I am having an issue with the getline function [duplicate] - c++

Question

This question already has answers here:
cin and getline skipping input [duplicate]
(4 answers)
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 21 days ago.
#include <iostream>
using namespace std;
int main(){
//set variables
string name1;string name2;string name3;string n1;string n2;string n3;
int age1; int age2; int age3;
//get names and ages
cout << "Who Is The First Student?"<< endl;
getline(cin, name1); //name 1
cout << "What is " << name1<< "'s Age?"<< endl;
cin >> age1; // age 1
cout << "Who Is The Second Student?"<< endl;
getline(cin, name2); //name 2
cout << "What is " << name2<< "'s Age?"<< endl;
cin >> age2; //age 2
cout << "Who Is The Third Student?"<< endl;
getline(cin, name3); // name 3
cout << "What is " << name3<< "'s Age?"<< endl;
cin >> age3; //age 3
// gets modified names
n1 = name1.substr(2, name1.size() -3);
n2 = name2.substr(2, name2.size() -3);
n3 = name3.substr(2, name3.size()-3);
// Output formatting
cout << "Name Age Modified"<<endl;
cout << name1<< " "<<age1<<" "<<n1<<endl;
cout << name2<< " "<<age2<<" "<<n2<<endl;
cout << name3<< " "<<age3<<" "<<n3<<endl;
return 0;
}
The output asks the first question which is for the name of the first student but it outputs as this:
Who Is The First Student?-
John Doe-
What is John's Age?-
19-
Who Is The Second Student?-
What is 's Age?-
It is skipping the user input of the second student's name and instantly asking for the age but I don't know why this is happening, is there something wrong with my code or do I have the formatting incorrect? I believe that I used the getline function correctly but I may be incorrect and unaware of it being skipped over by a more important function.

Answer 1

The std::string::substr() man page says this about the exception you are seeing:
Parameters
pos - position of the first character to include
count - length of the substring
Exceptions
[throws] std::out_of_range if pos > size()

Answer 2

The main problem of the program is that the operator >> reads only one word.
That is for example in these statements
cout << "Who Is The First Student?"<< endl;
cin >> name1; //name 1
You entered a string that contains two words "John Doe". But the operator >> reads only the first word "Jphn" in the variable name1.
So in the next input statement
cout << "What is " << name1<< "'s Age?"<< endl;
cin >> age1; // age 1
an error occurred because instead of a number the input buffer contains the word "Doe".
So as a result the variables name1, name2, and name3 do not contain what you are expecting. And these statements
n1 = name1.substr(2, name1.size()-3);
n2 = name2.substr(2, name2.size()-3);
n3 = name3.substr(2, name3.size()-3);
produce the run-time error.
Instead of the operator >> you should use standard function std::getline.
Here is a demonstration program based on the code of your program that shows what is the reason of the error
#include <iostream>
#include <string>
int main()
{
std::string name1, name2;
int age1;
//get names and ages
std::cout << "Input 3 Names Below:" << std::endl;
std::cout << "Who Is The First Student?" << std::endl;
std::cin >> name1; //name 1
std::cout << "What is " << name1 << "'s Age?" << std::endl;
std::cin >> age1; // age 1
std::cout << "Who Is The Second Student?" << std::endl;
std::cin >> name2; //name 2
std::cout << "name1 = " << name1 << '\n';
std::cout << "name2 = " << name2 << '\n';
}
The program output is
Input 3 Names Below:
Who Is The First Student?
John Doe
What is John's Age?
Who Is The Second Student?
name1 = John
name2 =
As you can see due to the error of reading a data in the variable age1 (the buffer contains the string "Doe") the object name2 is empty. So if you will use it in this statement
n2 = name2.substr(2, name2.size()-3);
then the runtime error will occur.
Here is another demonstration program that shows how the standard function std::getline can be used in your program.
#include <iostream>
#include <string>
#include <limits>
int main()
{
std::string name1, name2, name3;
int age1, age2, age3;
//get names and ages
std::cout << "Input 3 Names Below:" << std::endl;
std::cout << "Who Is The First Student?" << std::endl;
std::getline( std::cin, name1 ); //name 1
std::cout << "What is " << name1 << "'s Age?" << std::endl;
std::cin >> age1; // age 1
std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
std::cout << "Who Is The Second Student?" << std::endl;
std::getline( std::cin, name2 ); //name 2
std::cout << "What is " << name2 << "'s Age?" << std::endl;
std::cin >> age2; //age 2
std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
std::cout << "Who Is The Third Student?" << std::endl;
std::getline( std::cin, name3 ); // name 3
std::cout << "What is " << name3 << "'s Age?" << std::endl;
std::cin >> age3;
std::cout << "name1 = " << name1 << '\n';
std::cout << "name2 = " << name2 << '\n';
std::cout << "name3 = " << name3 << '\n';
}
The program output is
Input 3 Names Below:
Who Is The First Student?
John Dow
What is John Dow's Age?
20
Who Is The Second Student?
Mary Poppins
What is Mary Poppins's Age?
21
Who Is The Third Student?
Bob Fisher
What is Bob Fisher's Age?
25
name1 = John Dow
name2 = Mary Poppins
name3 = Bob Fisher