Object-like macros

An object-like macro definition replaces a single identifier with the specified replacement tokens. The following object-like definition causes the preprocessor to replace all subsequent instances of the identifier COUNT with the constant 1000 :

#define COUNT 1000

If the statement

int arry[COUNT];

appears after this definition and in the same file as the definition, the preprocessor would change the statement to

int arry[1000];

in the output of the preprocessor.

Other definitions can make reference to the identifier COUNT:

#define MAX_COUNT COUNT + 100

The preprocessor replaces each subsequent occurrence of MAX_COUNT with COUNT + 100, which the preprocessor then replaces with 1000 + 100.

If a number that is partially built by a macro expansion is produced, the preprocessor does not consider the result to be a single value. For example, the following will not result in the value 10.2 but in a syntax error.

#define a 10
a.2

Identifiers that are partially built from a macro expansion may not be produced. Therefore, the following example contains two identifiers and results in a syntax error:

#define d efg
abcd