Compiler Warning (level 4) C4201

nonstandard extension used : nameless struct/union

Microsoft C/C++ allows structure declarations to be specified without a declarator when they are members of another structure or union.

The following is an example of this error:

struct S
{
   float y;
   struct
   {
      int a, b, c;  // warning
   };
} *p_s;

This extension can prevent your code from being portable to other compilers and will generate an error under the /Za command-line option.