### #undef Preprocessor Directive

A preprocessor undef directive causes the preprocessor to end the scope of a preprocessor definition.

If the identifier is not currently defined as a macro, #undef is ignored

Example of Usage
The following directives define `BUFFER` and `SQR`:

    #define BUFFER 512
    #define SQR(x) ((x) * (x))

`The following directives nullify these definitions:`

    #undef BUFFER
    #undef SQR

Any occurrences of the identifiers `BUFFER` and `SQR` that follow these #undef directives are not replaced with any replacement tokens. Once the definition of a macro has been removed by an #undef directive, the identifier can be used in a new #define directive.

Preprocessor Macros
Preprocessor Directives

#define Preprocessor Directive
List of Preprocessor Directives