Following the issue #1227, this PR is making the function atof_locale_c much more pedantic and rejects any number that do not match a strict syntax such as [+-]0.12E[+-]34 or 12.34. A regular expression is used for that purpose (they have been introduced in C++11).

1. New exception InvalidNumer

A new exception class JSBSim::InvalidNumber has been created which inherits from JSBSim::BaseException. Since the former is defined in input_output/string_utilities.h and the latter in FGJSBBase.h, it was no longer possible that FGJSBBase.h includes string_utilities.h because that was creating a mutual dependence that compilers complain about. Actually FGJSBBase.h does not need to include string_utilities.h so the corresponding #include has simply been removed from FGJSBBase.h. As a consequence, a number of source files have been modified to explicitly include string_utilities.h.

2. atof_locale_c pedantry

The function is_number will now be much more pedantic and will basically be a function that checks that atof_locale_c succeeds.

All the occurrences of the following code:

double a_value;
std::string a_string;

if (is_number(a_string)) {
  a_value = atof_locale_c(trim(a_string));
} else {
  // Error management
}

have been replaced by

double a_value;
std::string a_string;

try {
  a_value = atof_locale_c(trim(a_string));
} catch (InvalidNumber& e) {
  // Error management
}

The problem was that both is_number and strtod_l have a relaxed interpretation of what a valid number syntax is. For example strtod_l("1.3.2", nullptr, numeric_c.Locale); returns 1.3 and the strings x and . return 0.0. In addition the strings 1.3.2 and . are considered valid numbers by is_number although it rejects x. The regular expression will allow rejecting these strings as invalid.

Once this PR will be merged, all the validation and conversion work will be made by atof_locale_c which is now extremely pedantic. Also since the PR #799, atof_locale_c uses the locale "C" for numerical value whatever is the setting of LC_NUMERIC.

3. Removal of calls to atof

Most of the calls to atof have been replaced by atof_locale_c. The remaining calls to atof are all located in simger/props/props.cxx:

4. Remaining calls to strto functions

Some calls to the standard library functions starting with strto (such as strtol, strtod, ...) remain.

The following call to strtod is made in SGPropertyNode::getLongValue:

The following call to strtoul is made in simgear/xml/xmlparse.c

Conclusion

• This PR is making the conversion from string to double much more pedantic.
• Most of the calls to atof have been removed and replaced by atof_locale_c. For the record, the behavior of atof depends on the environment variable LC_NUMERIC.
• Some calls to the atof and strto functions remain but they are located in functions which we do not use.
  • Most of these calls are located in simgear/props/props.cxx and I am reluctant to use atof_locale_c in this piece of code. If we want to be super safe, I'd rather remove the aforementioned functions from SGPropertyNode since we are not using them anyway.