char *test ();Then, there is a main program called program.c that uses the header file, like the following.
int x; #include "header.h" main () { printf (test ()); }The output generated by the C preprocessor for program.c as input would be as follows.
int x; char *test (); main () { printf (test ()); }Included files are not limited to declarations and macro definitions; those are merely the typical uses. Any fragment of a C program can be included from another file. The include file could even contain the beginning of a statement that is concluded in the containing file, or the end of a statement that was started in the including file. However, a comment or a string or character constant may not start in the included file and finish in the including file. An unterminated comment, string constant or character constant in an included file is considered to end (with an error message) at the end of the file.
It is possible for a header file to begin or end a syntactic unit such as a function definition, but that would be very confusing, so don’t do it.
The
line following the #include
directive is always treated as a separate line by the C preprocessor even
if the included file lacks a final newline.