Environment helpers: function to set environment variable?

[aprotyas]

Feature request

It would be nice to have a way to set environment variables. I have at least one use-case in ros2/domain_bridge#60 (comment).

Feature description

A function that allows setting a named environment variable; essentially a dual of rcpputils::get_env_var.

Implementation considerations

It could be implemented exactly how rcpputils::get_env_var is implemented, by invoking the corresponding rcutils environment helper function.

One approach:

bool set_env_var(const char * env_var, const char * env_value)
{
  if (!rcutils_set_env(env_var, env_value)) {
    std::string err = rcutils_get_error_string().str;
    // Resetting the error state since error string has been extracted
    rcutils_reset_error();
    throw std::runtime_error(err);
  }
  return true;
}

[aprotyas]

I've already opened #150 with my own implementation, but if that needs changing, feel free to open a separate PR to close this issue.

[fujitatomoya]

this makes sense to me, i am good to go with this.