C++ Anonymous Struct

This tutorial demonstrates the use of anonymous structs in C++.

Anonymous Struct in C++

Anonymous structs are not supported in C++ as it was also not supported in C language, but C++ does support anonymous unions, unlike C. According to ANSI C and C++ standards on structs and unions:

1. ANSI C++ anonymous unions: Supported
2. ANSI C++ anonymous structs: Not Supported
3. ANSI C anonymous unions: Supported
4. ANSI C anonymous structs: Not Supported

C++ doesn’t support anonymous structs because C doesn’t support it, which is necessary for compatibility. There is no use of anonymous structs in C++, but it provides some alternatives.

For example, see the code below.

struct DemoVector {
  float v[3];
  float &operator[](int x) { return v[x]; }

  float &a() { return v[0]; }
  float &b() { return v[1]; }
  float &c() { return v[2]; }
};

The code above provides facilities for user-defined types similar to anonymous structs. A similar thing can be done using the unions in C++.

See the code below.

union DemoVector {
  struct {
    float a, b, c;
  };
  float v[3];
};

The anonymous structs are now permitted in ISO C11, gcc, and Apple’s llvm but not supported with ISO C++11.