为什么在这里使用stoi会给我错误？

Question

我正在尝试读取输入的第二行和第三行，其中这两行的第一个数字是数组的长度（该行中的数字数目（不包括空格和第一个数字））。我想将数组的长度存储在一个单独的数组中，并将这些行上的其余数字打印到STDOUT。我目前有以下代码，但收到与stoi函数有关的错误。

#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <sstream>
using namespace std;


int main() {
    int numarr;
    int numqueries;
    string line;
    char chars;

    scanf("%d %d",&numarr,&numqueries);
    vector<string> lengths = vector<string>(numarr);
    vector<int> arrays = vector<int>(numarr);
    vector<int> queries = vector<int>(numqueries); 
    int lq = 0;
    while(getline(cin,line) && lq <= numarr){
        stringstream iss(line);
        string wd;
        string dd;
        int cnt = 1;
        while(cnt == 1 || (iss >> wd && cnt < stoi(lengths[cnt-1]))){
            if(cnt == 1){
                lengths[cnt-1] = wd;
                cout << "first";
                cnt++;
            }else{
            cout << wd;
            cnt++;  
            }   
        }
        lq += 1;
    }


    return 0;
}

错误输出：

terminate called after throwing an instance of 'std::invalid_argument'

  what():  stoi

Reading symbols from Solution...done.

[New LWP 499362]

[Thread debugging using libthread_db enabled]

Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Core was generated by `./Solution'.

Program terminated with signal SIGABRT, Aborted.

#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51

To enable execution of this file add

    add-auto-load-safe-path /usr/local/lib64/libstdc++.so.6.0.25-gdb.py

line to your configuration file "//.gdbinit".

To completely disable this security protection add

    set auto-load safe-path /

line to your configuration file "//.gdbinit".

For more information about this security protection see the

"Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:

    info "(gdb)Auto-loading safe path"

示例输入：

2 2
3 1 5 4
5 1 2 8 9 3
0 1
1 3