How can I convert a std::string to int?

Question

Just have a quick question. I\'ve looked around the internet quite a bit and I\'ve found a few solutions but none of them have worked yet. Looking at converting a string to

Answer 1

Well, lot of answers, lot of possibilities. What I am missing here is some universal method that converts a string to different C++ integral types (short, int, long, bool, ...). I came up with following solution:

#include
#include
#include
#include

using namespace std;

template
T toIntegralType(const string &str) {
    static_assert(is_integral::value, "Integral type required.");
    T ret;
    stringstream ss(str);
    ss >> ret;
    if ( to_string(ret) != str)
        throw invalid_argument("Can't convert " + str);
    return ret;
}

Here are examples of usage:

string str = "123";
int x = toIntegralType(str); // x = 123

str = "123a";
x = toIntegralType(str); // throws exception, because "123a" is not int

str = "1";
bool y = toIntegralType(str); // y is true
str = "0";
y = toIntegralType(str); // y is false
str = "00";
y = toIntegralType(str); // throws exception

Why not just use stringstream output operator to convert a string into an integral type? Here is the answer: Let's say a string contains a value that exceeds the limit for intended integral type. For examle, on Wndows 64 max int is 2147483647. Let's assign to a string a value max int + 1: string str = "2147483648". Now, when converting the string to an int:

stringstream ss(str);
int x;
ss >> x;

x becomes 2147483647, what is definitely an error: string "2147483648" was not supposed to be converted to the int 2147483647. The provided function toIntegralType spots such errors and throws exception.