c++判断线段是否相交

判断线段是否相交可以使用叉积或者向量。具体实现可以参考以下代码：

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    double x, y;
} Point;

typedef struct {
    Point p1, p2;
} Line;

double cross_product(Point a, Point b) {
    return a.x * b.y - b.x * a.y;
}

int is_intersected(Line L1, Line L2) {
    double c1 = cross_product((Point){L1.p1.x - L2.p1.x, L1.p1.y - L2.p1.y}, (Point){L2.p2.x - L2.p1.x, L2.p2.y - L2.p1.y});
    double c2 = cross_product((Point){L1.p2.x - L2.p1.x, L1.p2.y - L2.p1.y}, (Point){L2.p2.x - L2.p1.x, L2.p2.y - L2.p1.y});
    double c3 = cross_product((Point){L2.p1.x - L1.p1.x, L2.p1.y - L1.p1.y}, (Point){L1.p2.x - L1.p1.x, L1.p2.y - L1.p1.y});
    double c4 = cross_product((Point){L2.p2.x - L1.p1.x, L2.p2.y - L1.p1.y}, (Point){L1.p2.x - L1.p1.x, L1.p2.y - L1.p1.y});

    if (c1 * c2 < 0 && c3 * c4 < 0) {
        return 1;
    } else {
        return 0;
    }
}

int main() {
    Line L1 = {{0, 0}, {1, 1}}, L2 = {{0, 1}, {1, 0}};
    if (is_intersected(L1, L2)) {
        printf("Line segments intersect.\n");
    } else {
        printf("Line segments don't intersect.\n");
    }
    return 0;
}

该代码中使用了叉积的方法来判断两条线段是否相交。如果叉积小于零，则表示两条线段相交，否则不相交。