给出以下简单使用Boost.Program_Options：
boost::program_options::options_description options("Options");
options.add_options()
("my_bool_flag,b",boost::program_options::value<bool>(),"Sample boolean switch)")
;
什么命令行参数将评估为false,以及什么是真的？
(即,假定程序命名为“foo”,并在命令行上执行：
foo -b？
…问号是一些其他文字的占位符：什么是所有可能的文本选项,将正确评估为false,以及真正的？)
解决方法
看看$(BOOST_ROOT)/libs/program_options/src/value_semantic.cpp你可以找到：
/* Validates bool value.
Any of "1","true","yes","on" will be converted to "1".<br>
Any of "0","false","no","off" will be converted to "0".<br>
Case is ignored. The 'xs' vector can either be empty,in which
case the value is 'true',or can contain explicit value.
*/
BOOST_PROGRAM_OPTIONS_DECL void validate(any& v,const vector<string>& xs,bool*,int)
{
check_first_occurrence(v);
string s(get_single_string(xs,true));
for (size_t i = 0; i < s.size(); ++i)
s[i] = char(tolower(s[i]));
if (s.empty() || s == "on" || s == "yes" || s == "1" || s == "true")
v = any(true);
else if (s == "off" || s == "no" || s == "0" || s == "false")
v = any(false);
else
boost::throw_exception(invalid_bool_value(s));
}
