#ifndef

Starts a conditional assembly block, making assembly conditional on a symbol not being defined.

  #ifndef symbol statement-group

Parameter

symbol

Any valid symbol.

statement-group

Any valid assembly statements.

Remarks

If previous code does not include a definition for symbol, the preprocessor implements the statements of the block. If there is a definition for symbol, the preprocessor skips the statements of the block.

Each #ifndef directive must have a matching #endif directive.