хедеры

1 A #include directive shall identify a header or source file that can be processed by the implementation.

2 A preprocessing directive of the form

# include < h-char-sequence> new-line

searches a sequence of implementation-defined places for a header identified uniquely by the specified se-
quence between the < and > delimiters, and causes the replacement of that directive by the entire contents
of the header. How the places are specified or the header identified is implementation-defined.

3 A preprocessing directive of the form

# include " q-char-sequence" new-line

causes the replacement of that directive by the entire contents of the source file identified by the specified
sequence between the " delimiters. The named source file is searched for in an implementation-defined
manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read

# include < h-char-sequence> new-line

with the identical contained sequence (including > characters, if any) from the original directive.

4 A preprocessing directive of the form

# include pp-tokens new-line

(that does not match one of the two previous forms) is permitted. The preprocessing tokens after include
in the directive are processed just as in normal text (Each identifier currently defined as a macro name is
replaced by its replacement list of preprocessing tokens.). If the directive resulting after all replacements
does not match one of the two previous forms, the behavior is undefined.150 The method by which a sequence

of preprocessing tokens between a < and a > preprocessing token pair or a pair of " characters is combined
into a single header name preprocessing token is implementation-defined.