自定义字符串排序会导致分段错误

我正在解决一个问题，在这个问题中，给你一组字符串格式的数字，你必须以这样的方式将它们连接起来，结果是尽可能多的数字。例如：

输入：6 61 68

输出：68661

因此，我使用带有std::sort的自定义分类器对字符串进行排序，当使用.at()访问字符串时，我会遇到奇怪的随机分段错误

我正在使用此命令运行代码

g++ -Wextra -Wall -pipe -O2 -std=c++14 largest_number_problem.cpp -lm && ./a.out

g++ --version的输出

g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0

输出为：

terminate called after throwing an instance of 'std::out_of_range'
what():  basic_string::at: __n (which is 0) >= this->size() (which is 0)
Aborted (core dumped)

注意：数组中没有长度为零的字符串。看看代码。

有时我会得到：无法访问0x0位置的内存。

我的代码：

#include "bits/stdc++.h"
using namespace std;
bool sortNos(const string &s1, const string &s2)
{
int i1 = 0, i2 = 0;
int n1 = s1.size(), n2 = s2.size();
bool result = 0;

while (i1 < n1 && i2 < n2)
{
if (s1.at(i1) != s2.at(i2))
{
result = s1.at(i1) > s2.at(i2);
return result;
}
i1++;
i2++;
}
if (i1 == n1 && i2 == n2)
{
// strings are equal
return 1;
}
if (i1 == n1)
{
result = s1.at(0) > s2.at(i2);
}
else if (i2 == n2)
{
result = s2.at(0) < s1.at(i1);
}
return result;
}
string largest_number(vector<string> &a)
{
sort(a.begin(), a.end(), &sortNos);
std::stringstream ret;
for (size_t i = 0; i < a.size(); i++)
{
ret << a[i];
}
string result;
ret >> result;
return result;
}
void test()
{
vector<string> a;
a.push_back("2");
a.push_back("8");
a.push_back("2");
a.push_back("3");
a.push_back("6");
a.push_back("4");
a.push_back("1");
a.push_back("1");
a.push_back("10");
a.push_back("6");
a.push_back("3");
a.push_back("3");
a.push_back("6");
a.push_back("1");
a.push_back("3");
a.push_back("8");
a.push_back("4");
a.push_back("6");
a.push_back("1");
a.push_back("10");
a.push_back("8");
a.push_back("4");
a.push_back("10");
a.push_back("4");
a.push_back("1");
a.push_back("3");
a.push_back("2");
a.push_back("3");
a.push_back("2");
a.push_back("6");
a.push_back("1");
a.push_back("5");
a.push_back("2");
a.push_back("9");
a.push_back("8");
a.push_back("5");
a.push_back("10");
a.push_back("8");
a.push_back("7");
a.push_back("9");
a.push_back("6");
a.push_back("4");
a.push_back("2");
a.push_back("6");
a.push_back("3");
a.push_back("8");
a.push_back("8");
a.push_back("9");
a.push_back("8");
a.push_back("2");
a.push_back("9");
a.push_back("10");
a.push_back("3");
a.push_back("10");
a.push_back("7");
a.push_back("5");
a.push_back("7");
a.push_back("1");
a.push_back("7");
a.push_back("5");
a.push_back("1");
a.push_back("4");
a.push_back("7");
a.push_back("6");
a.push_back("1");
a.push_back("10");
a.push_back("5");
a.push_back("4");
a.push_back("8");
a.push_back("4");
a.push_back("2");
a.push_back("7");
a.push_back("8");
a.push_back("1");
a.push_back("1");
a.push_back("7");
a.push_back("4");
a.push_back("1");
a.push_back("1");
a.push_back("9");
a.push_back("8");
a.push_back("6");
a.push_back("5");
a.push_back("9");
a.push_back("9");
a.push_back("3");
a.push_back("7");
a.push_back("6");
a.push_back("3");
a.push_back("10");
a.push_back("8");
a.push_back("10");
a.push_back("7");
a.push_back("2");
a.push_back("5");
a.push_back("1");
a.push_back("1");
a.push_back("9");
a.push_back("9");
a.push_back("5");
largest_number(a);
}
int main()
{
test();
return 0;
}