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V570. Variable is assigned to itself.
Analyzer diagnostics
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V570. Variable is assigned to itself.

08 Aoû 2019

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 issues a warning not only for the copy assignment, but for the move assignment too.

dst.m_a = std::move(src.m_a);

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);

If such an approach isn't used in your project, you can add the following comment to enable the warning:

//V_WARN_ON_ARGUMENT_SELF_ASSIGN

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

This diagnostic is classified as:

You can look at examples of errors detected by the V570 diagnostic.

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