我是c++的新手，我正试图编写一个程序，打开一个文件"parameters.txt"，其中有8个空格分隔的数字。然后我在一个单独的函数RK4()中使用这些数字来获得3个数组(y1, y2, t)。然后我在main()中操作这些数组并输出一个文件"output.txt"到工作目录
这是我的代码:
#include <string>
#include <iostream>
#include <cmath>
#include <fstream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <tuple>
using namespace std;
tuple<vector<double>, vector<double>, vector<double>> RK4() {
//open parameters.txt, put data into a vector
ifstream fin("parameters.txt");
vector<double> data;
int element;
while (fin >> element) {
data.push_back(element);
}
//define tspan
vector<double> tspan(2);
tspan[0] = 0.0;
tspan[1] = data[7];
//define y0
vector<double> y0(4);
y0[0] = data[4];
y0[1] = data[5];
y0[2] = 0.0;
y0[3] = 0.0;
double theta1 = y0[0];
double theta2 = y0[1];
double omega1 = y0[2];
double omega2 = y0[3];
//define stepSize
double stepSize;
stepSize = data[6];
//define range
int range = int(tspan[1] / stepSize);
//define other constants
double m1, m2, l1, l2;
m1 = data[0];
m2 = data[1];
l1 = data[2];
l2 = data[3];
double g = 9.81;
//define y, t vectors
vector<double> y1(range);
vector<double> y2(range);
vector<double> y3(range);
vector<double> y4(range);
vector<double> t(range);
for (double i = 0.0; i < 1.0 * range; i++) {
t[i] = i * stepSize;
}
//enter y0 into first value
y1[0] = theta1;
y2[0] = theta2;
y3[0] = omega1;
y4[0] = omega2;
//loop to find y, t vectors
for (int i = 0; i < range - 1; i++) {
//finding all k values:
//k1
double dTheta1_1 = y3[i];
double dOmega1_1 = (-g * (2 * m1 + m2) * sin(y1[i]) - m2 * g * sin(y1[i] - 2 * y2[i]) - 2 * sin(y1[i] - y2[i]) * m2 * (pow(y4[i], 2) * l2 + pow(y3[i], 2) * l1 * cos(y1[i] - y2[i]))) / (l1 * (2 * m1 + m2 - m2 * cos(2 * y1[i] - 2 * y2[i])));
double dTheta2_1 = y4[i];
double dOmega2_1 = (2 * sin(y1[i] - y2[i]) * (pow(y3[i], 2) * l1 * (m1 + m2) + g * (m1 + m2) * cos(y1[i]) + pow(y4[i], 2) * l2 * m2 * cos(y1[i] - y2[i]))) / (l2 * (2 * m1 + m2 - m2 * cos(2 * y1[i] - 2 * y2[i])));
//k2
double dTheta1_2 = y3[i] + 0.5 * stepSize * dTheta1_1;
double dOmega1_2 = (-g * (2 * m1 + m2) * sin(y1[i] + 0.5 * stepSize * dTheta1_1) - m2 * g * sin((y1[i] + 0.5 * stepSize * dTheta1_1) - 2 * (y2[i] + 0.5 * stepSize * dTheta2_1)) - 2 * sin((y1[i] + 0.5 * stepSize * dTheta1_1) - (y2[i] + 0.5 * stepSize * dTheta2_1)) * m2 * (pow(y4[i] + 0.5 * stepSize * dOmega2_1, 2) * l2 + pow(y3[i] + 0.5 * stepSize * dOmega1_1, 2) * l1 * cos((y1[i] + 0.5 * stepSize * dTheta1_1) - (y2[i] + 0.5 * stepSize * dTheta2_1)))) / (l1 * (2 * m1 + m2 - m2 * cos(2 * (y1[i] + 0.5 * stepSize * dTheta1_1) - 2 * (y2[i] + 0.5 * stepSize * dTheta2_1))));
double dTheta2_2 = y4[i] + 0.5 * stepSize * dTheta2_1;
