15 Preprocessing directives [cpp]

15.4 Resource inclusion [cpp.embed]

15.4.2 Embed parameters [cpp.embed.param]

15.4.2.5 if_empty parameter [cpp.embed.param.if.empty]

1
#
An embed-parameter of the form
if_empty ( pp-balanced-token-seq )
shall appear at most once in the embed-parameter-seq.
2
#
If the resource is not empty, this embed-parameter is ignored.
Otherwise, the #embed directive is replaced by the pp-balanced-token-seq.
[Example 1: 
limit(0) affects when a resource is considered empty.
Therefore, the following program:
#embed </owo/uwurandom> \ if_empty(42203) limit(0) expands to 42203
— end example]
[Example 2: 
This resource is considered empty due to the limit(0) embed-parameter, always, including in __has_embed clauses.
int infinity_zero () { #if __has_embed(</owo/uwurandom> limit(0) prefix(some tokens)) == __STDC_EMBED_EMPTY__ // if </owo/uwurandom> exists, this conditional inclusion branch is taken and the function returns 0. return 0; #else // otherwise, the resource does not exist #error "The resource does not exist" #endif } — end example]
[Example 3: 
Given a resource <single_byte> that has an implementation-resource-count of 1, the following directives: #embed <single_byte> offset(1) if_empty(42203) are replaced with: 42203
— end example]