Thread: STL bitset crash on to_ulong()

guys i got a small problem,

my program to crashes with a

Code:

std::overflow_error

the following code causes it at the second statement:

Code:

#include <bitset>

int main()
{
	bitset<64> x( string("0000000000000000000000000000010001101000011001010110110001101100") ) ;
	
	unsigned long y = x.to_ulong() ;

	getchar() ;
	return 0 ;
}

no crash if i use the decimal value instead :

Code:

	bitset<64> x( 18931346540 ) ;

it doesn't make sense to me. could anyone explain?

thanks,
sym

unsigned long on your platform is probably a 32 bit integer. It appears to work in the second case because 18931346540 might be a (currently) non-standard integer literal of a type with greater range than unsigned long (e.g., unsigned long long or __int64), but is truncated.

Apparently the size of unsigned long is 32 bits. If the number is too large to convert bitset throws an exception.

In the second case the literal constant is just too large for unsigned long and 4 bytes of it just gets chopped away. The bitset won't be constructed with the value you pass (instead it will likely be 1751477356).

Is your unsigned long type even 64 bits wide?

MS doesn't make long 64 bits under any circumstance due to compatibility concerns.