urdfdom usage of std::stod is error-prone to changes in system locale

[traversaro]

The use in several parts of urdfdom of the function std::stod can be source of errors if the library is used together with other libraries (such as Qt) that change the system locale.

Slightly related, I assume (from all the ROS code using the library) the correct way of encoding floating point numbers as strings in the URDF file format is the one defined by the "C" standard locale, but this is not actually documented anywhere (see robotology/idyntree#288 (comment)).

Downstream issue: robotology/idyntree#288
Similar SDFormat issue: https://bitbucket.org/osrf/sdformat/issues/60

[traversaro]

This is not directly related to urdfdom, but apparently a lot of custom URDF/SDF parser available in existing libraries suffer the same problem.

I just checked and I easily found several examples:

• DART https://github.com/dartsim/dart/blob/52bbd15f8d01e97ed4bdf91b7731daffb4929de7/dart/utils/XmlHelpers.cpp#L167 (lexical_cast is also affected, http://stackoverflow.com/questions/18980423/locale-invariant-guarantee-of-boostlexical-cast , cc @jslee02 )
• Bullet https://github.com/bulletphysics/bullet3/blob/79d24db60f2c916ffcdaf8b074be622e2e5bc609/examples/Importers/ImportURDFDemo/urdfLexicalCast.h#L7
• Drake https://github.com/RobotLocomotion/drake/blob/4532d9460627535e5feb7d0f19ce951b35b19f95/drake/multibody/parsers/xml_util.cc#L70
• Simbody https://github.com/simbody/simbody/blob/3469006e99a94e9a3c7201a5308d298d20acf07f/SimTKcommon/include/SimTKcommon/internal/String.h#L395

[traversaro]

cc @liesrock this is the issue I was mentioning today that is also affecting RBDL indirectly.

[liesrock]

thanks @traversaro, I cc @alaurenzi that can be also interested.

[traversaro]

Fixed by #105 .