#if

Starts a conditional assembly block, making assembly conditional on the truth of a boolean expression.

  #if bool-expr statement-group

Parameters

bool-expr

Any boolean expression.

statement-group

Any valid assembly statements.

Remarks

This directive starts an #if ... [#elif] ... [#else] ... #endif conditional structure (with each of these directives starting a new line). There must be a corresponding #endif directive for each #if directive. An #else directive is optional; one or more #elif directives are optional.

The simplest such conditional structure follows the pattern #if ... assembly statements ... #endif. The preprocessor implements the assembly statements only if the #if directive's bool-expr condition is true.

The next simplest conditional structure follows the pattern #if ... assembly statements 1 ... #else ... assembly statements 2 ... #endif. The preprocessor implements the assembly statements 1 if the #if directive's bool-expr condition is true; the preprocessor implements assembly statements 2 if the condition is false.

You can use #elif directives to create increasingly complex conditional structures.