Two-level macros & string macros

If you want to serialize the macro parameter extension results, you must use two levels of macros.

1 # define xstr (s) STR (S) 2 # define STR (s) # S3 # define Foo 44 STR (FOO) 5 => "foo" 6 xstr (FOO) 7 ==> xstr (4) 8 ==> STR (4) 9 ==> "4"

When S is used in STR, S is stringized, so it is not a macro extension first.

However, S is a common parameter of xstr. Therefore, s itself has been expanded before the xstr macro extension is complete.

When STR reaches its parameter, it is already a macro extension. When xstr processes its own parameter Foo, foo is expanded.

Solution Source

Https://gcc.gnu.org/

Two-level macros & string macros