Book index · ← Library

← Prev · 99/277 · Next →

"

or

filename

is replaced by the contents of the file

filename

. If the

filename

is quoted, searching for the file typically begins where the source program

was found; if it is not found there, or if the name is enclosed in < and

included file may itself contain

lines.

There are often several #include lines at the beginning of a source file, to include common #define statements and extern declarations, or to access the function prototype declarations for library functions from headers like <stdio.h>. (Strictly speaking, these need not be files; the details of how headers are accessed are implementation-dependent.)

A definition has the form

name replacement text

It calls for a macro substitution of the simplest kind - subsequent

occurrences of the token

name

will be replaced by the

replacement text

. The name in a

has the same form

as a variable name; the replacement text is arbitrary. Normally the

replacement text is the rest of the line, but a long definition may be

continued onto several lines by placing a

at the end of each line

to be continued. The scope of a name defined with

is from

its point of definition to the end of the source file being compiled. A

definition may use previous definitions. Substitutions are made only for

tokens, and do not take place within quoted strings. For example, if

YES

is a defined name, there would be no substitution in

printf("YES")

or in

YESMAN

.

Any name may be defined with any replacement text. For example

defines a new word,

forever

, for an infinite loop.