我把代码放在int main（）{}之外的分段错误

Question

第一个代码块工作，但第二个代码块没有，我不知道为什么。我在第二段代码中遇到了分段错误。

#include "Graph.h"
#include "Simple_window.h"
#include "std_lib_facilities_3.h"

using namespace Graph_lib;

Point t1(100,100);
Simple_window win(t1,700,700,"Calendar");

int main(){
    Vector_ref<Text> weekdays;
    vector<string> weekday = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

    for (int a = 0; a < weekday.size(); ++a){
        weekdays.push_back(new Text(Point(a*100+28,90), weekday[a]));
        weekdays[weekdays.size()-1].set_font_size(10);
        win.attach(weekdays[weekdays.size()-1]);
    }
}

以下代码给出了分段错误。

#include "Graph.h"
#include "Simple_window.h"
#include "std_lib_facilities_3.h"

using namespace Graph_lib;

Point t1(100,100);
Simple_window win(t1,700,700,"Calendar");

void draw_weekdays(){
    Vector_ref<Text> weekdays;
    vector<string> weekday = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

    for (int a = 0; a < weekday.size(); ++a){
        weekdays.push_back(new Text(Point(a*100 + 28, 90), weekday[a]));
        weekdays[weekdays.size()-1].set_font_size(10);
        win.attach(weekdays[weekdays.size()-1]);
    }
}

int main(){
    draw_weekdays();
}

我已将问题缩小到“win.attach（weekdays [weekdays.size（） - 1]）”这一行，但除此之外，我感到难过。