Compiler Error C3861

Artikkel
06/30/2022

'identifier': identifier not found

The compiler was unable to resolve a reference to an identifier, even using argument-dependent lookup.

Remarks

To fix this error, compare use of identifier to the identifier declaration for case and spelling. Verify that scope resolution operators and namespace using directives are used correctly. If the identifier is declared in a header file, verify that the header is included before the identifier is referenced. If the identifier is meant to be externally visible, make sure that it's declared in any source file that uses it. Also check that the identifier declaration or definition isn't excluded by conditional compilation directives.

Changes to remove obsolete functions from the C Runtime Library in Visual Studio 2015 can cause C3861. To resolve this error, remove references to these functions or replace them with their secure alternatives, if any. For more information, see Obsolete functions.

If error C3861 appears after project migration from older versions of the compiler, you may have issues related to supported Windows versions. Visual C++ no longer supports targeting Windows 95, Windows 98, Windows ME, Windows NT or Windows 2000. If your WINVER or _WIN32_WINNT macros are assigned to one of these versions of Windows, you must modify the macros. For more information, see Modifying WINVER and _WIN32_WINNT.

Examples

Undefined identifier

The following sample generates C3861 because the identifier isn't defined.

// C3861.cpp
void f2(){}
int main() {
   f();    // C3861
   f2();   // OK
}

Identifier not in scope

The following sample generates C3861, because an identifier is only visible in the file scope of its definition, unless it's declared in other source files that use it.

Source file C3861_a1.cpp:

// C3861_a1.cpp
// Compile with: cl /EHsc /W4 C3861_a1.cpp C3861_a2.cpp
#include <iostream>
// Uncomment the following line to fix:
// int f();  // declaration makes external function visible
int main() {
   std::cout << f() << std::endl;    // C3861
}

Source file C3861_a2.cpp:

// C3861_a2.cpp
int f() {  // declared and defined here
   return 42;
}

Namespace qualification required

Exception classes in the C++ Standard Library require the std namespace.

// C3861_b.cpp
// compile with: /EHsc
#include <iostream>
int main() {
   try {
      throw exception("Exception");   // C3861
      // try the following line instead
      // throw std::exception("Exception");
   }
   catch (...) {
      std::cout << "caught an exception" << std::endl;
   }
}

Obsolete function called

Obsolete functions have been removed from the CRT library.

// C3861_c.cpp
#include <stdio.h>
int main() {
   char line[21]; // room for 20 chars + '\0'
   gets( line );  // C3861
   // Use gets_s instead.
   printf( "The line entered was: %s\n", line );
}

ADL and friend functions

The following sample generates C3767 because the compiler can't use argument dependent lookup for FriendFunc:

namespace N {
   class C {
      friend void FriendFunc() {}
      friend void AnotherFriendFunc(C* c) {}
   };
}

int main() {
   using namespace N;
   FriendFunc();   // C3861 error
   C* pC = new C();
   AnotherFriendFunc(pC);   // found via argument-dependent lookup
}

To fix the error, declare the friend in class scope and define it in namespace scope:

class MyClass {
   int m_private;
   friend void func();
};

void func() {
   MyClass s;
   s.m_private = 0;
}

int main() {
   func();
}

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