Motivation / Problem

Some (string) settings you want to validate before the setting is written as to prevent the user from entering something invalid. For example an empty client name. Now the (string) validation can only happen in the post set update, so there is no way to revert anymore. To implement that it would be nice not to have to worry about three types of strings coming from the settings: a C-string buffer, a heap allocated C-string and std::string.

For the media things a start has already been made with std::string, so this is just the continuation of that change.

Description

Everywhere where a C-string buffer or heap allocated C-string setting was used this is converted to std::string, along with some of the related logic for handling them. Arguably things might be pushed even further down the stacks, but that would balloon this PR so usually the bare minimum has been done.

Limitations

Empty digit separators are not possible anymore as they now fall back to the language's default.
The overall diff could be smaller if I chose to go back to SDT_STR etc, instead of SDT_SSTR. However, I chose not to do that so other people with patches get a compile time failure instead of a weird crash when it interprets char buffers as std::string or so.
Some variables, those that do not go over the network, I have generally not given an artificial limit as it's not really important how long e.g. a hostname is. It might now truncate it at a later stage in the application, but when the underlying code has been updated to fully use std::string that truncation problem should have gone away.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker