Compiler Warning (level 2) C4826

The latest version of this topic can be found at Visual Studio 2017 Documentation. Conversion from 'type1 ' to 'type_2' is sign-extended. This may cause unexpected runtime behavior.

This warning indicates that the compiler performed sign extension when a 32-bit pointer was cast to a 64-bit variable.

If the extension was performed on a windows HANDLE type, it is safe to ignore this warning. If the extension was performed on a pointer type, you should modify the cast to prevent the sign extension (see example below).

C4826 is off by default. See Compiler Warnings That Are Off by Default for more information.

Example

The following sample generates C4826.

// C4826.cpp  
// compile with: /W2 /c  
#include <windows.h>  
#pragma warning(default: 4826)  
  
void * __ptr64 F1 (void * __ptr32 P ) {  
   return (void * __ptr64)P;   // C4826  
   // try the following line instead  
   // return (void * __ptr64)(ULONGLONG)(ULONG)P;  
}  
  
void * __ptr64 F2 ( void * P ) {  
   return (void * __ptr64)P;   // C4826  
   // try the following line instead  
   // return (void * __ptr64)(ULONGLONG)(ULONG)P;  
}  
  
unsigned __int64 F3r ( void * P ) {  
   return (unsigned __int64)P;   // C4826  
   // try the following line instead  
   // return (unsigned __int64)(ULONGLONG)(ULONG)P;  
}