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__if_not_exists Statement

The __if_not_exists statement tests whether the specified identifier exists. If the identifier does not exist, the specified statement block is executed.

__if_not_exists ( identifier ) { 
statements
};

Parameter

Description

identifier

The identifier whose existence you want to test.

statements

One or more statements to execute if identifier does not exist.

Caution note Caution

To achieve the most reliable results, use the __if_not_exists statement under the following constraints.

  • Apply the __if_not_exists statement to only simple types, not templates.

  • Apply the __if_not_exists statement to identifiers both inside or outside a class. Do not apply the __if_not_exists statement to local variables.

  • Use the __if_not_exists statement only in the body of a function. Outside of the body of a function, the __if_not_exists statement can test only fully defined types.

  • When you test for overloaded functions, you cannot test for a specific form of the overload.

The complement to the __if_not_exists statement is the __if_exists statement.

For an example about how to use __if_not_exists, see __if_exists Statement.

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