CODEWITHSUNDEEP
c++string-conversion
Nirket Shivantrepadi
Nirket Shivantrepadi

Reputation: 93

C++ std::stoul not throwing exception

I have a function to check if a string is a valid unsigned int:

unsigned long int getNum(std::string s, int base)
{
    unsigned int n;
    try
    {
        n = std::stoul(s, nullptr, base);
        std::cout << errno << '\n';
        if (errno != 0)
        {
            std::cout << "ERROR" << '\n';
        }
    }
    catch (std::exception & e)
    {
        throw std::invalid_argument("Value is too big");
    }
    return n;
}

However when I enter a value such as 0xfffffffff (9 f's), errno is still 0 (and no exception is thrown). Why is this the case?

Upvotes: 7

Views: 8474

Answers (1)

P.W
P.W

Reputation: 26800

Let's see what happens when you assign 0xfffffffff (9 f's) to an unsigned int on an 64-bit machine. 

#include <iostream>

int main(){

    unsigned int n = 0xfffffffff; //decimal value 68719476735
    std::cout << n << '\n';

}

The implicit conversion will result in a warning by the compiler but will not cause an exception.

The result type of stoul is unsigned long which on 64-bit machine is big enough to hold 0xfffffffff, so there will be no exception.

Upvotes: 6

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