已知线段上某点与起点的距离，求该点的坐标

#include <iostream>

using namespace std;

// 2D Point
struct Vector2d
{
public:
    Vector2d()
    {
    }

    Vector2d(double dx, double dy)
    {
        x = dx;
        y = dy;
    }

    // 矢量赋值
    void set(double dx, double dy)
    {
        x = dx;
        y = dy;
    }

    // 矢量相加
    Vector2d operator + (const Vector2d& v) const
    {
        return Vector2d(x + v.x, y + v.y);
    }

    // 矢量相减
    Vector2d operator - (const Vector2d& v) const
    {
        return Vector2d(x - v.x, y - v.y);
    }

    //矢量数乘
    Vector2d Scalar(double c) const
    {
        return Vector2d(c*x, c*y);
    }

    // 矢量点积
    double Dot(const Vector2d& v) const
    {
        return x * v.x + y * v.y;
    }

    //向量的模
    double Mod() const
    {
        return sqrt(x * x + y * y);
    }

    double x, y;
};

void CalPointFromLineWithDistance(const Vector2d & O, const Vector2d & E, double d, Vector2d& P)
{
    Vector2d D = E - O; 
    double t = d / D.Mod();
    P = O + D.Scalar(t);
}

int main()
{
    Vector2d O(1.0, 2.4);
    Vector2d E(10.2, 11.5);
    double d = 5;
    Vector2d P;

    CalPointFromLineWithDistance(O, E, d, P);
    cout << "计算的点为：" << P.x<<'\t' << P.y << '\n'; 

    cout << "验算距离是否为"<<d<<"：" <<(P-O).Mod()<< '\n';
}