search

boostorg / lexical_cast

General literal text conversions, such as an int represented as a string, or vice versa
https://boost.org/libs/lexical_cast
34 stars 58 forks source link

lexical_cast<unsigned> succeeds for negative numbers #17

Closed petersohn closed 8 years ago

petersohn commented 8 years ago

Attempting to convert a string containing a number that is too big for an int but fits into unsigned throws a bad_lexical_cast, as expected. However, attempting to convert a string with a negative number to unsigned succeeds, although it should also throw.

See example here: http://coliru.stacked-crooked.com/a/73d91c38e5eaa3da

apolukhin commented 8 years ago

That's a known and sad "feature" of the C:

boost::lexical_cast has the behavior of std::stringstream, which uses num_get functions of std::locale to convert numbers. If we look at the Programming languages — C++, we'll see, that num_get uses the rules of scanf for conversions. And in the C99 standard for unsigned input value minus sign is optional, so if a negative number is read, no errors will arise and the result will be the two's complement.