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Oracle Solaris Studio 12.3: C++ User's Guide     Oracle Solaris Studio 12.3 Information Library
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Part I C++ Compiler

1.  The C++ Compiler

2.  Using the C++ Compiler

3.  Using the C++ Compiler Options

Part II Writing C++ Programs

4.  Language Extensions

4.1 Linker Scoping

4.1.1 Compatibility with Microsoft Windows

4.2 Thread-Local Storage

4.3 Overriding With Less Restrictive Virtual Functions

4.4 Making Forward Declarations of enum Types and Variables

4.5 Using Incomplete enum Types

4.6 Using an enum Name as a Scope Qualifier

4.7 Using Anonymous struct Declarations

4.8 Passing the Address of an Anonymous Class Instance

4.9 Declaring a Static Namespace-Scope Function as a Class Friend

4.10 Using the Predefined __func__ Symbol for Function Name

4.11 Supported Attributes

4.11.1 __packed__ Attribute Details

4.12 Compiler Support for Intel MMX and Extended x86 Platform Intrinsics

5.  Program Organization

6.  Creating and Using Templates

7.  Compiling Templates

8.  Exception Handling

9.  Improving Program Performance

10.  Building Multithreaded Programs

Part III Libraries

11.  Using Libraries

12.  Using the C++ Standard Library

13.  Using the Classic iostream Library

14.  Building Libraries

Part IV Appendixes

A.  C++ Compiler Options

B.  Pragmas



4.7 Using Anonymous struct Declarations

An anonymous struct declaration is a declaration that declares neither a tag for the struct, nor an object or typedef name. Anonymous structs are not allowed in C++.

The -features=extensions option allows the use of an anonymous struct declaration but only as member of a union.

The following code is an example of an invalid anonymous struct declaration that compiles when you use the -features=extensions option.

union U {
  struct {
    int a;
    double b;
  };  // invalid: anonymous struct
  struct {
    char* c;
    unsigned d;
  };  // invalid: anonymous struct

The names of the struct members are visible without qualification by a struct member name. Given the definition of U in this code example, you can write:

U u;
u.a = 1;

Anonymous structs are subject to the same limitations as anonymous unions.

Note that you can make the code valid by giving a name to each struct, for example:

union U {
  struct {
    int a;
    double b;
  } A;
  struct {
    char* c;
    unsigned d;
  } B;
U u;
U.A.a = 1;