Cannot convert from string to int using stoi - c++

Question

In my program first I read a file into a vector of strings called rosterList:
100
95
0
-1
110
80
90
-1
120
80
75
-1
130
60
55
-1
This step is successful. My goal is to create a vector of Student objects using the data above. Constructor accepts 3 strings as parameters:
Student::Student(string id,string g1,string g2)
To do that, the program loops through this vector of strings line by line, if the line converted to integer is greater or equal to 100, it is an id, then dynamically create a new Student object by passing the id (current line) and the next 2 lines as parameters, and add the object to the vector studentRecords
for (vector<string>::iterator it = rosterList.begin(); it<rosterList.end();it++){
if(stoi(*it)>=100 || it == rosterList.begin()){ // error
studentRecords.push_back(
Student(*it,*(it+1),*(it+2)) // dynamically push
);
}
}
And there is a dynamic error:
libc++abi.dylib: terminating with uncaught exception of type
std::invalid_argument: stoi: no conversion
I looked it up online, the error comes from stoi not be able to convert. Where in the program goes wrong?

Answer 1

Either you have to read your file correctly....or
If you are not confident on file data, do a validation for numeric content.
Below is code sample.
Any junk that you read other than numeric content in your file will cause failure.
Below code compiles and for your idea. You can optimize it.
#include <iostream>
#include <cstring>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
std::vector<string> rosterList;
bool is_numeric(string strin)
{
char const *str = strin.c_str();
return all_of(str, str+strlen(str),
[](unsigned char c) { return ::isdigit(c); });
}
int main(int argc, char *argv[])
{
rosterList.push_back("100");
rosterList.push_back(" ");
rosterList.push_back("140");
rosterList.push_back("180");
for (vector<string>::iterator it = rosterList.begin(); it<rosterList.end();it++){
if(is_numeric(*it) && (stoi(*it)>=100 || it == rosterList.begin())){ // error
std::cout<<stoi(*it)<<std::endl;
}
}
}

Answer 2

One problem I see in your code is that you're accessing it+1 and it+2 also when it is the last 2 positions of the vector. This will try to access a pointer that doesn't exist as this points to after rosterList.end().
You will have to test if it+1 and it+2 are < than rosterList.end() before using them.