2.1 Include Syntax
Both user and system header files are included using the preprocessing directive ` #include '. It has two variants:
-
#include <
file>
- This variant is used for system header files. It searches for a file named file in a standard list of system directories. You can prepend directories to this list with the
-I
option (see Invocation).
-
#include "
file"
- This variant is used for header files of your own program. It searches for a file named file first in the directory containing the current file, then in the quote directories and then the same directories used for
<
file>
. You can prepend directories to the list of quote directories with the -iquote option.
The argument of `
#include
', whether delimited with quote marks or angle brackets, behaves like a string constant in that comments are not recognized, and macro names are not expanded. Thus, #include <x/*y>
specifies inclusion of a system header file named
x/*y
.
However, if backslashes occur within file, they are considered ordinary text characters, not escape characters. None of the character escape sequences appropriate to string constants in C are processed. Thus, #include "x\n\\y"
specifies a filename containing three backslashes. (Some systems interpret `
\
' as a pathname separator. All of these also interpret `
/
' the same way. It is most portable to use only `
/
'.)
It is an error if there is anything (other than comments) on the line after the file name.