How to check for overflow converting char*[] to unsigned short

Question

I am trying to convert a user input into unsigned short:

int main(int argc, char *argv[])
{
    unsigned short tl;
    tl = (unsigned short) strtoul(argv[2], NULL, 0);
}

For example: a user input of "555555" overflows and becomes 31267.

How can I stop/check for overflows while also trying to convert the input? What is the most efficient and effective way to stop that from happening?

Many thanks in advance.

Answer 1

If you look at the documentation of strtoul on cppreference.com

If the converted value falls out of range of corresponding return type, range error occurs and ULONG_MAX or ULLONG_MAX is returned.

You should be able to detect this by checking errno for ERANGE .

Something like this should therefore work for you:

#include <limits>
#include <cerror>

auto n = strtoul(argv[2], NULL, 0);
if (errno == ERANGE || n > std::numeric_limits<unsigned short>::max()) {
  // Handle overflow
}
else {
  // Do something
}