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title: "__if_exists Statement | Microsoft Docs"
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---
# __if_exists Statement
The `__if_exists` statement tests whether the specified identifier exists. If the identifier exists, the specified statement block is executed.  
  
## Syntax  
  
```  
__if_exists ( identifier ) {   
statements  
};  
```  
  
#### Parameters  
  
|Parameter|Description|  
|---------------|-----------------|  
|`identifier`|The identifier whose existence you want to test.|  
|`statements`|One or more statements to execute if `identifier` exists.|  
  
## Remarks  
  
> [!CAUTION]
>  To achieve the most reliable results, use the `__if_exists` statement under the following constraints.  
  
-   Apply the `__if_exists` statement to only simple types, not templates.  
  
-   Apply the `__if_exists` statement to identifiers both inside or outside a class. Do not apply the `__if_exists` statement to local variables.  
  
-   Use the `__if_exists` statement only in the body of a function. Outside of the body of a function, the `__if_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_exists` statement is the [__if_not_exists](../cpp/if-not-exists-statement.md) statement.  
  
## Example  
 Notice that this example uses templates, which is not advised.  
  
```  
// the__if_exists_statement.cpp  
// compile with: /EHsc  
#include <iostream>  
  
template<typename T>  
class X : public T {  
public:  
   void Dump() {  
      std::cout << "In X<T>::Dump()" << std::endl;  
  
      __if_exists(T::Dump) {  
         T::Dump();  
      }  
  
      __if_not_exists(T::Dump) {  
         std::cout << "T::Dump does not exist" << std::endl;  
      }  
   }     
};  
  
class A {  
public:  
   void Dump() {  
      std::cout << "In A::Dump()" << std::endl;  
   }  
};  
  
class B {};  
  
bool g_bFlag = true;  
  
class C {  
public:  
   void f(int);  
   void f(double);  
};  
  
int main() {   
   X<A> x1;  
   X<B> x2;  
  
   x1.Dump();  
   x2.Dump();  
  
   __if_exists(::g_bFlag) {  
      std::cout << "g_bFlag = " << g_bFlag << std::endl;  
   }  
  
   __if_exists(C::f) {  
      std::cout << "C::f exists" << std::endl;  
   }  
  
   return 0;  
}  
```  
  
## Output  
  
```  
In X<T>::Dump()  
In A::Dump()  
In X<T>::Dump()  
T::Dump does not exist  
g_bFlag = 1  
C::f exists  
```  
  
## See Also  
 [Selection Statements](../cpp/selection-statements-cpp.md)   
 [Keywords](../cpp/keywords-cpp.md)   
 [__if_not_exists Statement](../cpp/if-not-exists-statement.md)