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.