boost::lexical_cast<float>(".") returns 0 instead of throwing

[Bruce Merry <bmerry@…>]

The attached program reports

boost::lexical_cast<float>(".") returns 0

when it should report an exception. According to the lexical_cast docs, lexical_cast<float>(string) is supposed to be equivalent to

• using stream extraction, which in turn is defined in terms of
• num_get on the numeric facet, which is defined in terms of
• strtold in the C standard, which requires
• "a non-empty sequence of decimal digits, optionally containing a decimal-point character"

strtold also refers to the grammar for a floating-point literal, which is pretty clear that either the part before or the part after the decimal point has to be non-empty. Compiler is MSVC 2010 SP1. I haven't messed around with locales at all so it's whatever the default is for an English install of Windows 7.

This works with Boost 1.46 under GCC 4.6 - I'm guessing because 1.46 left parsing of float strings to operator>>.

[Bruce Merry <bmerry@…>]

Ack, the attachment went through twice. lc.cpp and lc.2.cpp are the same file.

[Antony Polukhin]

(In [78111]) Fixes #6812 (now converting "." to float type throws bad_lexical_cast)

[Antony Polukhin]

(In [78211]) Merge from trunk:

• fixed #6812 (now converting "." to float type throws bad_lexical_cast)