 1

对于类，您不能在函数之外初始化成员。不过，您可以在构造函数中分配它们。

另外，你在一堆需要“std::vector”的地方写了“vector”。这应该修复它:

#include <math.h>
#include <stdio.h>
#include <iostream>
#include <vector>

class RK4 {
   public:
    RK4(double x_i, double y_i, double z_i, double vx_i, double vy_i, double vz_i) {
        double dt = 0.01;
        int numtimes = 1000;

        int numvar = 3;
        double mu = 398589590898200.0;

        //assigning the vectors
        position = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        velocity = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        rk1 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        rk2 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        rk3 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        rk4 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        vk1 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        vk2 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        vk3 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
        vk4 = std::vector<std::vector<double> >(numtimes, std::vector<double>(numvar));
    }
    //time-related stuff
    double dt = 0.01;
    int numtimes = 1000;

    int numvar = 3;
    double mu = 398589590898200.0;

    //declaring vectors
    std::vector<std::vector<double> > position;
    std::vector<std::vector<double> > velocity;
    std::vector<std::vector<double> > rk1;
    std::vector<std::vector<double> > rk2;
    std::vector<std::vector<double> > rk3;
    std::vector<std::vector<double> > rk4;
    std::vector<std::vector<double> > vk1;
    std::vector<std::vector<double> > vk2;
    std::vector<std::vector<double> > vk3;
    std::vector<std::vector<double> > vk4;
};

int main() {
    RK4 r(1, 1, 1, 1, 1, 1);

    return 0;
}