STL bitset crash on to_ulong()

This is a discussion on STL bitset crash on to_ulong() within the C++ Programming forums, part of the General Programming Boards category; guys i got a small problem, my program to crashes with a Code: std::overflow_error the following code causes it at ...

  1. #1
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    Question 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
    Last edited by symbiote; 01-12-2009 at 08:25 AM.

  2. #2
    C++ Witch laserlight's Avatar
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    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.
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  3. #3
    The larch
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    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).
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
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  4. #4
    Cat without Hat CornedBee's Avatar
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    Is your unsigned long type even 64 bits wide?
    All the buzzt!
    CornedBee

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  5. #5
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    thanks i think i get it.

    i'm using vs 2005. i thought it was supposed to be 64 bits. hmm

  6. #6
    Cat without Hat CornedBee's Avatar
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    MS doesn't make long 64 bits under any circumstance due to compatibility concerns.
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