V570. The variable is assigned to itself

29.04.2011

The analyzer detected a potential error: a variable is assigned to itself. Consider this sample:

dst.m_a = src.m_a;
dst.m_b = dst.m_b;

The value of the 'dst.m_b' variable will not change because of the misprint. This is the correct code:

dst.m_a = src.m_a;
dst.m_b = src.m_b;

The analyzer does not produce the warning every time it detects assignment of a variable to itself. For example, if the variables are enclosed in parentheses. This method is often used to suppress compiler-generated warnings. For example:

int Foo(int foo)
{
  UNREFERENCED_PARAMETER(foo);
  return 1;
}

The UNREFERENCED_PARAMETER macro is defined in the WinNT.h file in the following way:

#define UNREFERENCED_PARAMETER(P)          \
  { \
      (P) = (P); \
  } 

The analyzer knows about such cases and will not generate the V570 warning on assignment like this:

(foo) = (foo);

Note. If V570 warning shows on macro that should not be changed, it is possible to use macro suppression mechanism. Special comment in the file that is used in the whole project (for instance, StdAfx.h file) may be enough for that. Example:

//-V:MY_MACROS:V570
You can look at examples of errors from real projects which were detected by this diagnostic message.