How to parse a string to an int in C++?

Question

What\'s the C++ way of parsing a string (given as char *) into an int? Robust and clear error handling is a plus (instead of returning zero).

Answer 1

I know three ways of converting String into int:

Either use stoi(String to int) function or just go with Stringstream, the third way to go individual conversion, Code is below:

1st Method

std::string s1 = "4533";
std::string s2 = "3.010101";
std::string s3 = "31337 with some string";

int myint1 = std::stoi(s1);
int myint2 = std::stoi(s2);
int myint3 = std::stoi(s3);

std::cout <<  s1 <<"=" << myint1 << '\n';
std::cout <<  s2 <<"=" << myint2 << '\n';
std::cout <<  s3 <<"=" << myint3 << '\n';

2nd Method

#include 
#include 
#include 
#include 
using namespace std;


int StringToInteger(string NumberAsString)
{
    int NumberAsInteger;
    stringstream ss;
    ss << NumberAsString;
    ss >> NumberAsInteger;
    return NumberAsInteger;
}
int main()
{
    string NumberAsString;
    cin >> NumberAsString;
    cout << StringToInteger(NumberAsString) << endl;
    return 0;
} 

3rd Method - but not for an individual conversion

std::string str4 = "453";
int i = 0, in=0; // 453 as on
for ( i = 0; i < str4.length(); i++)
{

    in = str4[i];
    cout <