id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
6852	lexical_cast: warning: ISO C++ does not support the ‘%lg’ gnu_printf format	peter@…	Antony Polukhin	"The following code produces a warning if compiled with GCC (4.7.0) and -Wall -std=c++98 -pedantic:

{{{
include <boost/lexical_cast.hpp>

int main()
{
    boost::lexical_cast<std::string>(double(4.2));
    return 0;
}
}}}

{{{
boost_1_49_0/include/boost/lexical_cast.hpp:1297:17: warning: ISO C++ does not support the ‘%lg’ gnu_printf format [-Wformat]
}}}


With regard to the length modifier, the printf(3) man page (RHEL 6.2) states:
{{{
       l      (ell) A following integer conversion corresponds to a  long  int
              or  unsigned long int argument, or a following n conversion cor-
              responds to a pointer to a long int argument, or a  following  c
              conversion  corresponds  to  a wint_t argument, or a following s
              conversion corresponds to a pointer to wchar_t argument.
}}}

With regard to the conversion specifier:
{{{
       g, G   The  double argument is converted in style f or e (or F or E for
              G conversions).  The precision specifies the number of  signifi-
              cant  digits.   If the precision is missing, 6 digits are given;
              if the precision is zero, it is treated as 1.  Style e  is  used
              if  the  exponent from its conversion is less than -4 or greater
              than or equal to the precision.  Trailing zeros are removed from
              the  fractional part of the result; a decimal point appears only
              if it is followed by at least one digit.
}}}

So the correct printf format for double is ""%g"".

(Maybe this is different on non-GNU systems?)"	Bugs	closed	To Be Determined	lexical_cast	Boost 1.49.0	Cosmetic	fixed