[ARROW-4128] [C++][DOCUMENTATION] Update style guide to reflect some more exceptions

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 0.12.0
• Component/s: C++, Documentation
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/15920
• Assignee: Micah Kornfield
• Reporter: Micah Kornfield
• Created: 28/Dec/18 08:15
• Updated: 11/Jan/23 07:31
• Resolved: 31/Dec/18 23:47

Description

• It seems we are using doxygen style comments for method/class declaration ("///")
• Use the macro NULLPTR (https://arrow.apache.org/docs/cpp/macros_8h.html 

Issue Links

• links to: GitHub Pull Request #3284