Invalid "negative strings" are treated as numbers

[morinim]

Inside:

inline bool parser::is_number(std::string const& arg) const
{
   std::istringstream istr(arg);
   double number;
   istr >> number;
   return !(istr.fail() || istr.bad());
}

stream extraction succeeds when it can parse a numeric prefix. It doesn't require the entire string to be numeric.

For example:

• -1abc -> parses numeric prefix -1;
• -1.2.3 -> parses numeric prefix -1.2.

and is_number() returns true. Then

inline bool parser::is_option(std::string const& arg) const
{
   assert(0 != arg.size());
   if (is_number(arg))
      return false;
   ...

returns false, causing these arguments to be stored as positional values:

const char* argv[] = { "-1abc" };
argh::parser cmdl(1, argv);

Actual:

cmdl.pos_args().size() == 1
cmdl.flags().empty()

Expected:

cmdl["1abc"] == true

This can also alter subsequent parsing. Given a registered parameter --output -1abc, -1abc may be consumed as output value instead of being recognised as another option.

[morinim]

A possible fix is to require the complete argument, apart from trailing whitespace, to be consumed:

inline bool parser::is_number(std::string const& arg) const
{
   std::istringstream istr(arg);
   double number;

   if (!(istr >> number))
      return false;

   istr >> std::ws;
   return istr.eof();
}

A regression test could cover both malformed and valid negative numbers:

TEST_CASE("Numeric arguments must be complete numbers")
{
   const char* argv[] = {"-1abc", "-1.2.3", "-1", "-0.4", "-1.3e-2"};

   argh::parser cmdl(sizeof(argv) / sizeof(argv[0]), argv);

   CHECK(cmdl["1abc"]);
   CHECK(cmdl["1.2.3"]);

   CHECK(cmdl.pos_args() == std::vector<std::string>{"-1", "-0.4", "-1.3e-2"});
}

Thanks for creating and maintaining argh. I really like its simplicity and I hope this report is helpful.