double dOmega2_2 = (2 * sin((y1[i] + 0.5 * stepSize * dTheta1_1) - (y2[i] + 0.5 * stepSize * dTheta2_1)) * (pow(y3[i] + 0.5 * stepSize * dOmega1_1, 2) * l1 * (m1 + m2) + g * (m1 + m2) * cos(y1[i] + 0.5 * stepSize * dTheta1_1) + pow(y4[i] + 0.5 * stepSize * dOmega2_1, 2) * l2 * m2 * cos((y1[i] + 0.5 * stepSize * dTheta1_1) - (y2[i] + 0.5 * stepSize * dTheta2_1)))) / (l2 * (2 * m1 + m2 - m2 * cos(2 * (y1[i] + 0.5 * stepSize * dTheta1_1) - 2 * (y2[i] + 0.5 * stepSize * dTheta2_1))));
//k3
double dTheta1_3 = y3[i] + 0.5 * stepSize * dTheta1_2;
double dOmega1_3 = (-g * (2 * m1 + m2) * sin(y1[i] + 0.5 * stepSize * dTheta1_2) - m2 * g * sin((y1[i] + 0.5 * stepSize * dTheta1_2) - 2 * (y2[i] + 0.5 * stepSize * dTheta2_2)) - 2 * sin((y1[i] + 0.5 * stepSize * dTheta1_2) - (y2[i] + 0.5 * stepSize * dTheta2_2)) * m2 * (pow(y4[i] + 0.5 * stepSize * dOmega2_2, 2) * l2 + pow(y3[i] + 0.5 * stepSize * dOmega1_2, 2) * l1 * cos((y1[i] + 0.5 * stepSize * dTheta1_2) - (y2[i] + 0.5 * stepSize * dTheta2_2)))) / (l1 * (2 * m1 + m2 - m2 * cos(2 * (y1[i] + 0.5 * stepSize * dTheta1_2) - 2 * (y2[i] + 0.5 * stepSize * dTheta2_2))));
double dTheta2_3 = y4[i] + 0.5 * stepSize * dTheta2_2;
double dOmega2_3 = (2 * sin((y1[i] + 0.5 * stepSize * dTheta1_2) - (y2[i] + 0.5 * stepSize * dTheta2_2)) * (pow(y3[i] + 0.5 * stepSize * dOmega1_2, 2) * l1 * (m1 + m2) + g * (m1 + m2) * cos(y1[i] + 0.5 * stepSize * dTheta1_2) + pow(y4[i] + 0.5 * stepSize * dOmega2_2, 2) * l2 * m2 * cos((y1[i] + 0.5 * stepSize * dTheta1_2) - (y2[i] + 0.5 * stepSize * dTheta2_2)))) / (l2 * (2 * m1 + m2 - m2 * cos(2 * (y1[i] + 0.5 * stepSize * dTheta1_2) - 2 * (y2[i] + 0.5 * stepSize * dTheta2_2))));
//k4
double dTheta1_4 = y3[i] + stepSize * dTheta1_3;
double dOmega1_4 = (-g * (2 * m1 + m2) * sin(y1[i] + stepSize * dTheta1_3) - m2 * g * sin((y1[i] + stepSize * dTheta1_3) - 2 * (y2[i] + stepSize * dTheta2_3)) - 2 * sin((y1[i] + stepSize * dTheta1_3) - (y2[i] + stepSize * dTheta2_3)) * m2 * (pow(y4[i] + stepSize * dOmega2_3, 2) * l2 + pow(y3[i] + stepSize * dOmega1_3, 2) * l1 * cos((y1[i] + stepSize * dTheta1_3) - (y2[i] + stepSize * dTheta2_3)))) / (l1 * (2 * m1 + m2 - m2 * cos(2 * (y1[i] + stepSize * dTheta1_3) - 2 * (y2[i] + stepSize * dTheta2_3))));
double dTheta2_4 = y4[i] + stepSize * dTheta2_3;
double dOmega2_4 = (2 * sin((y1[i] + stepSize * dTheta1_3) - (y2[i] + stepSize * dTheta2_3)) * (pow(y3[i] + stepSize * dOmega1_3, 2) * l1 * (m1 + m2) + g * (m1 + m2) * cos(y1[i] + stepSize * dTheta1_3) + pow(y4[i] + stepSize * dOmega2_3, 2) * l2 * m2 * cos((y1[i] + stepSize * dTheta1_3) - (y2[i] + stepSize * dTheta2_3)))) / (l2 * (2 * m1 + m2 - m2 * cos(2 * (y1[i] + stepSize * dTheta1_3) - 2 * (y2[i] + stepSize * dTheta2_3))));
double theta1New = y1[i] + (stepSize / 6.0) * (dTheta1_1 + 2 * dTheta1_2 + 2 * dTheta1_3 + dTheta1_4);
double omega1New = y3[i] + (stepSize / 6.0) * (dOmega1_1 + 2 * dOmega1_2 + 2 * dOmega1_3 + dOmega1_4);
double theta2New = y2[i] + (stepSize / 6.0) * (dTheta2_1 + 2 * dTheta2_2 + 2 * dTheta2_3 + dTheta2_4);
