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Compiler Error C2065

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The latest version of this topic can be found at Compiler Error C2065.

identifier' : undeclared identifier

A variable's type must be specified in a declaration before it can be used. The parameters that a function uses must be specified in a declaration, or prototype, before the function can be used.

Possible causes:

  1. Identifier name is misspelled.

  2. Identifier uses the wrong uppercase and lowercase letters.

  3. Missing closing quote after a string constant.

  4. You are compiling with a debug version of the C runtime, declaring a Standard C++ Library iterator variable in a for loop, and then trying to use that iterator variable outside the scope of the for loop. Compiling C++ Standard Library code with a debug version of the C runtime implies /Zc:forScope. See Debug Iterator Support for more information.

  5. You may be calling a function in an SDK header file that is currently not supported in your build environment.

  6. Omitting necessary include files, especially if you define VC_EXTRALEAN, WIN32_LEAN_AND_MEAN, or WIN32_EXTRA_LEAN. These symbols exclude some header files from windows.h and afxv_w32.h to speed compiles. (Look in windows.h and afxv_w32.h for an up-to-date description of what's excluded.)

  7. Improper namespace scope. For example, to resolve C++ Standard Library functions and operators that are not fully qualified, you must specify the std namespace with the using directive. The following example fails to compile because the using directive is commented out and cout is defined in the std namespace:

Example

The following sample generates C2065 and shows how to fix it.

// C2065.cpp  
// compile with: /EHsc  
// using namespace std;   // Uncomment this line to fix  
#include <iostream>  
int main() {  
   cout << "Hello" << endl;   // C2065  
  
   // Or try the following line instead  
   std::cout << "Hello" << std::endl;  
}

Example

When calling a generic function, if the intended type argument cannot be deduced from the parameters used, the compiler will report an error. For more information, see Generic Functions (C++/CLI).

The following sample generates C2065 and shows how to fix it.

// C2065_b.cpp  
// compile with: /clr  
generic <typename ItemType>  
void G(int i) {}  
  
int main() {  
   // global generic function call  
   G<T>(10);   // C2065  
   G<int>(10);   // OK - fix with a specific type argument  
}

Example

This error can also be generated as a result of compiler conformance work that was done for Visual C++ 2005: parameter checking for Visual C++ attributes.

The following sample generates C2065 and shows how to fix it.

// C2065_c.cpp  
// compile with: /c  
[module(DLL, name=MyLibrary)];   // C2065  
// try the following line instead  
// [module(dll, name="MyLibrary")];  
  
[export]  
struct MyStruct {  
   int i;  
};