Why replace an existing keyword in C/C with a macro?-CodePudding

I often come across keywords or one-word identifiers defined with another name. For example, boost defines noexcept as BOOST_NOEXCEPT, some C standard libraries replace [[nodiscard]] with _NODISCARD, Windows API is prone to introduce their own macros as well, and so forth. I didn't really manage to find anything which would explain this.

This makes an unfamiliar person search for what such macros mean which therefore makes the code a bit harder to understand (at least this is how I see it). Why is such tendency so widespread? What is the purpose of replacing existing one-word constructs with macros?

CodePudding user response：

The most useful case of these is when you target both compilers that support a new feature and ones that do not.
For instance:

#if CompilerSupportsNoexcept
#define NOEXCEPT noexcept
#else
#define NOEXCEPT
#endif

CodePudding user response：

This may be used in different scenarios for flexibility and code clarity. Following cases come in mind:

support for different compilers, which implements the same feature in a different way or do not support at all
support for different build options, i.e. building static vs dynamic library
support for different OSes (functions, exported by dynamic libraries, in Windows and Linux would have different signatures.
Debug vs Release builds