| title | __if_not_exists Statement | Microsoft Docs | |||||||||||||
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| ms.date | 11/04/2016 | |||||||||||||
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| ms.topic | language-reference | |||||||||||||
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| ms.assetid | a2f322d4-e96f-4a32-954e-4323d20c6e32 | |||||||||||||
| caps.latest.revision | 9 | |||||||||||||
| author | mikeblome | |||||||||||||
| ms.author | mblome | |||||||||||||
| manager | ghogen | |||||||||||||
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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
To achieve the most reliable results, use the __if_not_exists statement under the following constraints.
-
Apply the
__if_not_existsstatement to only simple types, not templates. -
Apply the
__if_not_existsstatement to identifiers both inside or outside a class. Do not apply the__if_not_existsstatement to local variables. -
Use the
__if_not_existsstatement only in the body of a function. Outside of the body of a function, the__if_not_existsstatement 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.