15 Preprocessing directives [cpp]

15.4 Resource inclusion [cpp.embed]

15.4.2 Embed parameters [cpp.embed.param]

15.4.2.2 prefix parameter [cpp.embed.param.prefix]

1
#
An embed-parameter of the form
prefix ( pp-balanced-token-seq )
shall appear at most once in the embed-parameter-seq.
2
#
If the resource is empty, this embed-parameter is ignored.
Otherwise, the pp-balanced-token-seq is placed immediately before the comma-delimited list of integral literals.