#include <cinttypes>
#include <string>
#include <algorithm>
#include <iostream>
using namespace std;
uint64_t descendingOrder(uint64_t a)
{
string str = to_string(a);
sort(str.begin(),str.end(),[](unsigned char a , unsigned char b) { return a>b;});
cout<<"sorted string:" <<str<<endl;
cout<<"value :"<<strtol(str.c_str(),nullptr,10)<<endl;
return strtol(str.c_str(),nullptr,10);
}
int main()
{
descendingOrder(9223372036854775807L);
}
sorted string:9887777655433322200
value :9223372036854775807
Why are the sorted string:
and value:
are different? It seems like value:
took the original string somehow even after sorting. Where is the mistake? Is it UB?
Code: Online code
9887777655433322200 is out of range for a long
on your architecture.
That's why errno
gets set to ERANGE
and LONG_MAX
(which happens to be your input) is returned. Note that an implementation may also use LLONG_MIN
or LLONG_MIN
or even LONG_MIN
. You need to check errno
in order to know whether the conversion with strtol
worked.
If you used std::stol
you would have ended up with an std::out_of_range
exception instead. Whether you want to use exceptions is up to you, but meanwhile, use either std::strtoull
for unsigned long long
(and check errno
) or use std::stoull
(and keep possible exceptions in mind).
See [string.conversions]
in the C++ standard or the links above to cppreference.com for more information.