double omega2New = y4[i] + (stepSize / 6.0) * (dOmega2_1 + 2 * dOmega2_2 + 2 * dOmega2_3 + dOmega2_4);
// updating y arrays
y1[i + 1] = theta1New;
y2[i + 1] = theta2New;
y3[i + 1] = omega1New;
y4[i + 1] = omega2New;
}
return make_tuple(y1, y2, t);
}
int main() {
//open parameters.txt, put data into a vector
ifstream fin("parameters.txt");
vector<double> data;
int element;
while (fin >> element) {
data.push_back(element);
}
//define tspan
vector<double> tspan(2);
tspan[0] = 0.0;
tspan[1] = 10.0;
//define stepSize
double stepSize;
stepSize = data[6];
//define range
int const range = 1000;
//define other constants
double l1 = data[2];
double l2 = data[3];
//get y1, y2, t from RK4 function
auto temp = RK4();
vector<double> y1 = get<0>(temp);
vector<double> y2 = get<1>(temp);
vector<double> t = get<2>(temp);
double x_1[range], y_1[range], x_2[range], y_2[range];
//define x_1, x_2, y_1, y_2
for (int i = 0; i < range; i++) {
x_1[i] = { sin(y1[i]) * l1 };
y_1[i] = { -cos(y1[i]) * l1 };
x_2[i] = { sin(y1[i]) * l1 + sin(y2[i]) * l2 };
y_2[i] = { -cos(y1[i]) * l1 - cos(y2[i]) * l2 };
}
//writing x,y positions at time t to output.txt
ofstream myfile;
myfile.open("C:\mydirectory\output.txt");
if (myfile.is_open()) {
myfile << "t: " << endl;
for (int i = 0; i < range; i++) {
myfile << t[i] << " ";
}
cout << endl;
myfile << "x_1: " << endl;
for (int i = 0; i < range; i++) {
myfile << x_1[i] << " ";
}
cout << endl;
myfile << "y_1: " << endl;
for (int i = 0; i < range; i++) {
myfile << y_1[i] << " ";
}
cout << endl;
myfile << "x_2: " << endl;
for (int i = 0; i < range; i++) {
myfile << x_2[i] << " ";
}
cout << endl;
myfile << "y_2: " << endl;
for (int i = 0; i < range; i++) {
myfile << y_2[i] << " ";
}
cout << endl;
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
当我尝试构建和运行程序(在Visual Studio中)时，我得到这个错误:
线程0x22c0已经退出，代码0 (0x0)。调试断言失败!
表达式:vector下标out of range
有关程序如何导致断言的信息
程序已退出，代码为3 (0x3)。
当我尝试调试程序时，我得到:
异常抛出c++ coursework new.exe触发了一个断点
有什么问题吗?
在这部分
for (int i = 0; i < range; i++) {
x_1[i] = { sin(y1[i]) * l1 };
y_1[i] = { -cos(y1[i]) * l1 };
x_2[i] = { sin(y1[i]) * l1 + sin(y2[i]) * l2 };
y_2[i] = { -cos(y1[i]) * l1 - cos(y2[i]) * l2 };
}
1000 (=range)个元素将从y1和y2中读取，而不管它们的实际大小。
这可能导致访问超出范围。
您应该将range设置为它们的元素数量。
由于可变长度数组不在标准c++中，您应该使用std::vector来代替数组。
行
int const range = 1000;
应删除，
行double x_1[range], y_1[range], x_2[range], y_2[range];
应该
int const range = static_cast<int>(y1.size());
std::vector<double> x_1(range), y_1(range), x_2(range), y_2(range);
一般来说，这段代码中有许多可能的错误原因，没有显式检查。例如:
你必须检查前提条件。例如:
while (fin >> element) {
data.push_back(element);
}
// add some checks
if (data.size() < 8) { ... precondition failed. handle ... }
和
stepSize = data[6];
if (stepSize too small or == 0) { .. precondition failed. handle ... }
幂函数pow()的基数也不能为负。
你还做了很多除法而没有检查除法是否为0——这也可能导致错误。